A comprehensive review on the rheological behavior

Journal of Molecular Liquids 277 (2019) 932–958

Contents lists available at ScienceDirect

Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

Review

A comprehensive review on the rheological behavior of imidazolium based ionic liquids and natural deep eutectic solvents Yousef A. Elhamarnah a, Mustafa Nasser a,⁎, Hazim Qiblawey b, Abdelbaki Benamor a, Mert Atilhan c,d,⁎⁎, Santigo Aparicio e a

Gas Processing Center, College of Engineering, Qatar University, Doha, Qatar Department of Chemical Engineering, College of Engineering, Qatar University, Doha, Qatar Department of Chemical Engineering, Texas A&M University at Qatar, Doha, Qatar d Gas and Fuels Research Center, Texas A&M University, College Station, TX, USA e Department of Chemistry, University of Burgos, Burgos, Spain b c

a r t i c l e

i n f o

Article history: Received 12 September 2018 Received in revised form 6 December 2018 Accepted 1 January 2019 Available online 06 January 2019 Keywords: Ionic liquids Imidazolium Deep eutectic solvents Rheology Viscoelastic Choline chloride, viscosity

a b s t r a c t The rheological behavior of a fluid is an important property that has a distinct impact on its flow conduct, which influence viscosity dependent phenomena and applications such as pumping, mass transfer rates, and hydrodynamics. As a result, the necessity of studying the different rheograms and the viscoelastic properties of fluids is essential. In this review, a vast number of novel imidazolium-based combinations of ionic liquids (IL) and natural deep eutectic solvents (NADES) in terms of different hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA) having different molar ratios of HBA:HBD were classified. The rheological behaviors of these combinations at ambient temperature conditions and higher temperatures are critically evaluated. The influence of different parameters such as the effect of adding different polymers, metal oxides, and water on the rheological behaviors and eventually on the flow assurance of these solvents are investigated. Moreover, an intensive overview of all the key research papers, mainly highlighting the initial apparent viscosity and steady-state viscosity for both IL & NADES solvents with different scenarios was conducted by collecting the different trends in rheograms using different measuring devices from several experimental efforts. Also, the relatively few studies on the oscillatory measurement was also highlighted, as it has shown to be a useful analysis method to determine the elastic properties. In addition, oscillatory mode measurements were best to describe and enhance studies on IL and NADES with high viscosities, which can aid their potential uses in challenging applications such as in pumping of liquid material in many industrial processes, through the study of their elasticity behaviors under the effect of several field operation conditions. Furthermore, eight different rheological regression models from different polynomial degrees were used to describe and physically interpret the viscous and viscoelastic behaviors of the studied solvents. © 2019 Elsevier B.V. All rights reserved.

Contents 1. 2.

Introduction . . . . . . . . . . . . . . Shear flow behaviors . . . . . . . . . . 2.1. Ambient Temperature. . . . . . . 2.1.1. NADES . . . . . . . . . 2.1.2. ILs . . . . . . . . . . . 2.2. Temperature dependency of NADES 2.3. Hydration effect on NADES . . . . 2.4. Hydration effect on ILs . . . . . .

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⁎ Corresponding author. ⁎⁎ Correspondence to: M. Atilhan, Department of Chemical Engineering, Texas A&M University at Qatar, Doha, Qatar. E-mail addresses: [email protected] (M. Nasser), [email protected] (M. Atilhan).

https://doi.org/10.1016/j.molliq.2019.01.002 0167-7322/© 2019 Elsevier B.V. All rights reserved.

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933 944 944 944 945 946 948 948

Y.A. Elhamarnah et al. / Journal of Molecular Liquids 277 (2019) 932–958

3.

Viscoelasticity . . . . . . . . . . . . . . . 3.1. Viscoelastic behavior of ILs . . . . . . 3.2. Viscoelastic behavior of NADES . . . . 4. Rheological models . . . . . . . . . . . . . 4.1. Arrhenius equation. . . . . . . . . . 4.2. Vogel-Fulcher-Tammann equation . . . 4.3. Ostwald-de Waele power-law equation 4.4. Power law equation . . . . . . . . . 4.5. Litovitz equation . . . . . . . . . . . 4.6. Ghatee equation . . . . . . . . . . . 4.7. Herschel-Bulkley equation . . . . . . 4.8. Bingham equation . . . . . . . . . . 5. Conclusion . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . .

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933

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949 949 952 953 953 954 954 954 954 955 955 955 956 957

A pivotal factor for the development of sustainable chemical processes stands on the availability of novel chemical agents and solvents [1,2]. Among those solvents the ones that allow fine-tuning of thermophysical properties for targeted operations and processes via alternations and/or variations of chemical constituents or physical parameters have gained considerable attention in recent years [3–5]. Ionic liquids (ILs) and deep eutectic solvents (DESs) are considered as emerging novel solvents that allow such variations and they have attracted the attention from both academia and industry during the last decade [6,7]. The large number of possible constituents stands as main advantage of these solvents as they allow task specific design of fluids for various technological applications [8–12]. Rheology is one of the crucial branches of science that deals with the flow of matter and deformation behaviors of fluids. The rheological measurements on IL and DES have established a wide interest in becoming a major tool in laboratories for the characterization of the recently developed materials and products for industrial and field applications. Rheological studies aid the characterization of material by understanding their structure and flow properties, to ensure their success prior their application on large scale processes. Rheology also enhances the opportunities of studying fluid microscopic structure of a certain system, by measuring the macroscopic flow regime under varied magnitudes of shear, which can be considered as an ideal methodology for studies both on ILs and DES. The application of rheology varies from one class of solvents to another, due to their unique structural properties and different responses under mechanical behavior during processing. Both of these behaviors correspond to the composition and nature

of the material, which govern the application of the solvent. The objectives of applying rheological studies on IL and DES fall into several improved categories; in order to understand the solvation properties in action, gaining an insight on the main rheological triggers such as the flow properties (i.e. apparent viscosity) and elasticity/rigidity (viscoelasticity) of DES and ILs under different operational conditions that may hinder processing such as ambient or high operating temperatures, co-solvent blending's (additives) and levels of hydration content. Moreover, the oscillatory studies have significant effect on the IL/DES in order to understand how they will perform under stress and pressurized applications. The available literature that has been generated in the last decade on both DES and natural deep eutectic solvents (NADES) thermophysical properties include mostly density, viscosity and gas solubilities (e.g. CO2, N2). [13–18]. Some recent works proposed these materials as novel gas capture agents, which can replace conventional currentstate-of-the-art amine-based solvents that are used for the same purpose, with the target of zero (or minimum) retrofitting cost on the process infrastructure. One of the major challenges of these materials is to regulate their pumping costs and deal with their viscous behavior. In order to for regulatory authorities to consider DES or NADES as alternatives solvents for the above-explained purposes in larger scales, thermophysical properties that include gas solubility performance as well as detailed rheological behavior must be investigated for various potential systems and a systematic analysis of these materials shall be handled in wide scale. Therefore, we believe that this review work is crucially important for benchmarking the key rheological properties of NADES and this work includes a thorough review analysis of currently available published information on this matter.

Fig. 1. Rheological characterization of different material under the effect of shear rate.

Fig. 2. Apparent viscosity of a fluid that depends on the shear rate at which it is measured.

1. Introduction

934

Table 1 Overview on the rheological characterization and experimental setups for shear flow behaviors for varies tailor-made Imidazolium based ILs. Full name

1‑butyl‑3‑methylimadolium chloride 1‑butyl‑3‑methylimadolium chloride 1‑butyl‑3‑methylimadolium chloride 1‑butyl‑3‑methylimadolium chloride

1‑ethyl‑3‑methylimadolium tosylote



1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote




1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑butyl‑3‑methylimadolium bis(trifluoromethyl Sulfonyl)imide

0.2 wt% cellulose +0.0 wt% water 0.2 wt% cellulose +1.0 wt% water 0.2 wt% cellulose +2.0 wt% water 0.2 wt% cellulose +3.0 wt% water – – – – diluted non-aligned mwcntS diluted non-aligned mwcntS diluted non-aligned mwcntS diluted non-aligned mwcntS diluted aligned MWCNT diluted aligned MWCNT diluted aligned MWCNT diluted aligned MWCNT Concentrated non-aligned mwcntS Concentrated non-aligned mwcntS Concentrated non-aligned mwcntS Concentrated non-aligned mwcntS Concentrated aligned MWCNT Concentrated aligned MWCNT Concentrated aligned MWCNT Concentrated aligned MWCNT

Rheometer specifications Model

Plate configuration

Discovery Hybrid Rheometer (DHR-3) from TA Instruments

20,60 mm cone and plate geometries

AR-G2 rotational rheometer + Peltier system

Simulation and modeling

60 mm parralel plate

–

Gap

26,28 μm

–

–

Viscosity Vs shear rate

Viscosity vs temperature

Shear rate range

Temperature Initial Steady-state viscosity viscosity

Temperature Initial STEADY-STATE viscosity VISCOSITY

Fixed shear rate

s−1

o

o

s−1

C

(Pa·s)

(Pa·s)

C

(Pa·s)

References

(Pa·s)

0.01–100

20

1.9

1.8

–

–

–

–

0.01–100

20

14

1.5

–

–

–

–

0.01–100

20

17

1.2

–

–

–

–

0.01–100

20

22

0.48

–

–

–

–

0.0001–1000 0.0001–1000 0.0001–1000 0.0001–1000 0.0001–1000

25 50 75 100 25

6 3 0.09 0.07 3.5

0.75 0.093 0.055 0.012 0.178

20–100 – – – 20–100

0.00048 – – – 0.00027

0.00002 – – – 0.000001

50 – – – 50

0.0001–1000

50

1

0.08

–

–

–

–

0.0001–1000

75

0.1

0.024

–

–

–

–

0.0001–1000

100

0.2

0.012

–

–

–

–

0.0001–1000

25

2

0.302

20–100

0.00035

0.000005

50

0.0001–1000

50

2

0.084

0.0001–1000

75

0.9

0.03

0.0001–1000

100

0.1

0.016

0.0001–1000

25

1

0.8

0.0001–1000

50

0.25

0.2

0.0001–1000

75

0.95

0.06

0.0001–1000

100

0.9

0.03

0.0001–1000

25

30

0.45

0.0001–1000

50

20

0.09

0.0001–1000

75

70

0.06

0.0001–1000

100

100

0.03

0.00001–1

25

0.07

0.0003

[65]

[53]


1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote

Additives

[52]

1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium chloride 1‑doecyl‑3‑methylimidazolium bromide 1‑doecyl‑3‑methylimidazolium bromide 1‑ethyl‑3‑methylimidazolium hexafluoroposphate 1‑ethyl‑3‑methylimidazolium hexafluoroposphate 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate

– – – – – – – – – – – – – – – – – –

TA Instruments AR-G2 + Peltier plate and jacket with

1000 μm

10–5000 10–5000 10–5000 10–5000 10–5000 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 10–60 0.1–100 0.1–100

23 23 23 23 23 10 15 20 25 30 35 40 45 50 55 60 65 10 15 20 25 30 35 40 45 50 55 25 25

0.144 0.071 0.035 0.029 0.01 0.68 0.49 0.34 0.26 0.2 0.15 0.12 0.09 0.08 0.07 0.05 0.045 0.44 0.29 0.21 0.15 0.13 0.09 0.075 0.05 0.04 0.03 0.11 0.2

0.142 0.06 0.03 0.025 0.011 0.67 0.48 0.33 0.25 0.19 0.16 0.13 0.1 0.09 0.07 0.05 0.05 0.45 0.3 0.22 0.16 0.14 0.1 0.077 0.05 0.05 0.03 0.15 0.2

0.1–100

25

0.3

0.35

0.1–100

25

0.5

0.5

0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000

25 25 25 25 25 90 90 90 90 120 120 120 120 90 90 25

1.6 6.8 30 70 300 180 85 200 100 0.2 0.18 0.08 0.12 0.19 0.055 0.07

1 3.5 6 15 40 0.9 0.8 0.9 0.7 0.09 0.09 0.06 0.06 0.016 0.016 0.08

0.1–1000

25

0.11

0.08

50

0.5 wt% SiO2

0.1–1000

25

0.1

0.09

50

1 wt% SiO2

0.1–1000

25

1.5

0.1

50

2 wt% SiO2

0.1–1000

25

5

0.13

50

0.1 wt% SiO2 0.3 wt% SiO2 0.5 wt% SiO2

0.1–1000 0.1–1000 0.1–1000

25 25 25

2.2 2.9 2.8

2 2 2

50 50 50

– 0.2 wt% Cellulose 0.3 wt% Cellulose 0.5 wt% Cellulose 1 wt% Cellulose 2 wt% Cellulose 3 wt% Cellulose 5 wt% Cellulose 8 wt% Cellulose

