Soft Materials
ISSN: 1539-445X (Print) 1539-4468 (Online) Journal homepage: https://www.tandfonline.com/loi/lsfm20
Preparation of stable dispersion of graphene using copolymers: dispersity and aromaticity analysis Sabih Qamar, Saima Yasin, Naveed Ramzan, Tanveer Iqbal & Majid Niaz Akhtar To cite this article: Sabih Qamar, Saima Yasin, Naveed Ramzan, Tanveer Iqbal & Majid Niaz Akhtar (2019): Preparation of stable dispersion of graphene using copolymers: dispersity and aromaticity analysis, Soft Materials, DOI: 10.1080/1539445X.2019.1583673 To link to this article: https://doi.org/10.1080/1539445X.2019.1583673
Published online: 01 Mar 2019.
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SOFT MATERIALS https://doi.org/10.1080/1539445X.2019.1583673
Preparation of stable dispersion of graphene using copolymers: dispersity and aromaticity analysis Sabih Qamara,b, Saima Yasinc, Naveed Ramzana, Tanveer Iqbalc, and Majid Niaz Akhtard a Department of Chemical Engineering, University of Engineering and Technology (UET), Lahore, Pakistan; bDepartment of Chemical Engineering, Muhammad Nawaz Sharif University of Engineering and Technology, MNSUET, Multan, Pakistan; cDepartment of Chemical Engineering, University of Engineering and Technology UET (KSK Campus), Lahore, Pakistan; dDepartment of Physics, Muhammad Nawaz Sharif University of Engineering and Technology, MNSUET, Multan, Pakistan
ABSTRACT
ARTICLE HISTORY
In this study, effectiveness of non-ionic block copolymers such as Lugalvan BNO12 and Triton X series (Triton X100 & Triton X405) has been reported for graphene dispersion in aqueous solutions. Stability of the aqueous graphene dispersions is investigated using UV–visible spectroscopy, Rheological, and Conductivity studies. Adsorption isotherms are constructed to determine the amount of polymers adsorbed on the surface of graphene by the spectroscopic analysis. Lugalvan BNO12 has been found to be adsorbed in higher amounts on the graphene surface compared to the Triton X series polymers. Thermogravimetric analysis (TGA) and Fourier Transform Infrared (FTIR) Spectroscopy investigations indicated grafting of polymers chains to the graphene surfaces. The dispersions prepared with optimum concentrations (as determined from adsorption isotherms) of polymers have shown lower viscosity and conductivity values. Lugalvan BNO12 has been found to be a better stabilizer for graphene than the Triton X series dispersants because the former contains two aromatic rings in its structure that acts as an anchoring group and helps in the stabilization of graphene dispersion in comparison to the single aromatic group in the Triton X series. The experimental results reported have shown that the aromaticity of polymeric dispersants plays significant role in the aqueous graphene dispersions. The non-ionic block copolymers that assisted dispersed graphene are potential candidates for the fabrication of various devices such as sensors, batteries, and supercapacitors applications.
Received 30 October 2018 Accepted 13 February 2019
Introduction Graphene, a comparatively new carbon material, has been used in many fields due to enormous and remarkable properties. Graphene is considered as an ideal candidate for various applications such as sensors, batteries, super capacitors, and H2 storage due to its atomically thin, 2D honeycomb structure (1). In dispersion-related applications, concentration, stability, and overall quality of dispersion remain extremely important. Recently, graphene has been actively investigated due to its versatile properties such as good thermal and electrical conductivity, large electron mobility, and high mechanical strength (2–6). Graphene has been applied in numerous applications (7–26), further it has been recently used for chemical adsorption, as a catalyst and as biological sensors. Number of challenges need to be addressed for graphene applications in which most important problem is poor colloidal stability in various solvents (27). Nanoparticles of graphene agglomerate in dispersions,
KEYWORDS
Graphene; polymeric dispersants; Fourier transform infrared spectroscopy; thermogravimetric analysis; adsorption isotherms; rheological measurements
which may decrease performance in applications. Hence, there is an interest by the researchers to introduce new and effective methods for the dispersion of graphene (28). It is desirable to modify the surface of graphene in order to control its characteristics. There are two types of modifications; first one is non-covalent modification which involves adsorption of molecules on the graphene surface, while second one is covalent modification which involves chemical reactions of graphene carbon atoms. Chemical modification involves severe chemical treatment which may alter graphene characteristics altogether (29,30). Recently, modification of graphene surface by liquid phase processing has been introduced as another effective method. But this method causes graphene aggregation due to strong van der waals forces among its sheets (8). The noncovalent modification of the graphene has resulted in higher enhancement of its characteristics as compared
