Structure, dielectric, thermal and I-V studies of electron beam irradiated PVDF-HFP/ LiClO4 electrolyte film L. Yesappa, M. Niranjana, S. P. Ashokkumar, H. Vijeth, M. Basappa, S. Ganesh, and H. Devendrappa
Citation: AIP Conference Proceedings 1953, 050059 (2018); doi: 10.1063/1.5032714 View online: https://doi.org/10.1063/1.5032714 View Table of Contents: http://aip.scitation.org/toc/apc/1953/1 Published by the American Institute of Physics
Structure, Dielectric, Thermal and I-V Studies of Electron Beam Irradiated PVDF-HFP/LiClO4 electrolyte film L Yesappa, M Niranjana, SP Ashokkumar, H Vijeth, M Basappa, S Ganesh, H Devendrappa * Department of Physics, Mangalore University, Mangalagangothri -574199, India *Corresponding author:
[email protected] Abstract. The effect of electron beam (EB) irradiation on polymer electrolyte (PVDF-HFP: LiClO4=90:10, PHL10) films prepared by solution casting method. FT-IR confirms the complexation between salt and polymer upon EB dose. Degradation of polymer and decrease in % of crystallinity from 50.10 to 40.96 at 2θ=19.90 o at 120 kGy dose indicates increased amorphousity confirmed by XRD. The TGA result show decrease in Tm from 460 oC to 418 oC is leads to degradation of polymer chain at higher dosage. The dielectric parameters have been determined and observed decreasing trend with increased frequency as well as temperature due to increase the mobility of charge carrier confirms the capacitive nature. I-V plots exhibit an ohmic behavior with applied voltage and irradiation dose. The results notice the change in polymer properties upon irradiation.
INTRODUCTION The different polymer electrolytes have different effects of radiation depending on their chemistry and physical properties. The EB irradiation is well controlling method to tailor the required physical properties of the polymeric materials by forming intermolecular bonds, degradation of polymer chain upon interaction. The study of structural and thermal behavior helps to understand the structural arrangement after expose to high energy [1]. The polymers undergo physiochemical changes such as production of free radicals and chain scission or cross-linking when exposed to radiation and it is important to understand the charge transportation mechanism in the polymers under applied field after significant changes by EB irradiation [2]. The process can effectively improve performance of many copolymers and it can able to change the structure properties of the copolymers by breaking the bonds with low crystallinity can improve the conductivity after exposing to radiation has paid more attention and offers new specific applications like LED’s, super capacitor, medical radiation therapy, and food processing [3]. The dielectric parameters are more complex due to competition between intra–inter chain process in the transport mechanism and radiation modification being still complex in polymer electrolytes. Presently, studied the EB effect on the physical properties and dielectric parameters including I-V characteristics of the PHL10 electrolyte films.
EXPERIMENTAL METHODS The polymer electrolyte films (PVDF-HFP:LiClO4=90:10, PHL10) was prepared by solution casting method using dimethylformamide (DMF) as a solvent and the was irradiated using 8.1 MeV EB energy at 40, 80 and 120 kGy dosage to investigated the structure, thermal, dielectric and I-V studies before and after EB irradiation.
2nd International Conference on Condensed Matter and Applied Physics (ICC 2017) AIP Conf. Proc. 1953, 050059-1–050059-4; https://doi.org/10.1063/1.5032714 Published by AIP Publishing. 978-0-7354-1648-2/$30.00
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RESULTS AND DISCUSSION FT-IR Spectroscopy and X-ray diffraction FT-IR results before and after EB irradiated PHL10 electrolyte film was shown in Figure 1(a). The peak at 1644 cm-1 of unirradiated film has shifted to 1654 cm-1 is assigned to stretching of C=O group is due chain scission over crosslinking and 1396 cm-1 with increase peak intensity shifts to 1391 cm-1 is assigned to -CH2- group stretching and the breaking of the carbonyl group confirms polymer degradation due to chain scission upon high EB dose [4]. The band appeared at 3558 cm-1 is attributed to the O–H stretching of the hydroxyl group in unirradiated film is shift to 3553 cm-1 indicates the modification in O–H group after 120kGy dose. These changes confirm the irradiation effect on the polymer chain. (a)
120kGy 1644
300 (b) 250 200 150 100 50 1200
3533
1391
900
80kGy
Intensity
T%
Unirradiated
1396 -CH2-
500
1000
1500 2000 2500 3000 -1 Wavenumber (cm )
80kGy
600
40kGy
1654 C=O
120kGy
3558 O-H
3500
4000
300 600 500 400 300 200 100 300 250 200 150 100 50
40kGy
(110) Unirradiated (111)
10
20
30
40
50
2 (Degree)
60
70
80
FIGURE 1. (a) FT-IR spectra and (b) X-ray diffraction patterns of PHL10 electrolyte before and after EB irradiation.