0.1 wt% SiO2 0.3 wt% SiO2

40 mm cone and plate

Brookfield spindle Viscometer (LVDV-II SC4–34 + + Pro) Julabo, F12-ED

AR-G2 rheometer/capillary breakup extensional

40 mm cone-and-plate

–

–

MCR501, Co. Anton-Paar + Peltier temperature control

50 mm cone and plate 2 degrees angel/plate and plate

viscoelastic properties:0.052 mm, dynamic 1.0 mm

Anton Paar Rheometer Physica MCR 301

50 mm coneand-plate

–

17–52 17–52 17–52 17–52 17–52 17–77

0.157 0.089 0.035 0.025 0.01 0.25

0.045 0.033 0.015 0.012 0.005 0.033

7–67

0.28

0.031

[81]

56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56 56

[43]

[45]

80–160

2.9

0.035

80–16

3

0.025

50

[82]


ethanol ammonium nitrate n‑propyl ammonium nitrate ethyl ammonium nitrate ethyl ammonium formate dimethylethyl ammonium formate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑butyl‑3‑methylimidazolium nitrate 1‑ethyl‑3‑methylimadolium acetate 1‑ethyl‑3‑methylimadolium acetate

[83]

935

(continued on next page)

936

Table 1 (continued) Full name

Additives




Shear rate range


Temperature Initial STEADY-STATE viscosity VISCOSITY

Fixed shear rate

s−1

o

o

s−1

C

(Pa·s)

(Pa·s)

C

(Pa·s)

References

(Pa·s)

1 wt% SiO2 2 wt% SiO2 0.1 wt% SiO2

0.1–1000 0.1–1000 0.1–1000

25 25 100

2.1 2 0.008

2 2 0.01

50 50 50

0.3 wt% SiO2

0.1–1000

100

0.1

0.012

50

0.5 wt% SiO2

0.1–1000

100

0.35

0.013

50

1 wt% SiO2

0.1–1000

100

2.5

0.016

50

2 wt% SiO2

0.1–1000

100

6

0.02

50

0.1 wt% SiO2 0.3 wt% SiO2 0.5 wt% SiO2 1 wt% SiO2 2 wt% SiO2 0.1 wt% SiO2

0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000

100 100 100 100 100 200

0.015 0.018 0.015 0.015 0.02 0.03

0.013 0.013 0.013 0.013 0.015 0.0025

50 50 50 50 50 50

0.3 wt% SiO2

0.1–1000

200

0.2

0.003

50

0.5 wt% SiO2

0.1–1000

200

0.6

0.0035

50

1 wt% SiO2

0.1–1000

200

3

0.004

50

2 wt% SiO2

0.1–1000

200

8

0.045

50

0.1 wt% SiO2 0.3 wt% SiO2 0.5 wt% SiO2 1 wt% SiO2 2 wt% SiO2 0.1 wt% SiO2

0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000

200 200 200 200 200 25

0.0075 0.0038 0.029 0.011 0.0065 0.06

0.0025 0.0025 0.003 0.0026 0.0026 0.07

50 50 50 50 50 50

0.3 wt% SiO2

0.1–1000

25

0.04

0.07

50

0.5 wt% SiO2

0.1–1000

25

0.028

0.07

50

1 wt% SiO2

0.1–1000

25

0.027

0.06

50

2 wt% SiO2

0.1–1000

25

0.12

0.09

50

0.1 wt% SiO2

0.1–1000

25

0.003

0.005

50

0.3 wt% SiO2

0.1–1000

25

0.004

0.006

50

0.5 wt% SiO2

0.1–1000

25

0.008

0.0065

50

1 wt% SiO2

0.1–1000

25

0.007

0.007

50

2 wt% SiO2

0.1–1000

25

1

0.009

50

10–10,000 10–10,000

75 75

0.28 0.3

0.28 0.017

– n‑octylpyridinium iodide s‑butyl‑3‑methylmethimidazolium hexafluorophosphate

Gap

AR-G2 stress-controlled rheometer

4 mm cone and plate


1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium tetrafluoroborate 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide 1‑hexyl‑3‑methylimidazolium bis(trifluoromethyl Sulfonyl)imide


– [80]

n‑octylpyridiniumbistriflimide 3‑ethyl‑1‑methylmethimidazoliumdiethylphosphate 1‑butyl‑3‑methylimidazolium chloride 1‑ethyl‑3‑methyl‑imidazolium bistriflimide 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate

1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate

1‑allyl‑3‑methylimidazolium chloride








1‑allyl‑3‑methylimidazolium chloride 1‑allyl‑3‑methylimidazolium chloride




HAAKE RS6000 Rheometer (Germany)

TA AR2000 stress-controlled rheometer

TA AR2000 stresscontrolled rheometer

coaxial cylinder sensor system (Z41 Ti)

25 or 40 mm parallel-plate geometry

40 mm parallel-plate geometry

–

600 μm

800 μm

75 75 75 75

0.13 0.09 0.09 0.019 0.235 0.234

0.13 0.095 0.07 0.002 0.231 0.221

0.1–1000

0.249

0.225

0.1–1000

0.253

0.275

0.1–1000

0.292

0.225

0.1–1000

0.292

0.229

0.1–1000 0.1–1000

25 25

0.245 0.31

0.25 0.24

0.1–1000 0.1–1000

35 35

0.16 0.21

0.14 0.135

0.1–1000 0.1–1000

45 45

0.09 0.125

0.1 0.098

0.01–100

25

160

39

0.01–100

25

400

16

0.01–100

25

2000

110

0.01–100

25

7500

200

0.01–100

25

3500

120

0.01–100

25

2500

80

0.01–100

25

1000

300

0.01–100

25

5000

50

0.01–100 0.01–100

2.4 3.1

1 1.7

0.01–100

3.7

2.3

0.01–100

4.8

2.9

0.01–100

6

3.5

[44]

[84]


1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium hexafluorophosphate

[85]

937

– 0.02 wt% F-MWCNTs 0.04 wt% F-MWCNTs 0.06 wt% F-MWCNTs 0.08 wt% F-MWCNTs 0.1 wt% F-MWCNTs – 0.01 wt% pristine F-MWCNTs – 0.01 wt% pristine F-MWCNTs – 0.01 wt% pristine F-MWCNTs 7 wt% microcrystalline cellulose MCC 9 wt% microcrystalline cellulose MCC 11 wt% microcrystalline cellulose MCC 14 wt% microcrystalline cellulose MCC 16 wt% microcrystalline cellulose MCC 17 wt% microcrystalline cellulose MCC 18 wt% microcrystalline cellulose MCC 19 wt% microcrystalline cellulose MCC – 0.1% dissolving pulp cellulose (DPC) 0.2% dissolving pulp cellulose (DPC) 0.3% DPC dissolving pulp cellulose (DPC) 0.4% dissolving pulp cellulose (DPC)

10–10,000 10–10,000 10–10,000 10–10,000 0.1–1000 0.1–1000


938

Full name

Additives









1‑ethyl‑3‑methylimidazolium bis(trifluoromethyl sulfonyl)imide 1‑butyl‑3‑methylimidazolium tetrafluoroborate

1‑butyl‑3‑methylimidazolium tetrafluoroborate


0.5% dissolving pulp cellulose (DPC) 0.6% dissolving pulp cellulose (DPC) 0.8% dissolving pulp cellulose (DPC) 1% dissolving pulp cellulose (DPC) 1.5% dissolving pulp cellulose (DPC) 2% dissolving pulp cellulose (DPC) 3% dissolving pulp cellulose (DPC) 5 wt% hydrophilic silica 5 wt% hydrophilic silica 8 wt% hydrophilic silica 10 wt% hydrophilic

Physica MCR301, Anton Paar


25 mm,50 mm cone-and-plate

Gap

–



Shear rate range


Temperature

Initial STEADY-STATE viscosity VISCOSITY

Fixed shear rate

s−1

o

o

(Pa·s)

s−1

C

(Pa·s)

(Pa·s)

0.01–100

7

4

0.01–100

10

4

0.01–100

18

7

0.01–100

30

10

0.01–100

70

15

0.01–100

270

18

0.01–100

1500

50

0.1–1000

22,000

0.6

0.1–1000

0.58

0.55

0.1–1000

0.7

1.9

0.1–1000

1.5

6

C

References

(Pa·s)

[66]


Table 1 (continued)


1‑(2‑hydroxyethyl)‑3‑methylimidazolium bis (trifluoromethane sulfonyl)amide n,n-diethyl-n-methyl-N-2-methoxyethylammonium tetrafluoroborate 1-ethyl-3-methylimidazolium tetrafluoroborate

1-(2-hydroxyethyl)-3-methylimidazolium bis (trifluoromethane sulfonyl)amide 1‑butyl‑3‑methylimidazolium tetrafluoroborate

1‑ethyl‑3‑methyl‑imidazolium acetate 1‑ethyl‑3‑methyl‑imidazolium acetate 1‑ethyl‑3‑methyl‑imidazolium acetate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate ethyl‑methylimidazolium ethylsulfate

–

–

Physica UDS200 from Paar Physica

cone-plate geometry (MK23)

0.1–1000

3.5

25

0.1–1000

3.6

1.5

0.1–1000

0.95

1.1

0.1–1000

0.22

0.29

0.1–1000

1.7

0.3

0.1–1000

150

1

0.1–1000

40

0.42

–

50 μm

20–130 20–130 20–130 100–1000 100–1000 100–1000 100–1000 0.1–1000 0.1–1000 0.1–1000 0.1–1000 1–1000 1–1000 1–1000 1–1000 1–1000

25 40 60 80 27 40 60 80

0.09 0.07 0.04 0.039 10 10 10 10 0.9 7 7.2 11 0.08

0.08 0.06 0.038 0.02 0.2 0.09 0.055 0.04 0.08 0.1 0.1 0.2 0.085

6000 32,000 13,000

50 600 700

[86]

[48]

27–87

0.122

0.022


1-ethyl-3-methylimidazolium tetrafluoroborate

silica 15 wt% hydrophilic silica 5 wt% hydrophilic silica 5 wt% hydrophilic silica 5 wt% hydrophilic silica 5 wt% hydrophopic silica 5 wt% hydrophopic silica 5 wt% hydrophopic silica 10 wt% cellulose 12 wt% cellulose 16 wt% cellulose – – – – 30 wt% Fe2O3 30 wt% Fe2O3 30 wt% Fe2O3 30 wt% Fe2O3 20 wt% Fe2O3 30 wt% Fe2O3 35 wt% Fe2O3 40 wt% Fe2O3 –

939

940

Table 2 Overview on the rheological characterization and experimental setups for shear flow behaviors for varies tailor-made Natural Deep Eutectic Solvents. Full name

Additives

Rheometer specification Model

– – – – – – – – – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O 25 wt% H2O – 5 wt% H2O 10 wt% H2O 15 wt% H2O 20 wt% H2O

QCM/Rotational Viscometer (RV)

–

Viscosity Vs Shear rate Gap

–


References

Shear rate range

Temperature Initial Viscosity

Steady-state Viscosity

Temperature

Initial Viscosity

Steady-state viscosity

Fixed shear rate

s−1

o

(Pa·s)

o

(Pa·s)

(Pa·s)

s−1

C

(Pa·s)

C 27–87 27–87 27–87 27–87 27–87 27–87 27–87 27–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87 17–87

0.4 0.44 2.5 3 5.5 5 12.9 0.5 0.4 0.3 0.27 0.22 0.18 0.15 0.51 0.37 0.33 0.25 0.18 0.15 3.5 1.52 0.9 0.45 0.15 0.1 4 1.53 1 0.45 0.3 0.15 10.55 3 1.7 1.55 1.2 1.2 0.6 0.35 0.27 0.16 0.12 0.07 7.6 1.5 1.2 1.1 1 0.5 7.5 1.62 1.45 1.3 1.1

0.15 0.1 0.3 0.32 0.5 0.6 2.0 0.55 0.15 0.14 0.12 0.1 0.1 0.09 0.13 0.12 0.11 0.1 0.09 0.08 0.35 0.3 0.2 0.18 0.08 0.06 0.25 0.22 0.2 0.18 0.15 0.09 1.7 1 1 1 1 1 0.105 0.095 0.09 0.08 0.075 0.065 1.1 1 1 0.55 0.55 0.5 1.25 1.2 1.1 1 1

[87]


choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (QCM) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (QCM) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (QCM) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (RV) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + ethylene glycol (1:2) (QCM) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (RV) choline chloride + glycerol (1:2) (QCM) choline chloride + glycerol (1:2) (QCM) choline chloride + glycerol (1:2) (QCM) choline chloride + glycerol (1:2) (QCM) choline chloride + glycerol (1:2) (QCM) choline chloride + glycerol (1:2) (QCM) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (RV) choline chloride + malonic acid (1:1) (QCM) choline chloride + malonic acid (1:1) (QCM) choline chloride + malonic acid (1:1) (QCM) choline chloride + malonic acid (1:1) (QCM) choline chloride + malonic acid (1:1) (QCM) choline chloride + malonic acid (1:1) (QCM) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (RV) choline chloride + urea (1:2) (QCM) choline chloride + urea (1:2) (QCM) choline chloride + urea (1:2) (QCM) choline chloride + urea (1:2) (QCM) choline chloride + urea (1:2) (QCM)


