Effect of LiClO₄ Concentration on Structural, morphological and Thermal Properties of PMMA and PEO Polymer Blends

M. Jaipal Reddy^1*, M. Ravindar Reddy², A. R. Subrahmanyam², M. Maheshwar Reddy³,

A. Samba Siva Raor²

¹Department of Physics, Palamuru University, Mahaboob nagar-509101, Telangana., India

²Department of Sciences & Humanities, MVSR Engineering College,

Nadergul, Hyderabad - 501510, Telangana, India

³Department of Scince & Humanities, Sreenidhi Institute of Science & Technology,

Yamnampet, Ghatkesar, R. R. (Dist.)-501301, Telangana, India

*Corresponding Author E-mail: mjaipalreddy@gmail.com

ABSTRACT:

Structural, morphological and thermal Properties of PMMA-PEO-LiClO₄ solid polymer electrolyte blend films have been studied. PMMA-PEO-LiClO₄ solid polymer electrolyte blend films were prepared using solution casting technique. The blend films were characterized by X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM) and Differential scanning calorimetry (DSC). From XRD analysisit is observed that semi crystalline nature of pure PMMA shows that increase in amorphous nature with increasing concentrations of LiClO₄and PEO to PMMA blend.SEM images suggest that the surface morphology changes severely when LiClO₄ and PEO/ PMMA blend polymers, which shows the development of surface morphology from rough to smooth with increasing concentrationof LiClO₄ to PMMA/PEO. The smooth morphology is closely related to the interaction/ interface between the polymers PMMA/ PEO and Li ions due to cross – linking. Melting temperatures (T_m) of polymer electrolyte films were determined by DSC data.

KEYWORDS:PMMA, PEO, LiClO₄, XRD, SEM, DSC.

1. INTRODUCTION:

Solid Polymer Electrolytes (SPE) has attracted attention since more than four decades due to their practical applications [1-6]. SPE offers many advantages, such as high durability, high flexibility and low reactivity towards the electrodes. These eliminate the problems of corrosive solvent leakage and harmful gas for above ambient temperature operations and reduce packaging cost as well as improve self–life of the lithium metal electrodes [7–8].

In literature, researchers have worked on many host polymers e.g. poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC) and poly(vinyl acetate) (PVA) etc., to optimize electrical conductivity and other properties for their practical application as polymer electrolytes [8]. “Blending” of polymers is one of cheap and easy techniques used nowadays for the preparation of polymer electrolytes, compared to synthesizing a new polymer; wherein, the polymers are mixed physically and the final blend electrolyte thus obtained consists of the desired properties of each of the host polymers and possesses enhanced conductivity and improved properties [9-11]. Linear poly(methyl methacrylate) (PMMA) can form stable blends with linear poly(ethylene oxide) (PEO) due to van der Waals type bonding between the PMMA chains and the planar PEO segments [12– 15]. To increase ionic conductivity and thermal stability of polymer blends, LiClO₄ salt added to PMMA and PEO polymers. In the present work, solid polymer electrolyte blend films consisting of PMMA, PEO and LiClO₄ are examined for various concentration of wt%. The prepared polymer blend electrolyte films are characterized by XRD, SEM and DSC for the structural and thermal properties.

2. EXPERIMENTAL:

All the films were prepared by solution casting technique [16-18]. The polymers Poly(methyl methacrylate) (PMMA) (M.W~15000), poly(ethylene oxide) PEO (M. W. 2× 10⁵) and LiClO₄ salt were purchased from Sigma Aldrich. PMMA, PEO and LiClO₄ were separately dissolved in Tetra Hydro Furan (THF) and stirred by using a magnetic stirrer for 24-36 hours at room temperature. Later obtained homogeneous solution was poured in a glass Petri dish and kept at room temperature for several days to obtain dried blend films. The obtained films was visually examined for its dryness and free standing nature [19]. The thicknesses of dried polymer electrolyte blend films are around 1mm.

Table 1. Compositions of PMMA/PEO/LiClO₄blends films.

Sample code	wt.%
Sample code	PMMA	PEO	LiClO₄
A	100	0	0
B	95	5	5
C	90	10	10
D	85	15	15
E	80	20	20

The XRD patterns of the polymer films were recorded using an X-ray Diffractometer. The diffraction data were taken at room temperature with the Bragg’s angles 2θ from 10 to 70 degrees. SEM micrographs of pure PMMA and PMMA/ PEO/LiClO₄blend films were taken by using the scanning electron microscopy (SEM).The differential scanning calorimetry (DSC) of the different polymer electrolyte blend thin films were carried out using DSCQ20 instrument. About 4 to 5 mg of each sample was heated for the temperature range varying from 0⁰C to 350⁰C at a heating rate of 10⁰C.min^-1.