When PHL10 electrolyte is exposed to high energy, the well-defined peaks intensity decreases as shown in Figure 1(b). XRD pattern shows broad peaks at 2θ = 19.90 o (110) and 38.30o (111) signify the amorphous and crystalline peak of the unirradiated film and peak further broaden upon irradiation is confirms the decrease in crystallite size and shifts to 38.90o at 120 kGy dose is indicates amorphousity of the electrolyte film increases by decreasing degree of crystallinity [5]. The percentage of crystallinity decreases from 50.10 to 40.96 at 2θ=19.90 o upon 120 kGy dose and % crystallinity calculated using Χc=(Ac/Ac+Aa), where Ac, Aa are the area under the crystalline and amorphous peaks. The results confirm that the degradation of the polymer chain at higher dosage and correlates with FT-IR results.
Thermal Analysis The TGA/DTA thermogram of unirradiated and irradiated films reveals the one step degradation in the range of 420–480 °C as shown in Figure 2 is attributed to the degradation of polymer backbone and an endothermic process in DTA curve is associated with the melting temperature of crystalline phase of the host polymer. The loss of water content around 100 °C is suggests first degradation step of carbon–hydrogen scission occurrence and second stage in the range 110–305 °C is loss of the dopant from polymer matrix and complex degradation process takes place at 319 o C and 291 oC in DTA curves is corresponding to degradation of PHL10 electrolyte unirradiated and 120 kGy EB dose respectively. The third major loss from 305 to 565 °C is attributed to the destruction of polymeric chain backbone with decrease in degradation temperature from 459 to 418 oC for unirradiated and 120 kGy EB dose respectively [6] is clearly notice the change in molecular structure as a result degradation of polymer matrix leading to increase amorphousity [2]. It is observed that the initial decomposition temperature of the thermogram for the irradiated films reveal the melting temperatures (T m) gradually decrease and it shift towards lower temperature with increasing irradiation dose is confirms the enhancement in thermal stability; it may decrease the molecular weight of polymer electrolyte as a result creation of free radical or fragmentation leading to increase amorphousity at high EB irradiation dose [7]. XRD results are well supports to these results.
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70 o
TGA Curve DTA Curve
40
0.6
o
319 C
30
0.3
20 10
300
400
500 o
600
0.8
TGA Curve DTA Curve
50 40
0.6
o
291 C
0.4
30
0.2
10
0.0 200
60
20
0.0
0
0 100
418 C
285 C
70
1.0
o
o
Deriv. Weight (%/°C)
0.9
Deriv. Weight (%/°C)
Weight loss (mg)
1.2
305 C
50
120 kGy
80 o
459 C
60
90
1.5
Unirradiated
Weight loss (mg)
80
100
700
200
300
400
500
600
700
o
Temperature ( C)
Temperature ( C)
FIGURE 2. TGA/DTA curves of unirradiated and 120 kGy EB dose irradiated PHL10 electrolyte films.