25 wt% H2O 25 25

choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + urea (1:2) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + xylose (1:1)

– – – – – 2 wt-% NiCl2 2 wt-% NiCl2 2 wt-% NiCl2 2 wt-% NiCl2 2 wt-% NiCl2 5 wt-% NiCl2 5 wt-% NiCl2 5 wt-% NiCl2 5 wt-% NiCl2 5 wt-% NiCl2 – – – – – – – – – – 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O

25 25 – –

Anton Paar MCR 102 (Modular Compact Rheometer)

CP 40 Cone and Plate

Controlled-stress Paar Physica MCR300, Germany QCM/Rotational Viscometer (model MC 20)

Concentric cylinder geometry (CC10) –

Kinexus Prot, MAL1097376, Malvern

Parallel Plate geometry (20 mm of diameter) (PU20 SR1740

0.1

–

1–1000 1–1000

25 25

0.4 0.2

0.4 0.2

1–1000 1–1000 0.1–1000 0.01–1000

25 25 23 23

10 3 280 350

10 3 30 3.5

–

1

17–87 20–70 20–70

1 0.65 0.32

0.5 0.1 0.1

20–70 20–70

2.26 1.8

0.2 0.22 [35]

20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 20–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80

450 110 35 12 5 2 1.1 0.8 0.6 0.4 300 80 26 9 4 2 1 0.7 0.5 0.4 70 20 8 3.8 1.9 1 0.8 0.5 0.4 0.38 25 10 4.8 2.6 1.5 0.8 0.6 0.5

430 90 30 10 4 2 1 0.65 0.4 0.2 250 80 25 9 3.5 1.5 0.9 0.45 0.3 0.18 60 19 8 3 1.5 0.8 0.42 0.28 0.19 0.13 21 10 4.1 2 1.5 0.7 0.45 0.25

[88]

1.5 0.75 0.39 0.32 0.21 1.67 0.91 0.49 0.35 0.2 5 1.3 0.3 0.2 0.15

0.05 0.05 0.05 0.05 0.05 0.1 0.1 0.1 0.1 0.1 0.12 0.12 0.12 0.12 0.12

[89]

[13]

941



choline chloride + urea (1:2) (QCM) benzyltributylammonium chloride + phenol (1:3) benzyltributylammonium chloride + ethylene glycol (1:3) benzyltributylammonium chloride + lactic acid (1:3) benzyltributylammonium chloride + glycerol (1:3) citric acid + glucose (1:1) choline chloride + citric acid (1:1)

942

Table 2 (continued) Full name

Additives

Rheometer specification Model

5 wt% H2O 5 wt% H2O – – – – – – – – – – – – 1 wt% chitin

chlorine chloride + urea (1:2) choline chloride + ethylene glycol (1:2) chlorine chloride + glycerol (1:2) chlorine chloride + urea (1:2) choline chloride + ethylene glycol (1:2) chlorine chloride + glycerol (1:2) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1)

– – – 10 wt% H2O 10 wt% H2O 10 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 0 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O 1 wt% H2O

Anton Paar Rheometer Model MCR 302

Cone and plate (CP)

Anton Paar, Physica MCR 301 rheometer USA

Parallel plate PP50/P-PTD200 geometry (50 mm diameter) Parallel plate PP50/P-PTD200 geometry (49.971 mm

Anton Paar, Physica MCR 301 rheometer USA

Malvern rheometer, model kinexus Prot

cone-plate (40 mm diameter)

Viscosity Vs Shear rate Gap

0.104

0.1

0.75

–


References

Shear rate range

Temperature

Initial Viscosity

Steady-state Viscosity

Temperature

Initial Viscosity

Steady-state viscosity

Fixed shear rate

s−1

o

(Pa·s)

(Pa·s)

o

(Pa·s)

(Pa·s)

s−1

C

0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0–200

90 100 35 35 35 55 55 55 75 75 75 90 90 90 60

0.4 0.3 1 8 8000 0.4 0.38 1 0.3 0.18 0.1 0.15 0.15 0.5 1.39

0.2 0.12 0.45 0.4 8.1 0.08 0.07 0.035 0.042 0.03 0.02 0.03 0.025 0.015 0.4

10–50 10–50 10–50 10–50 10–50 10–50 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100

25 25 25 25 25 25 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80

550 200 550 20 200 20 – 2000 350 100 27 10 5 2 1 0.7 2000 600 110 35 15 7 3 1.8

350 70 400 10 40 4 – 2000 348 900 25 10 4 2 1 0.6 1950 600 100 30 15 7 3.5 1.8

C

27–97 27–97 27–97

0.8 6 7000

0.2 0.2 0.1

[70]

[90]

[33]

[34]


choline chloride + xylose (1:1) choline chloride + xylose (1:1) choline chloride + phenylacetic acid (1:2) choline chloride + phenylacetic acid (1:3) choline chloride + phenylacetic acid (1:4) choline chloride + phenylacetic acid (1:2) choline chloride + phenylAcetic acid (1:3) choline chloride + phenylacetic acid (1:4) choline chloride + phenylacetic acid (1:2) choline chloride + phenylacetic acid (1:3) choline chloride + phenylacetic acid (1:4) choline chloride + phenylacetic acid (1:2) choline chloride + phenylacetic acid (1:3) choline chloride + phenylacetic acid (1:4) choline chloride + thiourea (1:2)


chlorine chloride: glycerol (1:2) choline chloride + ethylene glycol (1:2) chlorine chloride: citric acid (1:1) chlorine chloride: citric acid (1:1)

chlorine chloride: lactic acid (1:1) chlorine chloride: lactic acid (1:1) chlorine chloride: lactic acid (1:1) chlorine chloride: lactic acid (1:1) chlorine chloride: lactic acid (1:1) chlorine chloride: malic acid (1:1) chlorine chloride: citric acid (1:1) chlorine chloride: fructose (1:1) chlorine chloride: p-toluensulfonic acid (2:1) chlorine chloride: trichloracetic acid (2:1) chlorine chloride: monochloroacetic acid (2:1) chlorine chloride: propionic acid (2:1)

1 wt% H2O 1 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 3 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O 5 wt% H2O – – – – – – – – –

– 7.8 wt% PVA 9.8 wt% PVA

– – – – – – – – – – – –

0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100 0.1–100

90 100 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

1 0.5 350 90 20 9 5.5 2 1.5 0.8 0.6 0.4 68 25 10 4.5 2.8 1.5 1 0.7 0.5 0.4

1 0.5 300 80 18 9 6 3 1.8 0.8 0.6 0.25 60 20 9 4 2 1 0.8 0.55 0.4 0.2

TA Instruments AR-G2 rheometer

Cone and plate arrangement with a cone of 40 mm radius

–

Malvern rheometer, model kinexus Prot

Parallel plates, with a diameter of 20 mm 50 mm Cone and Plate

–

0.1–1000 0.1–1000

25 25

0.35 0.56

0.42 0.58

[92]

0.104 mm

0.01–100 0.01–100 0.01–100 0.01–100

25 45 65 85

1.6 1.4 2 0.58

0.4 0.18 0.08 0.04

[33]

Anton Paar Rheometer Model MCR 302

Anton paar Viscometer SVM 3000

–

–

17–97 17–97

1.2 0.41

0.1 0.09

17–97

0.1

0.05

15–95 15–95 15–95 15–95 7–67 7–67 7–67 7–67

0.28 3.5 1000 0.36 1.83 1 0.2 0.1

0.08 0.3 0.95 0.1 0.1 0.09 0.05 0.05

[91]


chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride + glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) chlorine chloride: glucose (1:1) choline chloride + xylose (1:1) chlorine chloride: sucrose (1:1) chlorine chloride: citric acid (1:1) chlorine chloride: tartaric acid (1:1) betaine: citric acid (1:1) betaine: tartaric acid (1:1) chlorine chloride: urea (1:2)

[93]

943

944


2. Shear flow behaviors The viscosity of a fluid is defined as the quantification of the resistance to deformation under shear stress that is mainly due to the internal friction within the fluid [19], where parallel fluid layers move at varied velocities. The mathematical representation can be shown as following: τ¼η

du dy

ð1Þ

where τ represents shear stress, η is the coefficient of dynamic viscosity and (du/dy) is the shear rate. Fluids are mainly classified into two distinguished categories as Newtonian fluids and non-Newtonian fluids. Newtonian fluids show constant viscosity behavior over the change in shear or external force. Well-defined Newtonian liquids are also known for their low molecular weight (e.g. water, glycerol, acetone). On the other hand, nonNewtonian fluids have complete dependency on the imposed shear rate, the reflected behavior of shear can either be thickening or thinning, which can be represented by Fig. 1. In most studies, IL are commonly known for their non-Newtonian behavior but some studies have shown their ability to become Newtonian fluids [19,20]. On the other side, research conducted on NADES has shown that they mainly behave as Newtonian fluids and they are similar to ILs when they act as nonNewtonian fluids. To investigate the flow behavior under varied shear rates, a rheogram is used to evaluate the flowability of a NADES/ILs through its vastly dependency on the apparent viscosity [20]. This parameter is best to define the non-Newtonian behavior of NADES/ILs i.e. shear thinning or shear thickening. As the shear rate increases, materials tend to illustrate a non-uniform viscosity profile at isothermal conditions [21]. As a result, a successful viscosity profile characterization can describe the flow properties and deformation (Fig. 2), which may indicate their expected field applications and uses. In this review, we study the behavior of different combinations for NADES/ILs i.e. changing the cation and anion in ILs while varying the hydrogen bond donor (HBD) and holding the hydrogen bond acceptor (HBA) constant for NADES. A combination of all the recent efforts conducted on all the solvents were extracted, grouped, and categorized in order to visualize the main factors that can potentially influence the change in apparent viscosity over high shear rate. Due to the relevance of Imidazolium based ILs and Natural Deep Eutectic Solvents rheology on process design and performance, many studies on the apparent viscosity are published in literature. Tables 1 and 2 give an intensive overview of key research works, which mainly highlight the initial viscosity and steady-state viscosity for the solvents with different scenarios. It shows the type of ILs/ NADES with the type of additive studied, the rheometer details (brand, geometry configuration, size), shear rate range, temperature range and the fixed shear rate for the apparent viscosity against temperature measurements if found. 2.1. Ambient Temperature 2.1.1. NADES Recent works by various research groups have highlighted the cons of ILs over the past few years, and these works have showed that a new system of solvents called DES can be considered as alternatives due to their highly promising properties and characteristics, which in turn can be considered to replace amines, and other organic solvents. These novel solvents are produced by combining HBA and HBD in a mixture at known proportions [22]. When HBD and HBA combined, it leads to depression in melting point reaching to values close to ambient temperature [23]. Such melting point depression allows DES to be handled in liquid state for the desired process applications [24]. In addition, DES can be modified or produced by using natural products yielding better

environmental profiles with low toxicity and high biodegradability [25–27], which are abbreviated as NADES. Characteristic examples of NADES include eutectic mixtures of amino acids or sugars with common organic acids [28,29]. The advantage of working with NADES is that they are abundant in nature and much cheaper to produce in comparison to other exotic solvents. Biodegradable and biocompatible nature of NADESs makes them easy to handle and recycle or dispose cheaper than other alternative competitors [30]. However, besides all advantages the main benefit of using NADES over DES (or even ILs) is that the ability to prepare NADES at very low toxicity levels. In recent studies it was found that there are some known examples of NADES in living organisms and it is believed to lead the biosynthesis of poorly watersoluble metabolites and macromolecules in the aqueous environments [31]. The advantage in the flow behavior of NADES at room temperature over traditional solvents is that, they can be used and operated in different chemical industries [32]. The lack of NADES shear flow measurements at room temperatures made it a difficult task for many researchers to analyze the flow behaviors of different NADES. The focus of this study is to highlight a series of NADES based on a choline chloride (ChCl) as HBA that is coupled with alternating HBD. Reported data showed that the rheological behavior of different mixtures of NADES at room temperature is showing a universal trend depending on the detailed microstructure of the HBD and HBA. Solvents such as citric acid + glucose and choline chloride + citric acid at 1:1 mol ratios (Fig. 3) showed a shear-thinning behavior under a controlled shear rate of 0.1–1000 s−1 at 23 °C. The apparent viscosity initially fluctuated at ranges from 0.1 s−1 to 1 s−1 from 450 to 230 Pa·s, but as it approached 1 s−1, a Newtonian plateau at a viscosity of approximately 6 ± 2 Pa·s was observed and the viscosity became independent of the shear rate. Furthermore, Altamash et al. [18] studied four different low viscosity NADES for the use in gas sorption processes of CO2 and N2, which are choline chloride + lactic acid, choline chloride + citric acid, choline chloride + malic acid, choline chloride +lactic acid, and choline chloride + fructose. Nevertheless, the shear flows have shown a common shear thinning behavior among all the solvents at 25 °C under a shear rate domain of 0.01–1000 s−1 at atmospheric pressure. The absolute values of apparent viscosity showed that alternating the HBD has a significant effect on the application of the NADES. The viscosity of choline chloride + citric acid was significantly the highest among the rest, followed by choline chloride + malic acid which had viscosity values of 1000, 40 Pa·s respectively. Conversely, chlorine chloride + lacctic acid and chlorine chloride + fructose showed a relatively lower viscosity (0.4 and 0.6 Pa·s) in comparison with the other two systems. Although this work showed the initial viscosity values for the mentioned systems, yet the apparent viscosity profile for only the choline chloride + lactic acid was represented in a rheogram (Fig. 3). Das et al. [33] discussed the use of choline chloride + ethylene glycol, choline chloride + urea, choline chloride + glycerol NADES with evenly prepared mole ratios of 1:2 for the extraction of k-carrageenan from Kappaphycus alvarezii. Despite the rheogram presented for the NADES mentioned, the focus was not intensively qualitative. Although Das et al. [33] was one of the few to study the flow behaviors of more than one type of NADES, however, they did not approach the rheological explanation of the NADES behaviors at room temperature. Furthermore, the study of this set of NADES was one of the most successfully prepared solvents in terms of low viscosity. Initial viscosities at 10 s−1 for anhydrous choline chloride + ethylene glycol, choline chloride + urea, choline chloride + glycerol (Fig. 3) was measured as 0.16, 0.42 and 0.35 Pa·s respectively, the change in apparent viscosity after increasing the shear rate to 50 s−1 was decreased to 0.04, 0.13 and 0.12 Pa·s respectively. As a result, the apparent viscosities measured in this study were successfully the lowest values obtained in literature. Even though that the general conclusion about NADES is that they behave like nonNewtonian liquids (more towards solid-like behavior) at room temperature under varied shear rate, yet Aroso et al. [13] also elaborated on a