CONTACT Sabih Qamar
[email protected] Department of Chemical Engineering, University of Engineering and Technology (UET), Lahore, Pakistan Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsfm. © 2019 Taylor & Francis Group, LLC
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to the covalent modification (31). This may be attributed to ease of availability of modifiers, simplicity of the chemical reaction, and retention of sp2 structure. In dispersions with non-ionic surfactants, hydrophilic part maintains the lamella in dispersed phase while hydrophobic part absorbs at the graphene surface. Therefore, non-covalent stabilizer must be used to alter the surface of graphene in aqueous or non-aqueous medium (32). Several stabilizers, certain polymers (29,30,33), surfactants (34,35), and aromatic molecules (36) prevent aggregation of graphene sheets. The capability to disperse unfunctionalized pristine graphene is significant for many applications like thin films, coating, polymer nanocomposites, functional fluids, and in environmental remediation. Certain solvents such as DMF (dimethylformamide) (37) or NMP (N-methyl-2-pyrrolidone) (23) were reported to disperse graphene but their high boiling points limit certain applications. Low boiling point solvents are most effective for stable dispersions of graphene. From this point of view, stable dispersion of pristine graphene in aqueous medium is important for graphene-based applications. Nano cellulose has been reported to stabilize the dispersion of rGO (38). Copolymer PVP-b-PEO has ability to disperse graphene in ethanolic and aqueous media. PVP-b-PEO block copolymer has been found to be a better stabilizer for dispersion of graphene than that of PS-b-PEO and P123 (28). Furthermore, the PEO-b-PVP-based graphene dispersions have been reported to be stable than that of the PEO-b-PS or PEO-b-PPy (39). Major interest has always been to prepare a stable dispersion of graphene for longer period by the assistance of polymers. Dispersions of graphitic carbon black particles have been examined using different polymeric ionic and non-ionic dispersants in aqueous and non-aqueous media. The study concluded that naphthol anchor group-based block copolymers are better surfactants than that of the PEO-PPO-PEO copolymer-based surfactants for graphitic carbon black dispersions (40–42). Here, we present the preparation of stable dispersion of graphene in aqueous medium with the help of three nonionic copolymers. Various microscopic and spectroscopic
Figure 1. Molecular structure of Triton X Series.
techniques were used to evaluate the stability of graphene dispersions in aqueous medium. Lugalvan BNO12, Triton X100, and Triton X405 were selected from a wide range of available dispersants. Triton X100 and Triton X405 have same anchor group having one aromatic ring but different PEO (Polyethylene oxide) stabilizing chain while Lugalvan BNO12 anchoring group has two aromatic rings. Thus, it is desirable to investigate the stable dispersion of graphene by the assistance of polymers in aqueous medium.
Materials and Methods Materials Lugalvan BNO12, Triton X405, and Triton X100 were used as dispersants. Graphene, nanoplatelets, grade C black in color having surface area 500 m2/g, was supplied by XG Sciences, Lansing, MI 48911, USA. Naphthol Ethoxylate (Lugalvan BNO12) was purchased from BASF, Ludwigshafen, Germany. Triton X100 and Triton X405 were provided by Sigma Aldrich, st Loius, MO 63178, USA. Common properties of these polymers are given in Table 1. Molecular structures of Lugalvan BNO12 and Triton X series dispersants are depicted in Figures 1 and 2, respectively. Adsorption Measurements Dispersions of graphene (0.15% by weight) were prepared at different concentrations of the polymeric dispersants (0 to 800 ppm for Lugalvan BNO12, 0 to 200 ppm for Table 1. Characteristics/properties of polymeric dispersants (40). Polymeric dispersants Lugalvan BNO12 Chemical formula C34H56O13
Triton X-100 (C14H22O(C2H4 O)10) Appearance Yellow liquid Viscous colorless liquid Density Approx. 1.06 g/mL at 1.13–1.15 g/cm3 25°C Melting point 6°C Boling point 270°C Molecular weight 672.809 g/mol 647 g mol−1 No of ethylene 12 10 oxide units Naphthol Yes No Alkyl phenyl No Yes (Octyl)
Triton X-405 (C14H22O(C2H4 O)40) Viscous paleyellow liquid 1.096 g/mL at 25°C −4°C 120°C 1968.47 g/mol 40 No Yes (Octyl)
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Figure 2. Molecular structure of Lugalvan BNO-12.