Dielectric Studies The dielectric constant (ε') and loss (ε'') for unirradiated and 120 kGy dose irradiated PHL10 electrolyte films as a function of frequency at different temperatures are shown in Figure 3 and observed that dielectric parameters (ε' & ε'') decreases with increasing frequency because the polarization not follows the orientation direction at applied field. The ε' & ε'' increases with temperature for unirradiated and 120 kGy irradiated electrolyte films due to increase in charge carrier density at high temperature. 5
303K 313K 323K 333K 343K 353K 363K 373K 383K 393K
Unirradiated
5
5x10
5
5x10
5
4x10 5
''
4x10
5
3x10
5
2x10
'
5
3x10
5
1x10 5
3
7.70x10
3
6.60x10
3
5.50x10
3
4.40x10
3
3.30x10
3
2.20x10
3
1.10x10
3
303K 313K 323K 333K 343K 353K 363K 373K 383K 393K
120kGy
5
1.2x10
5
1.0x10
4
8.0x10
4
6.0x10
4
4.0x10
4
0
2x10
8.80x10
'
6x10
''
5
6x10
1
2
3
4
5
5
1x10
0
2.0x10
0.0 1
2
3
4
5
0.00 1
2
3
4
5
logf (Hz)
1
2
3
logf (Hz)
4
5
FIGURE 3. Variation of dielectric constant and loss (inserted) with frequency at different temperatures for unirradiated and 120 kGy EB dose irradiated PHL10 polymer electrolyte films.
The increasing trend of ε' & ε'' at different temperatures is attributed to formation of defects or disorders in the band gaps by chain scission and increase charge carrier density due to increase in the dissociation of ion aggregation in the polymer upon irradiation and therefore it confirm the EB irradiation effect [4]. The ε' is decreases with increased EB irradiation dose at high temperature as shown in Figure 4(a) is due to cross linking of free radicals stops the orientation of ions with applied field and reduction in free radicals after irradiation, detrapping of irradiated charge carriers in the defect sites and also bound charges cannot be polarize at higher EB dose. This process manifests in the form of dielectric loss because the induced charges gradually fail to follow reversing the field causing a reduction in the electronic oscillations at high temperature as well as high EB dose is attributed to the dilution effect of amorphous phase due to rearrangement of atoms and redistribution of primary defects by radiation influence [8]. The decreasing Tm is well correlates with these results.
I-V Characteristics The current increases gradually with applied voltage and EB dose as shown in Figure 4(b). The conduction mechanism in the polymeric materials reveals a linear nature and I-V plot exhibits an ohmic behavior; it means the
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current varies linearly with voltage [9]. The increased conductivity is due to the presence of conjugated and trapped ions in polymer chain and is attributed to the increase in number of charge defects in the polymer chain by chain scissioning process upon irradiation. 5
7x10
-5
(a)
5
6x10
5
-5
6.1x10
Current (A)
5x10
5
'
6.2x10
303K 313K 333K 393K
4x10
5
3x10
PVDF HFP PHL Unirr PHL 40kGy PHL 80kGy PHL 120kGy
(b)
-5
6.0x10
-5
5.9x10
5
2x10
5
1x10
-5
5.8x10
0 0
20
40
60
80
100
120
EB Dose (kGy)
0.04 0.06 0.08 0.10 0.12 0.14 0.16
Voltage (V)
FIGURE 4. (a) Variation of dielectric constant with EB dose and (b) I-V curves of PVDF HFP before and after EB irradiated PHL10 electrolyte films.
CONCLUSION The effect of irradiation in on electrolyte films have been confirmed by change in the carbonyl bands and also increases the amorphousity by decreasing the % crystallinity upon the EB dose. The dielectric parameters (ε' & ε'') decreases suddenly with increasing frequency and increases with temperature for unirradiated and 120 kGy irradiated electrolyte films is may be increase in charge carrier density and the ε' decrease with increased irradiation dose due to cross linking of free radicals stops the orientation of ions with applied field at high EB dose. These results suggest that, there is a possibility of improving polymer electrolytes properties on EB irradiation.
ACKNOWLEDGEMENTS Author thanks to the DAE-BRNS, Mumbai for sanctioned the project and also thank to PURSE, Mangalore University for TG/DTA facility.
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