Fig. 3. log-log scale representation of the apparent viscosity (Pa·s) vs shear rate (s−1) for Choline Chloride Citric Acid (1:1) [35], Choline Chloride Lactic Acid (1:1) [18], Choline Chloride xylose (1:1) [13], Choline Chloride Glucose (1:1) [34], Choline Chloride glycerol (1:2) [37], Choline Chloride Urea (1:2) [37], Choline Chloride Ethyl Glycol (1:2) [37]at ambient temperature condition.

series of HBD with choline chloride; xylose, glucose (Fig. 3) and sucrose have shown that they are very viscous liquids with a Newtonian behavior. Rheological characterization of this set of NADES showed a constant trend in the viscosity profile, which was completely independent to applied shear rate. The study offered a sample rheogram for chlorine chloride + xylose (1:1) showing a constant change in the viscosity profile of 116 Pa·s. In another published work, Aroso et al. [34] presented the shear flow of Choline Chloride + glucose (1:1), similar to the conditions of the previously studied NADES combinations. In both papers, the general discussion was to set an agreement on the general behavior of NADES is that they are Newtonian liquids, independent of shear rate, and with very high viscosity at room temperature conditions. In contrast, Paula et al. [35] has discussed their disappointment of trying to apply rheological characterization for a selection of NADES such as citric acid + sucrose (1:1), citric acid + glucose (1:1), and choline chloride + citric acid (1:1, 2:1), as most of them exhibited a solid-like behavior at room temperature. Likewise, Aroso et al. [13] also discussed his disability of performing rheological characterization on choline chloride + citric acid (1:1) and choline chloride + tartaric acid (2:1, 1:1, 1:2) due to the less mobility and high viscosity of the sample stating that the viscosity has exceeded the equipment limits (N10,000 Pa·s). Yan et al. [36] reported that the chemical nature of the component such as the halide salt type, mole ratio, and the HBD are the main reasons of high viscosity at room temperature, which bring us to the conclusion that NADES are solid-like material at room temperature conditions. 2.1.2. ILs ILs have become an interest in several scientific and industrial sectors for several reasons such as their exclusive chemical and physical properties (i.e. low vapor pressure, high thermal stability, nonvolatile). In addition, ILs consists of a cation and an anion and they might exist in liquid state at room temperatures (RTILs). Since the beginning of the last decade, some ILs (e.g. imidazolium based) have drew attention in the field of applied research due to their high biodegradability, poor biocompatibility (considering large list of ILs), mild toxicology, some level of unsuitable physical properties (e.g. high viscosity) and high production cost at bulk quantities for certain ILs [38–40]. Alternation of anions and cations can yield up to 1018 different combinations, thus making these solvents “true designer solvents” [41,42]. Due to this potential, both academic and industrial interest on these fluids has been exponentially on the rise during the last few years.

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Fig. 4. log-log representation of the apparent viscosity vs shear rate of pure imidazolium ILs [bmim][TF2N] [52], [bmim][PF6] [43], [bmim][NO3] [43], [bmim][PF6] [44], [emim] [Ac] [45], [emim][EtSO4] [48], [emim][Tso] [53] at ambient temperature conditions.

2.1.2.1. Imidazolium based – pure. Pure RTILs show diverse behaviors under the regions of a flow curve for different combinations, according to the attached active group on the cation. Similarly, NADES rheology at room temperature flow regimes showed different behaviors from Newtonian to non-Newtonian by changing the HBA only. Since ILs are made up of discrete cations and anions, the possibility of combinations can be engineered as per the required application. According to rheologists, it was observed that the anion structure of the studied ILs has a far stronger effect on the rheological properties than analogous changes to the cation. In literature, we have mainly found that the most common ILs are imidazolium-based cations. The anions that were looked at the most were fluorinated such as bis (trifluromethyl sulfonyl) imide [NTF2] and hexafluorophosphate [PF6] or non-fluorinated such as nitrate [NO3], acetate [Ac], and ehylsulfate [EtSO4]. As shown in the Fig. 4, the [PF6] anion was measured in two different studies. The first study [43] measured the viscosity over a restricted domain from approximately 10 to 60 s−1, where the viscosity was found constant at almost 0.27 Pa·s. Although the measurement domain for this study was less than any others, yet in the second study [44], which studied the use of different imidazolium based ILs in the field of functionalized multi-walled carbon nanotubes. Apparent viscosity was measured for pure [PF6] based ILs (Fig. 4) again on a shear interval from 0.1 to 1000 s−1. In this specific study, the measured viscosity showed constant change due to the Newtonian behavior of this combination, where it proves that the viscosity of pure imidazolium liquids is unique and independent of the value for the applied shear rate. Furthermore, Moosavi et al. [43] conducted shear flow behavior of 1‑butyl‑3‑methylimidazolium nitrate [bmim][NO3] (Fig. 4) at the shear rate from 10 to 60 s−1, the shear flow for this combination showed similar behavior to the hexafluorophosphate based anion studied in parallel, where the viscosity was stable all over the domain at a value around 0.16 Pa·s. It can also be noticed that the behavior of 1‑ethyl‑3‑methylimidazolium acetate (Fig. 4) had Newtonian behavior [45], the steady shear viscosity trend showed its reliability through its low water content and high purity, which showed consistency and agreement with pure acetate based ILs [46,47]. The rheological characterization of Ethyl‑methylimidazolium Ethylsulfate (Fig. 4) was studied under room temperature conditions [48]. The flow behavior of this imidazolium-based ILs showed similar Newtonian behavior to the rest of the illustrated shear flow profiles, mostly at high shear rate ranges (b 100 s−1), as the viscosity varied from 0.05–0.04 Pa·s. On the other hand, 1‑ehyl‑3‑methylimidazolium tosylate [emim][TSO] (Fig. 4)

946


showed a relatively different flow behavior under 0.001 to 600 s−1, the viscous system exhibited a shear thinning behavior with increasing the shear rate. The decrease in viscosity for the tosylate based ILs showed a strong and dramatic decay at low shear rates, where the viscosity dropped from almost 7 to 0.7 Pa·s. The shear thinning region was showed in previous studies for several other imidazolium-based ILs [48–51]. The viscosity eventually reached steady-state at moderate and high shear rates, where it was approximated to be almost 10 times less than it was in the shear thinning phase. As the shear rate continuous to increase, the viscosity remains constant; the reason behind this was explained as the remaining intermolecular interactions have full resistance to any external load due to the breakdown in the intermolecular bonds at early shear rate stages such as the hydrogen bond, which causes the viscosity to diminish. In addition, [52] molecular dynamic simulations using non-equilibrium molecular dynamics were performed in order to understand room temperature imidazoliumbased ILs interactions in the molecular level. The structure of 1‑butyl‑3‑methylimidazolium bis(trifluorometilsulfonil)imide (Fig. 4) showed that the hydrogen bonds have a major effect on shear viscosity for ILs. The generated trend represented a relatively different behavior at very low shear rates in comparison with other experimentally determined measurements, where an unusual shear-thinning region was developed at approximately 0.001 s−1. In conclusion, it can be witnessed that Imidazolium-ILs in general, are less viscous than NADES accordingly to the processed and presented data in this review. 2.1.2.2. Imidazolium based – with additives. While pure ILs exhibited a Newtonian fluid behavior at room temperature, the addition of a solute or flow additive can significantly change the flow regime, where both shear thinning and thickening are likely to appear as the applied external force increases. [48,54,55] Many researchers showed that the cationic part of the ILs has a significant impact on rheological behavior, it has also been proved that the addition of additives can change the behavior of ILs dramatically (i.e. from either a shear thinning or natural non-Newtonian behavior). The addition of flow additives to ILs have emerged over the past decade, such additives include natural polymers of various kinds such as silk [56], keratin [57], chitin [58,59], lignocellulose (wood) [60–62] and cellulose [63,64]. In addition, other additives such as nanoparticles, nanofluids, and hematite have also been used to investigate their influence on shear flow behaviors in different

Fig. 5. log-log representation of the apparent viscosity vs shear rate of imidazolium based ILs with different additives [bmim][Cl] + 0.2 wt% Cellulose [65], [bmim][Cl] + 0.2 wt% Cellulose + 3 wt% H2O [65], [bmim][BF4] + 5 wt% hydrophilic Silica [66], [bmim][BF4] + 5 wt% hydrophobic Silica [66], [bmim][PF6] + 0.01 wt% Pristine F-MWCNTs [44], [emim][Ac] + 8 wt% Cellulose [45], [emim][EtSO4] + 40 wt% Fe2O3 [48] at ambient conditions.

applications. Many researchers showed that in addition to the cationic modifications on ILs, additives showed significant effect on the shear flow behavior of ILs. Haward et al. [45] also performed compensative studies on solutions of cellulose dissolved in 1‑ethyl‑3‑methylimidazolium acetate ILs. They showed that the viscosity of these solutions determined throughout regular viscosity measurement also exhibited shear-thinning behavior over a shear rate domain from 0.1 to 100 s−1. The apparent viscosity was relatively higher than that of the one studied by Nazari et al. [65], which can be due to the effect of adding a few percentages of water to the mixture. Similarly, Ueno et al. [66] demonstrated that the shear flow of the dispersions of hydrophilic and hydrophobic silica nanoparticles investigations on 1‑(2‑hydroxyethyl)‑3‑methylimidazolium bis(trifluoromethane sulfonyl)amide (Fig. 5). Adding the hydrophilic silica to the ILs showed a Newtonian flow behavior with constant change in the viscosity all over the shear rate domain. However, hydrophobic silica (Fig. 5) changed the flow regime from a Newtonian to non-Newtonian behavior, which represents the magnificent effect of the dispersion of hydrophobic silica nanoparticles on ILs. Wang et al. [44] studied the functionalized multi-walled carbon nanotubes 1‑butyl‑3‑methylimidazolium hexafluorophosphate nanofluids at different concentrations (Fig. 5) and they showed that the shear viscosity of the hybrid ILs was lower than that of the pure ILs (Fig. 5) all over the shear rate domain and the difference was even more significance at higher shear rates. Wang et al. explained such behavior due to the attribution of the self-lubrication of the modified nanotube. A detailed study was conducted to show the effect of adding hematite to ethylmethylimidazolium ethylsulfate [48] (Fig. 5), the concentrated suspensions of the particles showed non-Newtonian flow behavior similar to the trend shown by [45,65,66]. 2.2. Temperature dependency of NADES The general analogy to NADES systems with increasing temperature is that the viscosity trend decreases with increase in the shear rate. Yan et al. [36] elaborated on the transport phenomena explanation for NADES systems, through his study on the usage of NADES as a heat transfer fluid. The main reason behind the significant decrease in viscosity with temperature increase is a result of the structural breakdown caused by the thermal expansion of the structure and shearing effect.

Fig. 6. log-log representation of the apparent viscosity vs shear rate of different NADES: chorine chloride + glucose (1:1) [34], choline chloride + xylose (1:1) [13], choline chloride + phenylacetic Acid (1:2) [70], choline chloride + phenylacetic acid (1:3) [70], choline chloride + phenylacetic acid (1:4) [70], choline chloride + lactic acid (1:1) [18] at high temperature conditions.