Triton X405 and 0 to 250 ppm for Triton X100) in water. These dispersions were ultrasonicated at 40 kHz for 1 h. The equilibrium concentration of resulting solutions was determined based on the separation from of the graphene particles and supernatant from the centrifugation of top layer of the ultrasonicated solution after 1 week. After centrifugation, some graphene particles were also seen to be present in the clear solution. Therefore, millex milipor syringe-driven micro filters (0.23 microns) were used to get clear solution. UV/VIS spectrophotometer (SHIMADZU Model UV-1800, Duisburg, Germany) was used to determine the remaining concentration of polymer in solution by determining the absorbance at 274 nm (40).
FTIR Analysis Samples for the Fourier transform infrared (FTIR) analyses were prepared as described in section of adsorption measurements at optimum concentration obtained from adsorption measurements. The dispersions were placed without any disturbance. After 7 days centrifugation of upper layer was done at 9,000 rpm for half hour, stabilized graphene sheets by block copolymers were collected, dried, and used for analysis as shown in Figure 3. FTIR analyses of the dried samples were performed on a Perkin Elmer L1600 FTIR spectrometer, Llantrisant, UK at room temperature.
TGA Analysis Thermogravimetric analysis (TGA) was used to determine the weight loss (degradation) with respect to
temperature for the dispersions. Same procedure was adopted for the sample preparation as depicted in section FTIR Analysis. TGA was performed on a SDTQ600 thermal analyzer, TA Instruments, New Castle, USA. TGA were performed with a heating rate of 10°C/ min from room temperature to 600°C in an inert (N2) atmosphere with a purge flow of gas at 20 cm3/min.
Rheological Measurements Aqueous dispersions of graphene (7–20 wt%) were prepared using known concentrations of three dispersants. Viscosity measurements were performed on a concentric cylinder geometry Rotary Rheometer of RHEOTEST Medingen model RN 5.1 OttendorfOkrilla Germany.
Conductivity Measurements The solution for the dispersions of graphene (1 wt%) was prepared to determine the electrical conductivity. The conductivity measurements were made using a conductivity measurement set Qcond 2200 from VWR International, Darmstadt, Germany. For electrical conductivity measurements, two types of dispersions were synthesized. One with dispersant and other without dispersant were prepared for the conductivity analysis. Solutions were prepared at optimum concentration that was obtained from adsorption isotherm.
Figure 3. Schematic diagram for graphene dispersion and stabilized graphene collection.
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Figure 4. Adsorption isotherm of graphene (0.15% by weight) using Lugalvan BNO12. Solid line is Langmuirian fit using best fitting values of K = 0.0127 m2/mg and Γm = 5.2 mg/m2.
Figure 5. Adsorption isotherm of graphene (0.15% by weight) using Triton X405 and Triton X100. Solid line is Langmuirian fit using best fitting values of K and Γm. ● Using Triton X405 (K = 0.0375 m2/mg and Γm = 4.3 mg/m2). ▲ Using Triton X100 (K = 0.0259 m2/mg and Γm = 3.9 mg/m2).
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Results and Discussion Adsorption Results Figures 4–5 show adsorption isotherms of the polymeric dispersants in aqueous dispersions for graphene. Figure 4 presents the adsorption isotherm of Lugalvan BNO12 block copolymer, while the adsorption isotherms of two Table 2. Maximum amount of polymer adsorbed from adsorption isotherms. Maximum amount adsorbedðmg=m2Þ ðΓmax Þ
Lugalvan BNO12
Triton X-100
Triton X-405
5.2
3.9
4.3
5
block copolymers Triton X100 and Triton X405 are shown in Figure 5. The optimum concentrations for three polymeric dispersants are determined to be: 5.2 mg/m2 for Lugalvan BNO12 (Fig. 4), 4.3 mg/m2 for Triton X405, and 3.9 mg/m2 for Triton X100 (Fig. 5) from respective adsorption isotherms. The adsorption isotherms are seen to be following the Langmuirian behavior. The amount of polymer adsorbed on the graphene based on the Langmuirian model (Equation 1) is presented in Table 2. Figures 6–7 show the linear form of Langmuir equation. Figure 6 shows the linear form of the equation for Lugalvan BNO12, while Figure 7 presents the linear forms of equation for other two block copolymers (Triton X100 and
Figure 6. Linearized plot of Langmuirian isotherm of Lugalvan BNO12 adsorbing onto Graphene (0.15% by weight).