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Fig. 7. a–f: log-log representation of the apparent viscosity vs shear rate of different NADES systems at incremented temperatures for: choline chloride + phenylacetic acid (1:2), (1:3), and (1:4) [70], choline chloride + lactic acid (1:1) [18], chorine chloride + glucose (1:1) [34], choline chloride + xylose (1:1) [13].

They also observed that at such conditions, the mixture starts to converge and physically behave as the pure HBD. In other studies, at high temperature conditions, the molecules flow smoothly and become less viscous because of the decrease in their internal resistance [67–69]. In a series of studies, Aroso et al. [13,34] measured the apparent viscosity at a fixed shear rate from 0.1–100 s−1 under a series in the range of temperatures of 60–100 °C for choline chloride + glucose and choline + xyylose (1:1) (Fig. 6) (Fig. 7e,f). As the temperature increased, the initial viscosity (at 0.1 s−1) ranged from 10.34–0.68 Pa·s for the glucose system, and from 2.29–0.42 Pa·s for the xylose system. At high shear rate (100 s−1), the difference in magnitude for the viscosity reduced significantly, this is due to the structural breakdown for all the systems. Despite the low temperature that consequently hindered the flow behavior, changing the HBD of the system, and the enclosure of water, had significantly reduced the high viscosity of choline chloride-based NADES, where the viscosities of NADES ranged from 0.05 Pa·s to as high as 2000 Pa·s (Fig. 4). However, the difference was minimized when it came to high temperature conditions, the differences ranged from as little as 0.01 Pa·s to 0.7 Pa·s over the same shear rate mentioned earlier. Hence, if the application required being low temperature, attention should be given to the donor. On the other hand, if the application is at high temperature, such dependence is not significant. As the shear rate began to achieve 100 s−1, the change in viscosity was minimal reaching steady-state conditions. It can be concluded from this study that at high shear rate, the flow behavior for both tested NADES systems is independent of temperature and shear rate. Furthermore, Altamash et al. [18] reported an extensive work on thermo-physical NADES characterization for a group of NADES systems at different temperatures for their promising use as cheap, and environmentally green absorbents in CO2 capture. In addition to their study on four-different choline chloride

1:1 based NADES, they extended their work to study the mole ratio effect under the effect of different temperatures for a solitary NADES system [70]. In their work, choline chloride + phenylacetic acid system was measured at varied temperatures (35,55,75, and 90 °C). The apparent viscosity at continuous shear rate increase from 0.01 to 100 s−1 was decreasing at all the applied temperatures. Their findings were similarly consistent with the general trend of NADES systems investigated in the literature. Moreover, the effect of mole ratio for the phenylacetic acid exhibited a dual behavior notice, for mole ratios of (1:2) and (1:3) under an intermediate shear rate of 10 s−1, the flow behavior showed usual shear-thinning due to the breakdown of its structure. Although most of the studied look at the shear flow behavior of NADES, Altamash et al. [70] was the only researcher in literature to conduct a study on the different molar ratio behavior for a single system, which shows the lack in rheological properties for such an effect. The explained trends previously explained can be shown in Fig. 7a, b, c. Based on this conclusion, Ghaedi et al. [67] showed a matching agreement with these findings, who had conducted a group of studies based on six similar based HBA of phosphonium using three molar ratios of 1:4, 1:10, and 1:16 under a temperature range from 25 °C to 70 °C. They have showed that the increase in temperature lowers the viscosity with the increasing quantity of HBD in a NADES system. On the other hand, the 1:4 showed an unusual semi-solid material behavior at 35 °C. Furthermore, when the viscosity as a function of temperature was measured for the 1:4 mol ratio, a viscosity value of over 6000 Pa·s was initially exhibited. However, with increasing the temperature, when the melting point (55 °C) was achieved, a gel-like material began to form and the viscosity dramatically dropped to 1.2 Pa·s. In addition, Altamash et al. [70] came to another interesting conclusion, in which they elaborated on the molar ratio effectiveness on NADES viscosity as a function of temperature,

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Fig. 8. log-log representation of the apparent viscosity vs shear rate of different NADES systems with different hydration ratios at room temp (20–25C): choline chloride + glucose (1:1) [34], choline chloride + glucose (1:1) + 5% H2O [34], choline chloride + xylose (1:1) [13]+ choline chloride + xylose (1:1) + 5% H2O [13], choline chloride + glycerol (1:2) [37], choline chloride + glycerol (1:2) + 10% H2O [37], choline chloride + urea (1:2) [37], choline chloride + urea (1:2) + 10% H2O [37], choline chloride + ethylene glycol (1:2) [37], choline chloride + ethylene glycol (1:2) + 10% H2O [37].

the molar ratio becomes an independent factor on viscosity at higher temperature ranges, while it significantly affects the behavior at low temperature conditions. This inference will have a significant application in many applications that require low viscosity at high temperatures to minimize pumping costs and practical usage in solvent applications that will increase the mass transport rates [67]. Choline chloride + lactic acid (Figs. 6 and 8d), choline chloride + citric acid, choline chloride + malic acid, choline chloride + malic acid, and choline chloride + fructose also validated their explanation to the behavior of the NADES. This latter result is in keeping with the previous studies showing that the viscosity is decreasing with temperature for all the NADES systems present in literature.

25 Pa·s at 5 wt% of added water content respectively. In comparison to higher temperatures, at 100 °C, the effect of hydration was negligible, as the change between the four water percentages only altered the viscosity from 1 Pa·s to 0.3 Pa·s. Dai et al. [76] showed that the strong hydrogen bonding between the HBA and HBD are weakened down, as expected due to the re-establishment of hydrogen bonding mapping within the system, when water molecules are added. This is explained by the fact that the presence of any small amount of water molecules tends to form hydrogen bonds that decreases the viscosity that acts as plasticizer. Likewise, the choline chloride + xylose (1:1) system showed the same behavior over different water content under elevated shear rates. At room temperature, the shear viscosity showed a moderately lower order of magnitude than the glucose at 0 wt% water, where the viscosity was found approximately to be 110 Pa·s. At 1, 3, and 5 wt% water content, the viscosity decreased to 80, 22, 10 Pa·s, respectively. On the other hand, at higher temperatures under the same shear rate, the temperature had insignificant effects on the shear viscosity, as the viscosity was only lowered from 0.3 Pa·s to 0.2 Pa·s at 100 °C for this system. Das et al. [33] considered three different NADES systems as discussed previously and adding 10 wt% of H2O (Fig. 8). All the NADES showed non-Newtonian behavior in all cases. Viscosity values showed a gradual decline as the shear rate interval was increased. Shear flow behaviors mainly showed that the anhydrate NADES had a lower degree of flowability, which makes them a stiff-like solvent over the measured domain. On the other hand, hydrated NADES showed a relatively higher degree of flowability and less stiff behavior, which can conclude that these solvents can be used in applications that are water-content depended such as pumping. Consequently, hydrated NADES were favored over the non-hydrated NADES, as the hydrated were more superior in quality and more effective in the extraction. 2.4. Hydration effect on ILs The viscosity of dry Imidazolium based ILs have generally shown consistency in their rheological shear flow behavior, exhibiting a Newtonian response at different shear rates [43–45,48,53,65,77]. The phenomena of adding less viscous fluids such as water to ILs systems has shown significant decrease in apparent viscosity [78,79]. Several studies were conducted to describe various water-miscible imidazolium based ILs effect on purely imidazolium based ILs. In a study by Burrell et al.

2.3. Hydration effect on NADES Simple inclusion of water to flowing systems such as mineral oil makes it a versatile solution in several applications. The addition of water as a co-solvent to a NADES system can be considered as an impurity when handled in commercial applications that consequently lead to a significant change in the nature of a NADES. For instance, through moderate addition of water to a NADES, the phase separation ability and its absorption capability can be controlled [71–73]. In addition, hydration of NADES has a significant effect in the creation and the shape control of nanoparticle synthesis [74]. Water addition has also been shown to negatively affect the solubility of CO2 on NADES with the increase of water percentage [71]. The interaction of water with binary tailor-made NADES system gives it an additional interest to study the mechanisms involved between them in terms of molecular structure and the physiochemical properties, as these interactions clearly show its importance in different applications [75]. In the same study by Aroso et al. [13,34], a specific rheological investigation was reported for the choline chloride + xylose (1:1) and choline chloride + glucose (1:1) (Fig. 8) systems at different water contents of 0, 1, 3, and 5 wt% at various different temperatures. At null water content, the relatively vast shear viscosity for glucose showed a constant Newtonian behavior. The viscosity was initially reported as 2000 Pa·s. As the water content increased in the system, the shear viscosity began to significantly decreased with shear especially at room temperature, where the viscosity was found to decrease to 400 Pa·s at 1 wt%, 90 Pa·s at 3 wt%, and

Fig. 9. log-log representation of the apparent viscosity vs shear rate of different Imidazolium based ILs systems with different hydration ratios: (HOEt)2NH·AcOH + 0 wt% H2O [20 °C] [80], (HOEt)2NH·AcOH +8 wt% H2O [20 °C] [80], [emim][Ac] + 0 wt % H2O [20 °C] [77], [emim][Ac] + 5 wt% H2O [20 °C] [77], [bmim[Cl] + 0.2 wt% cellulose + 0 wt% H2O [20 °C] [65], [bmim[Cl] + 0.2 wt% cellulose + 3 wt% H2O [20 °C]] [65] at ambient conditions.


[80], they had investigated the impact of hydration on diethanolamine acetic acid ((HOEt)2NH·AcOH) (Fig. 9). The effect of adding water on this system had shown the expected trend, they showed that with the increase of 3 wt% water content, the rheological behavior of the dry ILs binary system changed from non-Newtonian shear thinning behavior, to a Newtonian plateau (Fig. 9). Moreover, Burrell et al. also studied the effect of different molar equivalent ratios of water on the same ILs. The shear viscosity for (HOEt)2NH·AcOH at 0.125,0.50, 1.00, 2.00, 4.00, 8.00 wt% showed diverged responses. The addition of amounts less than and around 3 and 4 wt% equivalents of water produced Newtonian responses. With the increment of water content to N3–4 wt% equivalents, non-Newtonian shear thickening was observed. The effect of small dilution volumes of water inferred that no cohesive aggregate interaction in the structure were witnessed, but reduced the amount of aggregates. Olsson et al. [77] studied the effect of adding 5 wt% water on pure 1‑Ethyl‑3‑methylimidazolium acetate ([emim][Ac]) (Fig. 9). The viscosity of a 10 wt% concentrated cellulose solutions slightly decreased when 5 wt% of water was added to the system. However, it is crucial to mention that there was absolutely no change in the flow regime with the addition of water. On the other hand, Nazari et al. [65] findings on 1‑Butyl‑3‑methylimidazolium chloride ([bmim][Cl]) 0.2 wt% cellulose and 3 wt% were different in terms of the change in the viscous profile. The flow regime dramatically changed when 3 wt% of water was added, to exhibit a non-Newtonian shear thinning behavior from a Newtonian flow behavior (Fig. 9). 3. Viscoelasticity Elasticity is the result of a fluid at zero stress reduction to partially recover and to behave as a liquid or an elastic solid [94]. The elastic properties of the materials are described by the storage modulus (G′, ratio of elastic stress over strain) and loss modulus (G″, the ratio of viscous stress over strain) are corresponding to the amount of energy stored and dissipated during deformation. The effects of these two moduli are combined into the complex modulus (G*) as shown in the following equation G ¼ G0 þ iG″

ð2Þ

The viscoelastic material possesses complex dynamic viscosity (η*). η ¼

G ω

ð3Þ

where ω is the angular frequency. Based on the literature reviewed, viscoelastic properties have shown a relatively lower attention of studies in recent literature. Viscoelastic oscillatory measurements were used to avoid any destruction of the networks formed for the structured solvents such as ILs and NADES and to measure the elastic viscoelastic properties of the solvents. The differences between G′and G″ are used as indication whether the solvents are more like viscous liquids or like solid materials and this crucial parameter in pumping and processing such structured solvents. Although many researchers chose to describe NADES and ILs using thermo-physical rheological characterization [13,36,43,95], yet the focus in most publications are concerned with shear flow behavior only, while paying less attention to importance of the viscoelastic properties of NADES/ILs. A possible explanation behind this could be a result of instrument limitation, since rheometers are only capable of measuring the change of storage and loss modulus with different parameters such as time, temperature, shear stress and shear rate. Besides, if possible, researchers should consider adopting such measurement in order to explore its application and potential in NADES and ILs as it might lead to better understanding of their rheological behavior in oscillatory mode. In this review, it is proposed that viscoelastic measurements for oscillatory rheology to be a useful tool. This type of measurements is more relevant for

949

ILs and NADES with high viscosities, which are more challenging in liquid transportation or pumping. An overview on the rheological characterization and experimental setups for oscillatory behaviors for various tailor-made imidazolium based ILs and NADES are shown in Table 3, featuring the main outcomes and highlights of the viscoelastic studies. 3.1. Viscoelastic behavior of ILs Oscillatory measurement has proved to be a useful analysis method to determine the elastic properties of ILs, which can provide a meaningful insight to the technical matters, such as pumping and CO2 capture. With better understanding of the dynamic behavior, engineers and scientists can incorporate these parameters into their designs to improve their use in different field applications. Bharmoria et al. [96] revealed that the G′N G″ along indicating that the elastic behavior was dominant over the viscous behavior, where they discussed the frequency dependency of G′ and G″ of agarose ionogels that were prepared at different compositions of reciprocal binary mixtures of protic/aprotic ILs 2hydroxyethylammonium formate/1‑Butyl‑3‑methylimidazolium chloride ([HEA][HCOO]/[C4mim] [Cl]). The relatively higher difference between G′ and G″ for all the combinations indicates that the general trend of these ionogels represents a solid like behavior. Furthermore, the strain dependency of G′ and G″ from 0.1 to 100% at ω = 100 rad/ s was examined in order to determine the microstructure strength of these gel-like ILs. Results showed that all these ionogels had a linear viscoelastic behavior, which show that the gel's microstructure can withstand and resist deformation, even at high % strain. The strength of these increases showed a significant increase with the increase of [HEA][HCOO] concentration. The attribution of such behavior is a result of the enhancement between the interactions of the hydrogen bonding between the agarose hydroxyl groups by the ions of [HEA][HCOO]. Wang et al. [44] investigated different oscillatory studies on the viscoelasticity behavior of 1‑butyl‑3‑methylimidazolium hexafluorophosphate ([Bmim][PF6]) nanofluids that contain functionalized multi-walled carbon nanotubes (F-MWCNTs) at different concentrations. The G″ was always found to be greater than G′ over the frequency range of 0.01–100 rad·s−1 of a pure [Bmim][PF6] and a [Bmim][PF6] + F-MWCNTs 0.1 wt%, which indicate that they mainly showed viscoelastic liquids. The addition of F-MWCNTs showed an increase in G′ to an extant with the increase in angular frequency, while no spectacular change was observed herein for G″. Moreover, an inflection point was noticed in the G″ for both the pure and fabricated ILs at a critical angular frequency of 2 and 8 rad·s−1, which was theoretically explained by the NADES structure that exists in the pure [Bmim][PF6] or the nanofluid. Haward et al. [45] displays the characteristic shear and extensional rheology of dilute to semi-dilute solutions of cellulose in the IL 1-ethyl-3-methylimidazolium acetate at room temperature. The oscillatory shear tests showed that G″ was significantly greater than G′, which indicates that this combination exhibits a viscously dominated behavior. The crossover point where G″ reaches its peak and becomes larger than G′, can be defined as the instantaneous moment where the applied mechanical force overtakes the inter particles forces and the material starts to exhibit a degree of flow ability (yielding), which is a hallmark of the soft-glassy materials. This phenomenon was achieved at high concentrations of cellulose only (c = 8 wt%) at almost ω ≈ 30 rad/ s, which shows the dominant elastic response in the material onset. Furthermore, Pamies et al. [53] looked at the effect of concentration, types of carbon nanotubes, and temperature on the viscoelasticity of 1‑ethyl‑3‑methylimidazolium tosylate and its dispersions with aligned and nonaligned multi-walled carbon nanotubes (MWCNTs). It was found that none of the ILs resulted in a gel transition at ambient temperature. However, when temperature was raised, the results showed that pure ILs and the EMIMTsO-MWCNTs 1 wt% dispersion represented a temperature-induced gelation. Nonetheless, adding relatively smaller amounts of MWCNTs inhibits the formation of gel-

950

Table 3 Overview on the rheological characterization and experimental setups for oscillatory behaviors for various tailor-made Imidazolium based ILs and Natural Deep Eutectic Solvents (NADES). Ambient conditions (°C)

Angular frequency range

Strain amplitude (%)

Observations and conclusions

Measurements (the figures below are shown in the papers, however only g′ vs g″ vs angular frequency were explained)

References (According to the new one)

1 wt% celluose +0.25 wt% water

20

0.01–1000 rad/s

0.01

G″, G′, Complex viscosity vs angular frequency

[65]

1‑ethyl‑3‑methylimidazolium acetate (EMImAc) and 1‑butyl‑3‑methylimidazolium chloride (BMImCl)

1 wt% celluose

20 and 80

0.01–1000 rad/s

0.01

G″,G′, Complex viscosity vs angular frequency

[65]

1‑ethyl‑3‑methylimidazolium tosylate (EMIMTsO)

–

25,50,75,100

0.01–1000 Hz

0.20

G′G″ vs angular frequency

[53]

1‑ethyl‑3‑methylimidazolium tosylate (EMIMTsO)

aligned and nonaligned 25, 100 multiwall carbon nanotubes (MWCNTs)

0.01–1000 Hz

0.20

G′G″ vs Angular Frequency

[53]

1‑benzyl‑3‑methylimidazolium bis[(trifluoromethane)sulfonyl] amid

–

−32,-37,-41,-45,-48, 0.01 to 50 -51,-54,-56,-58 Hz

0.01

dilute to semi-dilute solutions of cellulose (0.1 wt% b c b 8 wt%)

25

0.1–100 rad/s

low strain amplitude

G′, G″ vs angular frequency, van Gurp−Palmen plot, complex viscosity vs angular frequency/shear rate G′,G″ vs angular frequency, complex viscosity vs angular frequency

[98]

1‑ethyl‑3‑methylimidazolium acetate (EMIAc)

1‑ethyl‑3‑methylimidazolium chloride 1‑ethyl‑3‑methylimidazolium flouride

–

90

0.01–100 1 s−1

1,5,10

G′, G″ vs Shear Stress, G′, G″ vs Angular Frequency, deformation % vs time

[82]

1‑hexyl‑3‑methylimidazolium bis(trifluoromethylsulfonil) imide

0.3 wt% SiO2 + 0 M,1,2 dispersion of silica nanoparticle

25

0.1–100 rad/s

0.10

G′,G″ vs Angular frequency

[83]

1‑ethyl‑3‑methylimidazolium bromide

3–6 wt% Polyacrylonitrile (PAN)

50,60,70,75

0.1–100 s-1

1.00

1) Adding 0.25 wt% water to the solutions for both G′ and G″ the moduli became independent of frequency in the low ω limit with G′ ≫ G″ 2) with higher water content and cellulose content, the moduli are flat expands to higher frequencies 3) adding small quantities of water (0.25 wt%) revealed dramatic changes in the solution LVE upon 1) Annealing both the dehydrated samples at 80 °C for 20 min resulted in a solidlike, elastic response, with a long relaxation time for 1.0 wt% cellulose solution vanishes 2) the absorbance of water to IL/cellulose solutions creates noncrystalline cellulose network-like aggregates that are responsible for low frequency elastic response without annealing 1) When the frequency is increased, the storage and loss moduli increase but in different manners 2) G″ shows a potential growth with the frequency, while G′ first keeps constant and finally there is a rapid increase from 10−4 to 1 Pa at all temperatures 3) The viscous behavior prevails over the elasticity of the sample and G″ N G′ at 25oc and 50oC 4) cross-over at two different frequency ranges occurred of the two moduli happens and sol-gel transitions are observed at 75 and 100? Ci 1) All MWCNTs at low concentrations showed that the loss modulus is predominant over the storage modulus all over the frequency range 2) The addition of low quantities of MWCNTs diminishes the values of G″ and this effect is stronger for the aligned nanotubes. 3) At high frequencies, the values of G′ and G″ crossover 4) When temperature is raised, the values of the loss modulus decrease, as seen for the pure IL, while the values of the storage modulus barely show a temperature effect 1) the ionic liquid shows a glassy response at low temperatures or high frequencies and flow behavior at high temperatures or low frequencies 2) The loss modulus goes through a maximum as the temperature decreases through glass transition 1) At lower cellulose concentrations, G″ is much greater than G′, indicating viscously dominated behavior; however, for c ≥ 3 wt%, G′ approaches G″ at high frequencies. 2) At c = 8 wt%, crossover is achieved for ω ≈ 30 rad s − 1, indicating the onset of a dominant elastic response in the material. 1) The elastic properties are higher for 1‑ethyl‑3‑methylimidazolium chloride than the viscous properties 2) 1‑ethyl‑3‑methylimidazolium fluoride shows a point of intersection at an angular frequency of 40 s−1 3) At lower deformation (1% and 5%) the storage modulus is nearly constant and above the loss modulus, which increases with increasing angular frequency 1) the loss modulus was higher than the storage modulus for all angular frequencies suggesting the presence of stable dispersions over the whole interval 2)Dispersions are considered “stable” when the nanoparticles do not show a tendency to agglomerate into a 3D network 3) gelation occurred when the critical angular frequency was the lowest frequency where the viscous behavior of a solution could be detected 4) the high values of critical angular frequency or even gelation over the entire frequency range clearly showed the trend that it was impossible to obtain stable dispersions at high-temperatures and/or -nanoparticle concentrations 1) Both G′ and G″ increase with increasing the PAN concentration 2) The crossover frequency of G′ to G″ is shown to decrease as the concentration is increased

Complex viscosity vs strain, Complex viscosity vs angular velocity, G′G″ vs Angular velocity, reduced complex viscosity vs reduced angular velocity

[99]

Ionic 1-ethyl-3-methylimidazolium liquids acetate (EMImAc)

[45]


Additive

Name

–

25

0.01–100

1 Hz

1) G″ is always larger than G′ over the whole frequency range, and G″ and G′ also follow a scaling law with exponents of 1

1‑butyl‑3‑methylimidazolium hexafluorophosphate

0.1 wt% functionalized multi-walled carbon nanotubes (F-MWCNTs) 9 and 16 wt% concentrated solutions of microcrystalline cellulose (MCC)

25

0.01–100

1 Hz

25

0.1–100 rad/s

15.00

1‑allyl‑3‑methylimidazolium chloride ([amim]Cl) was

–

30

0.1–100 rad/s

20.00

1‑allyl‑3‑methylimidazolium chloride ([amim]Cl) was

Cellulose of 0.1–3.0 wt %

30

0.1–100 rad/s

20.00

1‑(2‑hydroxyethyl)‑3‑ methylimidazolium bis(trifluoromethane sulfonyl)amide

5 wt% hydrophobic silica 5,8,10,15wt.% hydrophilic silica

25

0.1–100 rad/s

0.1–0.5

1‑butyl‑3‑methylimidazolium tetrafluoroborate (BMIBF4)

Pristine single-walled carbon nanotubes formed gels after being ground

25

0.01–1000 rad/s

0.01,0.1,1

choline chloride+ urea 1:2 choline chloride+ ethylene glycol 1:2 choline chloride+ glycerol 1:2

0% Hydrated 10% Hydrated

25

0.05–800 1 0.1% and frequency s−1 0.01 Hz

Betaine malic acid Betaine lactic acid b-Alanine malic acid b-Alanine lactic acid

–

25

0.1–100 rad/s

1) G″ is always larger than G′ over the whole frequency range, and G″ and G′ also follow a scaling law with exponents of 1.36 2) G′ of the nanofluid is increased to some extent with the increment of the angular frequency while there is no obvious variation for G″ 1) For the solutions with MCC concentration below 9 wt%, G′ is always smaller than G″ and no crossover is found within the detected frequency range. 2) as the cellulose concentration increases from 11 to 14 wt%, G′ b G″ only occurs at low frequencies and a crossover appears at a higher frequency. 3) the concentration from 7 to 14 wt%, the crossover frequency evidently moves to lower values with increasing cellulose concentration 4) the crossover frequency first moves to lower values and then moves back to higher values with increasing cellulose concentration, which indicates that most cellulose chains are aligned or oriented to reduce chain entanglements when the cellulose concentration is above 14 wt%. 1) both G′ and G″ increase monotonously with increasing frequency, and the increases are approximately proportional to ω2 and ω in the experimental frequency range, respectively, which is similar to the viscoelastic behavior of polymer solutions in the low-frequency range 2) the much higher G′ values of [amim]Cl in the same frequency range may reasonably indicate that [amim]Cl should be considered as a “structured liquid” rather 1) It can be observed that G′-ω curves for the dilute solutions (concentration is below 0.5 wt%) undergo two stage increases with different slopes except [amim]Cl. With increasing concentration, the G′-ω curve shifts to lower frequencies without curve shape changed 2) In the semi-dilute unentangled regime (0.5 wt% b C b 1.5 wt%), the storage modulus is lower than the loss modulus, and the slopes of both moduli in the high-frequency region gradually decrease. 3) When the concentration increases to 1.5 wt%, the storage modulus and loss modulus become close, and the slopes are both approximate to 0.5 in the high-frequency region 4) at a concentration of C N 1.5 wt%, there is a crossover in the low-frequency region, showing the typical behavior for entangled polymer solutions. 1) dispersion containing 5 wt% of the hydrophilic silica in [C2mim][NTf2] exhibits a frequency-independent elastic modulus (G′) that is higher than its viscous modulus (G ″) by 1 order of magnitude; the system behaves as a soft solid (gel) 2)that particle aggregation does not occur even in concentrated dispersions containing 15 wt% of the silica nanoparticles 3) the dispersions in the ILs behave as soft- solids (gels) formed by the space-spanning silica aggregates, as G′ is higher than G″ without a considerable dependence on frequency 1) At an applied strain of 0.01%, the dynamic storage modulus G' curve of the bulky gel IL showed a plateau region in the frequency dispersion curves, indicating the existence of an elastic network structure in the system 2) At 0.1%, the G′ curve still showed a plateau region. However, when the strain was increased to 1.0, the system began to behave like a critical gel, where the G' and G" values both dropped 1) Using pure NADES as solvents showed viscous liquid behavior in the angular frequency range of 500–650 s-1. 2) After the crossover of the moduli, the store modulus started to became predominant over the loss modulus indicating elastic nature of the gels at higher frequency range 1) The greater difference in the values of G″ and G′ (e.g. G″ ≫ G′) indicating presence of more flow components in the gels making the gels behave like viscous liquid and as the G′ → 0 the material behave as ideal viscous flow behavior 2)The values of G′,G″, and η* decreased as the temperature increased for all NADES systems as expected for the shear thinning materials and this is mainly due to the changes in the interaction forces between the hydrogen bond donor and hydrogen accepter of the NADES and due to the thermal expansion