Figure 7. Linearized plot of Langmuirian isotherm of Triton X405 and Triton X100 adsorbing onto graphene (0.15% by weight). ▲Triton X100, ∎Triton X405.
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Figure 8. FTIR Spectra of G, G-BNO12, G-X405, and G-X100.
Triton X405). Maximum amount of polymer adsorbed was obtained from the slope of these isotherms. Ce Ce 1 ¼ þ (1) KΓm Γ Γm The experimental results show that amount of polymer adsorbed on the surface of graphene was greater in case of Lugalvan BNO12 (5.2 mg/m2) as compared to Triton X-100 (3.9 mg/m2) and Triton X-405 (4.3 mg/m2) also shown in Table 2. Molecular structure of the dispersant plays a very important role in the graphene dispersions. In case of Lugalvan BNO12, higher adsorption can be attributed to the presence of naphthol having two aromatic rings in its anchoring chain. π–π interactions along with aromatic rings in the surfactants may have been responsible for the better adsorption in case of Lugalvan BNO12 as compared to Triton X-100 and Triton X-405 that have only one benzene ring in their anchor group. Similar results in dispersions of graphitic carbon black particles have also been reported in the literature using these three non-ionic dispersants in aqueous medium (40). Comparatively higher amount of the polymers were adsorbed in case of graphene in comparison to the graphitic carbon black particles for aqueous dispersions. Furthermore, the polymeric dispersants adsorbed on the graphene surface can also be controlled by the length of stabilizing chains as depicted from the adsorption isotherms. Triton X series contains an alkyl (octyl) phenol group that acts as an anchor group having only benzene ring. Both copolymers of Triton series have same anchor group but different size of stabilizing chains in their structure. Triton X405
contains 40 ethylene oxide groups whereas Triton X100 possesses 10 ethylene oxide groups, and therefore Triton X405 has been adsorbed in greater amount compared to that of the Triton X100. Similar results have been reported by other researchers for the adsorption of PE/F polymers onto various surfaces (43–45). Therefore, PEO (polyethylene oxide) chain plays an important role for the adsorption of polymers on the graphene surfaces along with anchoring group.
Fourier Transform Infrared (FTIR) Analysis FTIR spectra provided information regarding the molecular orientation of polymeric-based graphene structure. The spectra for Graphene-Lugalvan BNO12(G-BNO12), Graphene-Triton X405(G-X405), Graphene-Triton X100 (G-X100), and Graphene (G) were investigated to determine the confirmation of copolymers adsorbed on the surface of graphene. The FTIR spectra for the polymericcoated graphene indicate polymer grafting to the surfaces as shown in Figure 8. FTIR spectrum of G-BNO12, G-X405, and G-X100 clearly exhibit a C–H stretch at 2800–3000 cm−1 and carbonyl stretches at 1720–1740 cm−1. Meanwhile, at 1640–1680 cm−1, a characteristic double carbon–carbon aromatic bond (C=C) was observed. A single weak bond at 1360 cm−1 is recognized to carbon–hydrogen alkyl and another characteristic single bond at 1254 cm−1 is attributed to carbon– oxygen (C–OH); a carboxylic acid bond is observed for G-BNO12, G-X405, and G-X100. Figure 8 also revealed the vibrations of C–H bond at 610–700 cm−1. A peak at 3650–3850 cm−1 may indicate presence of lower
SOFT MATERIALS
concentration of copolymers in the surfactants. In short, curves exhibit characteristic peaks at 2840, 1730, 1640, and 1340 cm−1 corresponding to C–H, C=O, C=C, and C–OH vibrations representing the carbonyl and benzene carboxyl groups. Thermogravimetric (TGA) Analysis Thermal characteristic of graphene dispersions prepared by block copolymers was determined using a thermogravimetric analyser (TGA). The TGA curves of G, G-BNO12, G-X405, and G-X100 are presented in Figure 9. TGA curve for pure graphene (G) indicates a weight loss of only 19 wt%. The incipient degradation for pure graphene is observed to be at 300°C, whereas the polymer-coated graphene started decomposition at around 300–350°C. These differences may be attributed to deviation caused by thermal degradation of the block copolymers on the surface of graphene. Therefore, it can be inferred that the copolymers were adsorbed on the graphene surfaces. The adsorption, rheological, and conductivity measurements also confirmed the graphene coating by polymeric dispersants. Furthermore, the thermal degradation in all cases has been observed to take place in multiple steps. For example, G-BNO12 sample degraded only 8% at 375°C while 15% loss in weight has been observed in case of the G-X405 at a temperature of 425°C. Similarly, a 10% decrease in the weight of G-X100 has been seen at 300°C. In addition, maximum 60% loss in weight was observed up to 600°C which may be attributed to the thermal degradation of the dispersants. Since, X-405 contains higher
Figure 9. TGA curves of G, G-BNO12, G-X405, and G-X100.