1‑allyl‑3‑methylimidazolium chloride (AMIMCl)

NADES

0.10

G′,G″ vs angular frequency, complex viscosity vs angular frequency G′,G″ vs angular frequency, complex viscosity vs angular frequency

[44]

G′,G″ vs Angular Frequency, complex viscosity vs Frequency, oscillatory shear vs shear rate

[84]

G′,G″ vs angular frequency

[85]

G′,G″ vs angular frequency

[85]

G′,G″ vs Angular Frequency, G' vs volume fraction, G' vs wavelength

[66]

G′,G″ vs Angular Frequency

[100]

G′,G″ vs angular frequency, Complex viscosity vs temperature

[33]

G′,G″ vs angular frequency, complex viscosity, G, G″ vs temperature

[17]

[44]


1‑butyl‑3‑methylimidazolium hexafluorophosphate

951

952


like structures. However, when temperature was raised, a temperatureinduced gel formation is witnessed for pure ILs and concentrated dispersions, with higher G′ and G″ values in the case of the aligned MWCNTs. However, these three-dimensional networks are not found in the diluted dispersions. Similarly to [44,45] the ILs presented showed values of the G″ higher than the G′, meaning that they behave like a typical fluid. No crosslink between both moduli was spotted for neither the pure IL nor the ones in dispersions. Therefore, one can conclude that different combination of ILs showed different viscoelastic behaviors, which are important factors that must be considered to improve their use in different field applications. 3.2. Viscoelastic behavior of NADES Mukesh et al. [97] prepared choline chloride and orcinol with polymerized 0.35, 0.5 and 1% v/v of 2‑hydroxyethyl methacrylate (HEMA). Results revealed that the nature of this polymerized gel combination was highly stretchable. When HEMA and NADES solution (unpolymerized mixture) were measured, the magnitude of G″ N G′, meaning that the formed mixture was viscous. On the other hand, the polymerized mixture showed values of G′ ≫ G″, indicating a true gel formation. Moreover, the stretching/flexible behavior was studied by studying the recovery of G′ of the ion-gel obtained for the 1:0.35 NADES:HEMA. The sample was loaded under varied stain at 1 Hz frequency for 300 s, while strain was applied to the sample. The strain effect was continued on the ion gel to study the fracture on the sample. It was shown that both the moduli remained almost constant, meaning that the ion gels were not affected by strain and unfractured. As a result, this showed how this combination of polymerized NADES can be an

excellent flexible and durable nature ion gel with a high stretchable nature. Das et al. [37] studied the viscoelasticity of three different deep eutectic solvents. The time dependency measurements for all the kC gels showed a gel like behavior (G′ ≫ G″) during the entire period of extraction, where the difference between the G′ and G′′ was relatively high for the case the kC gels extracted using choline chloride + glycerol (1:2) and hydrated choline chloride +ethylene glycol 1:2. Moreover, concluded that the presence of the NADES enhanced less stiffness and better viscoelasticity in comparison with other conventional exaction methods like water as a solvent. Furthermore, the crossover of G′ and G″found as a result of increasing the angular frequency for all the kC gel systems, which spots the attention of how weak the gels are, whereas the G″and predominate over the G′ in a wide frequency range, which shows that the presence of different flow components in the tailored gel that are viscous liquids at lower frequencies. However, at higher frequency ranges, the G′ started to become predominant in manganite over G″ indicating an elastic nature of these gels. Furthermore, Altamash et al. [17,18] looked at the interaction forces between different pure combinations of HBA (choline chloride, B-alanine, and betaine) with different natural organic HBD (lactic acid, malic acid, citric acid, and fructose) with 1:1 M ratios using oscillatory viscoelasticity. Throughout their studies, they have shown a consistent agreement between all the combinations in terms of the solvent behavior even at high temperatures, where the values of G′′ were always higher than G′ over the applied frequency from 0.1–100 rad/s. As a result, this shows that all the solvents were viscous liquids at all temperatures. The differences between G′′ and G′ revile the presence of the initiative flow components within the gel structure and as the storage modulus diminishes (G′ → 0) an ideal viscous flow behavior (i.e. less stiffness) is witnessed. However,

Fig. 10. a–c: semi-log representation of G',G" (mPa), and η*(mPa·s) vs Angular frequency (rad/s) for and alanine + lactic acid [17], alanine + malic acid [17], betaine + lactic acid [17], betaine + malic acid [17] NADES systems at ambient conditions with a fixed frequency from 0.1 s−1, while d: shows the combination of both G′ and G″ as a function of angular frequency.


953

Table 4 Arrhenius model parameters for different ILs and Natural Deep Eutectic Solvents (NADES). Arrhenius equation IL/NADES Ionic liquids

ηo (109 × Pa·s)

Ea (kJ/mol)

References

10.8 29.5 18.6 2.87 3.03 3.66 9.81 0.04 3.05 0.0008 0.017 0.018 5.9 × 10−5 3.9 × 10−5 5.5 × 10−5 3.1 × 10−6 4.3 × 10−5 6.9 × 10−6

41.8 38.6 40.2 25.89 26.39 25.96 24.23 56.8 44.9 71.9 63.9 71.02 91.52 104.5 96.15 102.08 97.79 101.94

[53]

1‑ethyl‑3‑methylimadolium tosylote 1‑ethyl‑3‑methylimadolium tosylote + nonaligned MWCNTs 1‑ethyl‑3‑methylimadolium tosylote + aligned MWCNTs ethyl‑methylimidazolium ethylsulfate + wt 20% Fe2O3 ethyl‑methylimidazolium ethylsulfate + wt 30% Fe2O3 ethyl‑methylimidazolium ethylsulfate + wt 35% Fe2O3 ethyl‑methylimidazolium ethylsulfate + wt 40% Fe2O3 benzyltributylammonium chloride + phenol (1:3) benzyltributylammonium chloride + ethylene glycol (1:3) benzyltributylammonium chloride + lactic acid (1:3) benzyltributylammonium chloride + glycerol (1:3) choline chloride xyolose @ 1:1:0 choline chloride glucose @ 1:1:0 choline chloride sucrose @ 1:1:0 choline chloride citric acid @ 1:1:0 choline chloride tartaric acid @ 1:1:0 betaine citric acid @ 1:1:0 betaine tartaric acid @ 1:1:0

Deep eutectic solvents

at high frequency and room temperature, the sample that contain malic acid as a HBD showed values of G′ (7.2 × 104 Pa for betaine + malic acid and 3.3 × 104 Pa for alanine + malic acid) higher than G″in comparison with lactic acid based magnitudes (2.3 × 102 Pa for B-alanine + lactic acid and 1.1 × 102 Pa for betaine + lactic acid) (Fig. 9a–d). Moreover, they have concluded that with the increase in temperature for the NADES, all the systems showed shear thinning behaviors over the applied frequency as a result of the interaction forces between the HBA and HBD forces and the thermal expansion. In conclusion, they elaborated on highly recommending choline chloride + lactic acid, betaine + lactic acid, B‑alanine + lactic acid, and choline chloride + fructose for CO2 applications since preheating or pumping of sorbents is required (Fig. 10). 4. Rheological models 4.1. Arrhenius equation The temperature dependency of the viscosity represents an exponential-like decay for most ILs and NADES, in order to account for

[48]

[88]

[13]

the overall effect of temperature, a governing equation known by the Arrhenius equation is mostly used to describe the flow resistance for both ILs and NADES under different temperatures, which can be defined as following: ln η ¼ ln η0 þ

EA RT

ð4Þ

In this equation η is the dynamic viscosity (106Pa · s−1) that is measured at each temperature,

is the viscosity parameter η0 (10 Pa · s) and also referred to as the pre-exponential factor in other references [53], E A is the activation energy of the flow (kJ · mol−1) Regarding to EA, Altin et al. [48] explained that this parameter enlightens the structural information of the ILs throughout their studies on suspension rheology of hematite in ILs and pure ILs, and they explained that the strong intermolecular forces between the ions resulted in larger values of E A for the suspension ILs with lower (20%wt. of Fe2O3) than the ones with higher (% 40 wt Fe2O3). Likewise, Pamies et al. [53] also showed that the addition of aligned 6

Table 5 Vogel-Fulcher-Tammann model parameters for different ILs and Natural Deep Eutectic Solvents (NADES). Vogel-Fulcher-Tammann equation

Ionic liquids


IL/NADES

ηo or A' (Pa·s)

B' (K)

T∞ or To (K)

References

2‑hydroxy ethylammonium acetate 2‑hydroxy diethylammonium acetate 2‑hydroxy ethylammonium propionate 2‑hydroxy ethylammonium lactate 2‑hydroxydiethylammonium lactate ethylammonium nitrate propylammonium nitrate ethylammonium formate ethanolammonium nitrate dimethylethylammonium formate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium nitrate benzyltributylammonium chloride + phenol (1:3) benzyltributylammonium chloride + ethylene glycol (1:3) benzyltributylammonium chloride + lactic acid (1:3) benzyltributylammonium chloride + glycerol (1:3) choline chloride p‑toluenesulfonic acid choline chloride trichloroacetic acid choline chloride monochloroacetic acid @ 1:1:0 choline chloride propionic acid @ 1:1:0

1.06 × 10−5 2.65 × 10−5 4.31 × 10−5 1.32 × 10−5 8.22 × 10−4 3.50 × 10−4 3.90 × 10−4 3.00 × 10−4 3.50 × 10−4 1.90 × 10−4 1.38 × 10−4 4.87 × 10−4 7.21 × 10−5 1.85 × 10−5 3.23 × 10−5 7.20 × 10−6 1.30 × 10−4 6.29 × 10−5 1.25 × 10−4 1.06 × 10−4

1663 1473 1406 1732 1014 588 676 564 655 584 942 571 748 1295 1046 1619 8478 1033 788 855

142 169 164 137 184 168 169 166 187 146 173 199 211 161 209 173 200 181 183 162

[95]

[81]

[43] [88]

[93]

954


Table 6 Ostward-de Waele Power-law equation model parameters for different ILs. Ostward-de Waele Power-law equation

Ionic liquid

IL/NADES

K (mPa·s)

n

References

1‑Butyl‑3‑methylimidazolium chloride 1‑ethyl‑3‑methyl‑imidazolium bistriflimid N‑octylpyridinium iodide N‑octylpyridinium bistriflimid 3‑ethyl‑1‑methylmethimidazoliumdiethylphosphate S‑butyl‑3‑methylmethimidazolium dibutylphosphate S‑butyl‑3‑methylmethimidazolium hexafluorophosphat S‑butyl‑3‑methylmethimidazolium dibutylphosphate 1‑butyl‑2‑ethyl thiotetrazolium diethyl phosphate diethanolamine acetic acid diethanolamine methylsulfonic acid diethanolamine formic acid Ethanediamine formic acid pyrrolidine acetic acid

96 19 273 126 92 816 305 100 48 5642 1766 784 115 38

0.99 0.98 1 1 1 0.93 0.98 1 1 1 0.98 0.99 1 1

[80]

and non-aligned multiwalled carbon nanotubes (MWCNTs) influence the activation energy of 1‑ethyl‑3‑methylimadolium tosylate, as these additives have the ability to enhance the capacity of dispersion to flow in comparison with pure ILs and eventually lowering the activation energy. On the other hand, activation energy for NADES systems implies that the degree of flowability is dependent on the constituent particles [88], in order for the solvent to flow, it must overcome the barrier energy of the EA, similarly to ILs, the higher EA generally describes the difficulty for particles to move. Furthermore, Aroso et al. [13] looked at the activation energy effect for choline chloride + xylose, results have shown that the activation energy also decreases with the increase of water content present in the system, as the substantially hydrogen bond interactions decrease. R is the universal gas constant (kJ · mol−1 · K−1) and T is the absolute temperature (K) (Table 4). It is also noteworthy to mention that the Arrhenius expression is a subclass of the general Vogel– Fulcher–Tamman (VFT), having T0 = 0. 4.2. Vogel-Fulcher-Tammann equation The general followability and transport property of ILs and NADES can also be modeled using The Vogel–Fulcher–Tamman (VFT), which is a temperature dependence fitting model that best describes the molecular interactions, such as the van der Waals type weak interactions and strong hydrogen bonding [95]. where the parameters (Table 5) of this model include; η: dynamic viscosity (Pa·s), η0/η∞/A′: limiting high-temperature viscosity (Pa·s), B′: parameter related to free activation energy (K), T:temperature (K), T0/T∞: vogel temperature (K). Cui et al. [93] used a slightly modified notation to describe the Vogel −Fulcher−Tammann, where they replaced the factor with activation energy and the KB using EA/KB. B0

η ¼ A0 eT−T 0 D

η ¼ η0 e

τ ðγÞ ¼ Kγn

ð8Þ

4.4. Power law equation Based on coupling theory, the following form was formulated, where and η0, TX, γ are parameters that depend on the material [80]. The value of γ is expected to be within 2–4 for most glass forming liquids. Glassforming materials are those for which crystallization is avoided and produce a super cooled liquid. Further cooling eventually results a material as a disordered solid in a glassy state. It is noteworthy to mention that no regression modeling was performed on NADES for this particular model (Tables 7–9). η ¼ η0

T−T X −γ TX

ð9Þ

4.5. Litovitz equation Also known as the Macedo—Litovitz hybrid equation, which is used for the viscosity of liquids derived using statistical-mechanical arguments. The formulation is based upon the assumption that diffusion in liquids is governed by; (i). the presence of an adjacent free volume of certain size into which a molecule can jump and (ii) the acquisition of

ð5Þ

T0 T−T 0

η ¼ η∞ e

the range from 0 to 1, whereas shear thickening can be described if n N 1, conversely, shear thickening fluids exhibit an increase. By definition a Newtonian fluid has a power law value of n = 1 and the viscosity is constant across all shear rates. Shear thinning fluids have a lower apparent [48,80]. It is noteworthy to mention that no regression modeling was performed on NADES for this particular model.

ð6Þ

Ea K B ðT−T 0Þ

Table 7 Power Law model parameters for different ILs. Power law equation IL/NADES

ηo (Pa·s)

2‑hydroxy ethylammonium acetate 2‑hydroxy diethylammonium acetate 2‑hydroxy ethylammonium propionate 2‑hydroxy ethylammonium lactate 2‑hydroxydiethylammonium lactate 1‑butyl‑3‑methylimidazolium hexafluorophosphate 1‑butyl‑3‑methylimidazolium nitrate

0.0027 212.2 5.6 [95] 0.0593 178.9 8.5 0.0075 208.2 6.2

ð7Þ Ionic liquid

4.3. Ostwald-de Waele power-law equation _ Shear rate (s−1), n: Power K:Viscosity (Pa·s) for a given shear rate γ: law flow index (unitless). Both parameters must be determined from experiments (Table 6). For shear thinning of the product, the closer n is to zero, the values of n have a lower apparent viscosity and are in

Tx (K)

γ

References

0.0064 199.7 6.1 0.0011 255.3 3.6 0.0018 243 3.3 [43] 0.0016 251

2.7


955

Table 8 Litovitz model parameters for different ILs. Litovitz equation

Ionic liquids

IL/NADES

Ln(A/Pa·s)

(B/R) × 10−8/K3

References


−7.8 −7.7 −7.2 −7.6 −7.8 −7.1 −7.4

1.9 2.3 2.0 1.8 1.9 1.5 1.5

[95]

sufficient energy by the diffusing molecule to escape from the force field of its neighbors. [101] B

ð10Þ

η ¼ A eRT 3

where η: Viscosity (Pa·s), A: Fitting parameter (Pa·s), B: Fitting parameter (kJ · mol−1 · K−2), R: Gas constant (kJ · mol−1 · K−1), T: Temperature (K). 4.6. Ghatee equation This model is one of the recently developed equation that was aimed to fit and describe the temperature-dependent viscosity of ILs. The Ghatee equation consists of two parameters. It showed the best fit to the experimental data in comparison to the litvitz and the power law. It is noteworthy to mention that no regression modeling was performed on NADES for this particular model. ϕ 1 ¼aþbT η

ð11Þ

where its parameters consist of η: viscosity (Pa·s), ϕ: characteristic exponent (unitless) (ϕ = 0.3 for ILs), a: fitting parameter (Pa · s)−0.3, b: fitting parameter (Pa · s)−0.3 K−1, T: temperature (K) [95].

[43]

where τ represents the shear stress (mPa·s), τ0 is the yield stress (mPa), γ is the shear strain rate s−1, k is a dimensionless constant coefficient and n is the flow behavior index. [103] As shown in Table 10 it can be seen that a lower value of n is indication of a more non-Newtonian behavior or a shear thinning fluid. According to the extracted data of shows that the mixture is more Newtonian as n ~ 1.0 as the temperature and the concentration of PhOAc increased [70] where this comes to an agreement with other deep eutectic solvents. The values of n listed in Table 10 are significantly are the same, and all the n values in the tables are order of magnitude of 1, regardless to the additional decimal places. Therefore, 4.8. Bingham equation The Bingham equation describes the viscosity function and to estimate the dynamic yield stress values [18], basically implies that the material is solid-like at low rates and stresses [102]. In addition, this model accounts for the behavior of many shear-thinning materials at low shear rates, but the calculated value of τB depends on the shear rate ranges used for the extrapolation procedure [59] the Bingham model just takes into account the region with constant slope and in this case, it covers higher shear rates [103]. Another possibility is that the fluid behaves as a Bingham plastic, like for example toothpaste, in which the viscosity appears to be infinite until a certain value of shear stress is achieved [35] where the Bingham equation for non-Newtonian fluids is as following

4.7. Herschel-Bulkley equation The Herschel-Bulkley model is frequently used to calculate yield stress region by fitting the data from rheograms [102] or the region at low shear rates while the Bingham model just takes into account the region with constant slope and in this case it covers higher shear rates [103]. fits most flow curves with a good correlation coefficient, and for this reason, it is the most widely used model [59] However, one of the drawbacks of the Herschel-Bulkley equation is that it does not distinguish whether the observed change in viscosity is due to the change in time or shear stress since these two variables are changed simultaneously [103]. Furthermore, this model defines a fluid with three parameters and the model is mathematically described as τ ¼ τ0 þ ηoγn

ð12Þ

τ ¼ τ B þ ηB γ

ð13Þ

where τ represents the shear stress, τB is the Bingham yield stress and ηB is the Bingham plastic viscosity, γ_ is the shear rate. The magnitude of τB is a useful parameter that can be used as indicative of the amount of minimum stress required disrupting the networked structure in order to initiate the flow. A yield stress below τB for the mixture means that the mixture behaves as a rigid solid [18]. In general, the yield stresses of all NADES decreased with increasing temperature as expected for the shear thinning materials. The differences in the yield stress values are mainly due to the changes in molecular mobility, such as chain rigidity, interaction forces between the hydrogen bond donor and hydrogen accepter of the NADES and the molecular weight.

Table 9 Ghatee model parameters for different ILs. Ghatee equation

Ionic liquids

IL/NADES

a (Pa·s) -0.3

b (Pa·s)−0.3 K−1

References


−8.00 −7.24 −6.64 −7.46 −7.77 −6.65 −7.08

0.03 0.03 0.03 0.03 0.03 0.03 0.03

[95]

[43]

956


Table 10 Herschel-Bulkley model parameters for different ILs and Natural Deep Eutectic Solvents (NADES). Herschel-Bulkley equation

Ionic liquids


IL/NADES

τ0 (mPa)

ηo (mPa sn)

n

References

ethyl‑methylimidazolium ethylsulfate + 20 wt% Fe2O3 ethyl‑methylimidazolium ethylsulfate + 30 wt% Fe2O3 ethyl‑methylimidazolium ethylsulfate + 35 wt% Fe2O3 ethyl‑methylimidazolium ethylsulfate + 40 wt% Fe2O3 choline chloride + phenylacetic acid based @ 1:2 – 35 °C choline chloride + phenylacetic acid based @ 1:2 - 55 °C choline chloride + phenylacetic acid based @ 1:2 - 75 °C choline chloride + phenylacetic acid based @ 1:2 - 90 °C choline chloride + phenylacetic acid based @ 1:3 - 35 °C choline chloride + phenylacetic acid based @ 1:3 - 55 °C choline chloride + phenylacetic acid based @ 1:3 - 75 °C choline chloride + phenylacetic acid based @ 1:3 - 90 °C choline chloride + phenylacetic acid based @ 1:4 - 55 °C choline chloride + phenylacetic acid based @ 1:4- 75 °C choline chloride + phenylacetic acid based @ 1:4 - 90 °C

425.0 2300.0 3320.0 5610.0 16.3 14.2 24.5 9.4 551.0 370.0 9.0 2.8 37.9 4.3 5.1

58.0 74.0 76.0 105.0 205.6 74.1 35.3 23.8 187.1 59.9 25.6 21.7 340.9 19.2 13.1

1.0017 0.9956 0.9936 0.9757 0.945 0.958 0.977 1 0.826 0.977 1 1 0.888 1 1

[48]

The change of the yield stress values as a function of temperature is similar to the to the viscosity data [18] (Table 11). 5. Conclusion This review summarizes the various rheological behaviors of different combinations of imidazolium based ILs and NADES that are mainly based on choline chloride ILs. The shear flow and viscoelasticity characterizations were thoroughly investigated for the use in several flow dependent applications. NADES have been less elaborated from rheological perspective in comparison with ILs and it can be explained by their late development as sustainable and environmentally benign organic solvents. From the discussed results, literature clearly indicates that both ILs and NADES rheological properties are tuned by changing the nature of the benefactor (i.e. the cationic functional group in ILs and HBD for NADES). Pure imidazolium ILs and NADES showed diverse behaviors under the

[70]

effect of shear rate from Newtonian to non-Newtonian fluids. Moreover, the apparent viscosity of NADES has shown to be higher than that of ILs, where NADES ranged from as low as 0.05 Pa·s to as high as 2000 Pa·s at ambient conditions over an incremented domain of applied shear, while ILs ranged from approximately 0.02 Pa·s to 7 Pa·s. Moreover, it was also concluded that the addition of a solute or flow additives such as polymers, nanoparticles, nanofluids and water can significantly change the flow regime in the case of ILs. On the other hand, the temperature dependency of both solvent families agrees with the direct proportionality analogy with viscosity as a function of shear rate. Although the viscoelastic properties are essential to determine the stability and destruction of formed networks upon characterization of the synthesized solvents, yet a lack of oscillatory measurements were found. Several rheological models were collected featuring a set of analyzed data from several research papers that validate the consistency of the measured apparent viscosity against shear and temperature.

Table 11 Bingham model parameters for different Natural Deep Eutectic Solvents (NADES). Bingham equation

Deep Eutectic Solvents

IL/NADES

τB (mPa)

ηB (mPa·s)

References

choline chloride + phenylacetic acid based @ 1:2 - 35 °C choline chloride + phenylacetic acid based @ 1:2 - 55 °C choline chloride + phenylacetic acid based @ 1:2 - 75 °C choline chloride + phenylacetic acid based @ 1:2 - 90 °C choline chloride + phenylacetic acid based @ 1:3 - 35 °C choline chloride + phenylacetic acid based @ 1:3 - 55 °C choline chloride + phenylacetic acid based @ 1:3 - 75 °C choline chloride + phenylacetic acid based @ 1:3 - 90 °C choline chloride + phenylacetic acid based @ 1:4 - 55 °C choline chloride + phenylacetic acid based @ 1:4- 75 °C choline chloride + phenylacetic acid based @ 1:4 - 90 °C choline chloride + lactic acid @ 25 °C choline chloride + lactic acid @ 45 °C choline chloride + lactic acid @ 65 °C choline chloride + lactic acid @ 85 °C choline chloride + malic acid @ 25 °C choline chloride + malic acid @ 45 °C choline chloride + malic acid @ 65 °C choline chloride + malic acid @ 85 °C choline chloride + citric acid @ 25 °C choline chloride + citric acid @ 45 °C choline chloride + citric acid @ 65 °C choline chloride + citric acid @ 85 °C choline chloride + fructose @ 25 °C choline chloride + fructose @ 45 °C choline chloride + fructose @ 65 °C choline chloride + fructose @ 85 °C

9.937 16.8 6.7 0.9 712.4 35 14.9 9.1 31.2 6.1 1.4 271.41 228.13 155.8 207.38 958,109 84,657 4484.7 174.73 968,834 948,834 124,813 35,866 3029.6 862.77 607.42 663.41

203.6 73.6 38.3 25.2 160.4 60.7 24.5 24.4 35.3 18.0 13.0 396.7 153.1 78.0 36.6 27,492.0 9100.7 2509.0 797.1 834,114.0 41,657.0 10,298.0 3489.4 482.1 239.2 100.1 38.9

[70]

[18]


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