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number of stabilizing ethylene oxide units (x = 40) in comparison to the X-100 (x = 10), more degradation has been observed for the X-100. Rheological Measurements Figure 10 shows how viscosities of graphene dispersions (10% by volume) vary with the change in shear rate at different concentrations of surfactant. It is clear from Figure 10 that higher values of viscosities were obtained at lower shear rates and vice versa. Further, the dispersions of graphene at the lower polymeric concentrations gave higher values of viscosities as compared to that of the dispersions at higher concentrations. This behavior can be attributed to the agglomeration of graphene particles at lower concentrations. Minimum viscosities were observed at the optimum polymeric concentration obtained from adsorption measurements. The viscosities of dispersions were observed to be constant at a shear rate of 600 s−1 as shown in Figure 10. Therefore, the shear rate of 600 s−1 has been selected for the rheological measurements. Figure 11 depicted a relationship between surface coverage of the graphene with Lugalvan BNO12 and ratio of dispersion viscosity to solvent viscosity called relative viscosity at constant high shear rate (600 s−1). Minimum viscosity was observed at the optimum concentration of all polymers determined from the adsorption isotherms. At concentration other than optimum concentrations, higher values of viscosities were observed for all dispersants. Figure 12 also shows a similar rheological behavior for the Triton X100 and the Triton X405 but higher
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Figure 10. The dependence of viscosity of graphene dispersions (volume fraction = 0.10) as a function of shear rate at different concentrations of surfactant (Lugalvan BNO12). Symbols are: ∎ The surface coverage is 4.0 mg/m2. ● The surface coverage is 4.3 mg/m2. ▼ The surface coverage is 4.6 mg/m2. ▲ The surface coverage is 4.8 mg/m2.
viscosity values as compared to Lugalvan BNO12. Analogous rheological results have been reported for the dispersions of graphitic carbon black particles using non-ionic dispersants in aqueous medium (40). Although the viscosity values reported by Yasin et al. (40) for the graphitic carbon black are higher than that of the present work for the graphene dispersions. This may be due to a comparatively higher reactivity between the graphene and the polymeric structure. Due to incomplete surface coverage of the particles at lower concentrations, higher viscosity values were observed based on the agglomeration of particles. The polymeric dispersant amounts at optimum concentrations obtained from rheological measurements and adsorption isotherms are listed in Table 3. The adsorption isotherms show slightly higher values of the adsorbed polymers than that obtained from the rheological measurements as depicted in Table 3. These observations can be validated from literature in the case of the suspensions viscosities at optimum concentrations (46,47). Figures 13–14 show variations of the relative viscosities based on the volume fraction of graphene at high and low shear rate, respectively. Further, an increase in the viscosity values was observed at higher volume fractions, but it increases more frequently at low shear rates.
Conductivity Measurements Table 4 shows electrical conductivity values of the aqueous dispersions of graphene with Lugalvan BNO12, Triton X405, Triton X100, and without surfactant. The samples without dispersants show higher electrical conductance as compared to that of the polymer-based graphene dispersion. The conductivity values of graphene dispersions were impeded after stabilization of graphene with copolymers. The relative conductivity values were found to be in the order: Lugalvan BNO12 < Triton X405 < Triton X100 < No Dispersant
This order may have originated due to the presence of polymer molecules on the graphene surface. The dispersions of block copolymers show lower relative conductivity than that of the aqueous dispersion without dispersant. Relative conductivity for Lugalvan BNO12-based dispersion was much lower than that of the blank samples and the Triton X405 and the Triton X100 dispersions. Moreover, Triton X100 shows higher conductivity among all three dispersants. Flocculation of graphene particles might have been the main reason for the higher
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Figure 11. High shear rate (600 s−1) viscosity of graphene (volume fraction = 0.10) dispersions as a function of the surface coverage using Lugalvan BNO12.
Figure 12. High shear rate (600 1/s) viscosity of graphene (volume fraction = 0.10) dispersions as a function of the surface coverage using Triton X100 and Triton X405. Symbols are: ▲ Graphene (volume fraction = 0.10) using Triton X100. ● Graphene (volume fraction = 0.10) using Triton X405.
values
of
the
electrical
conductance.
Lower
conductivity values of Lugalvan BNO12 may imply
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Table 3. Comparison of optimum concentration of polymers obtained from Adsorption isotherms and Rheology measurements of aqueous graphene dispersions. Polymer Optimum concentration from adsorption,Γ (mg/m2) Optimum concentration from Rheology, η (mg/m2)
Lugalvan BNO12
Triton X100 Triton X405
4.6
3.4
3.7
4.53
3.30
3.59
that the higher amount of polymer was adsorbed on the surface of graphene dispersed in water than other polymers. These observations are consistent with the UV–vis spectroscopy and Rheological measurements indicating higher affinity of Lugalvan BNO12 to the graphene particles. This may be due to the presence of naphthol as an anchor chain, whereas in case of the Triton series dispersants, anchor chain (alkyl phenyl) has been responsible for the adsorption. Hence, block copolymers play a vital role for the stabilization of the aqueous graphene dispersions, and a good stability can be obtained at optimum concentration. At concentrations higher and lower than optimum concentration, higher conductivity values were obtained because particles become flocculated. In other words, these polymeric dispersants provided enough steric barriers surrounding the graphene particles and produced
dispersions of good quality with lower relative conductivities. Carbon-based particles may be agglomerated due to the absence of surfactants, and higher values of viscosity and conductivity have been reported (48,49). Furthermore, higher values of electrical conductivity can be observed when particles agglomerate. In absence of these polymerbased dispersants for graphene dispersions, higher values of electrical conductivity and viscosity were measured. Stronger polymer adsorption on graphene surface provided lower values of conductivity and viscosity which show that dispersants anchor group and stabilizing layer gave better quality dispersions.
Conclusions Structure of polymeric dispersants plays major role in the adsorption of block copolymer dispersants on graphene surfaces. Lugalvan BNO12 adsorbs more on the graphene particles due to the presence of naphthol anchor group having two benzene rings in its structure as compared to other dispersants Triton X100 and Triton X405 which contain one benzene ring in alkyl phenyl anchor chain. The adsorption of polymers on graphene surfaces prevents agglomeration of graphene, and thus improves the quality and the stability of dispersions. Polymeric dispersants having benzene ring in their structure were proved as good stabilizer for
Figure 13. High shear rate (600 1/s) viscosity of graphene dispersions as a function of solid volume fractions in water. Symbols are: ∎ Lugalvan BNO12 (4.53 mg/m2). ▲ Triton X100 (3.30 mg/m2). ● Triton X405 (3.59 mg/m2).
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Figure 14. Low shear rate (1/s) viscosity of graphene dispersions as a function of solid volume fractions in water. Symbols are: ∎ Lugalvan BNO12 (4.53 mg/m2). ▲ Triton X100 (3.30 mg/m2). ● Triton X405 (3.59 mg/m2).
Table 4. Relative conductivity with and without polymeric dispersants in graphene dispersions. Dispersants Relative conductivity
No Dispersant 10
Lugalvan BNO12 1.2
Triton X405 2.5
Triton X100 3.2
aqueous graphene dispersions. FTIR and TGA investigations suggested that the polymer molecules have been grafted to the graphene surface. Dispersants effectiveness was proved from rheological measurements by providing lower values of viscosities at optimum concentration of dispersants. Lugalvan BNO12 showed lowest value of viscosities as compared to that of the other dispersants, and same consistency was observed for electrical conductivity. Therefore, the polymeric stabilized dispersions of graphene may be used for the fabrication of batteries, sensors, and super capacitors applications.
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