3. RESULTS AND DISCUSSIONS:

3.1 XRD

XRD pattern of pure PMMA and different concentrations of blend films of PMMA/ PEO/LiClO₄ are shown in Fig.1. In the case of Pure PMMA film, broad peak observed at 17⁰which indicates semi crystalline nature (Fig.1(A)). There are sharp peaks at 19.2⁰ and 23.4⁰in the pure PEO sample showed crystalline nature [20], which implies that pure PEO has a high degree of crystalline nature. A sharp crystalline peak observed at 21⁰ which is evident complete crystalline nature of LiClO₄[21]. When equal concentrations of PEO/LiClO₄ increasing progressively to PMMA, found that intensity of peaks decreases and also peaks are shifted towards higher Braggs angle, which indicates crystalline nature is decreasing with increase of concentration of LiClO₄ to PMMA/ PEO blend films. From the observations it is clear that the polymers undergo significant structural reorganization with the addition of LiClO₄ salt to PMMA/ PEO blend.

Fig.1 XRD pattern of pure PMMA and PMMA/PEO/LiClO₄ electrolyte blend films

3.2 SEM

Fig.2 shows the SEM images of pure PMMA and different concentrations LiClO₄ and PEO to PMMA. Appearance of rough surface in SEM micrograph of pure PEO was suggested several crystalline domains [22]. The SEM image (Fig. 2(A)) of PMMA shows rough surface and micro pore structure. When the concentrations of LiClO₄ to PMMA/PEO increases accordingly, surface of the films becomes rough to smooth, which indicates that smooth morphology is closely related to the interaction/ interface between the polymer electrolytes due to cross – linking.

3.3 DSC

Differential scanning calorimetry (DSC) is widely used to examine miscibility of polymer blends [23]. Fig.3 shows DSC thermogram (heat ﬂow vs. temperature) of the polymer blend electrolyte samples. The actual melting temperature (T_m) value of pure PMMA and PEO are 105˚C and 67˚C, respectively. The polymers PMMA and PEO films show a single T_m but when blend PMMA/ PEO with LiClO₄ salt found no such impression of melting temperature, it is that the crystalline nature of polymers is completely transformed into amorphous when LiClO₄ added to PEO/ PMMA blend. The DSC results corroborates with the results of XRD.

Fig.3 DSC curves of pure PMMA and PMMA/PEO/LiClO₄ electrolyte blend films

4. CONCLUSIONS:

Decrease of crystalline nature (i.e., increase of amorphous) of polymer electrolyte blend films of PMMA-PEO-LiClO₄ has been confirmed by XRD analysis. The SEM images suggest that the surface morphology changes severely when concentration of LiClO₄and PEO increases with equal wt.% to PMMA, which indicated the interaction/ interface between the polymers and Li ions salt due to cross – linking. Melting temperature (T_m) of polymer blend electrolyte films were found to be no change when concentration of LiClO₄and PEO increases to PMMA.

5. ACKNOWLEDGEMENT:

The authors would like to thank Head, BOS, Department of physics, Osmania University and JNTUH for their encouragement and one of the authors MRR thank to the Principal, Head (S&H), MVSR Engineering college for their constant support to carry out this work.

6. REFERENCES:

1. J. E. Bauerle, “Study of Solid Electrolyte Polarization by a Complex Admittance Method,” Journal of Physics and Chemistry of Solids, Vol. 30, No. 12, 1969, pp. 2657- 2670.

2. P. V. Wright, “Polymer Electrolytes—The Early Days,” Electrochimica Acta, Vol. 43, No. 10-11, 1998, pp. 1137- 1143.

3. V. D. Noto, S. Lavina, G. A. Giffin and E. Negro, “Polymer Electrolytes: Present, Past and Future,” Electrochimica Acta, Vol. 57, 2011, pp. 4-13.

4. J. Evans and C. A. Vincent, “Electrochemical Measurement of Transference Numbers in Polymer Electrolytes,” Polymer, Vol. 28, No. 13, 1987, pp. 2324-2328.

5. H. Block and A. M. North, “Dielectric Relaxation in Polymer Solutions,” Advances in Molecular Relaxation Processes, Vol. 1, No. 4, 1970, pp. 309-374.

6. Shazia Farheen and R. D. Mathad, International Journal of Advanced Science and Technology Vol.81 (2015), pp.49-52

7. M. R. Johan, O. O. Shy, S. Ibrahim, S. M. M. Yassin and T. Y. Hue, “Effects of Al2O3 Nano-Filler and EC Plasticizer on the Ionic Conductivity Enhancement of Solid PEO-LiCF3SO3 Solid Polymer Electrolyte,” Solid State Ionics, Vol. 196, No. 1, 2011, pp. 41-47.

8. Poonam Sharma, Dinesh Kumar Kanchan and Nirali Gondaliya, “Effect of Nano-Filler on Structural and Ionic Transport Properties of Plasticized Polymer Electrolyte”, Open Journal of Organic Polymer Materials, 2012, 2, pp. 38-44.

9. E.M. Abdelrazek, I.S. Elashmawi, and S. Labeeb, Chitosan filler effects on the experimental characterization, spectroscopic investigation and thermal studies of PVA/PVP blend films, Physica B, 405, 2010, 2021-2027.

10. L. Lee, S.J. Park, and S. Kim, Effect of nano-sized barium titanate addition on PEO/PVDF blend-based composite polymer electrolytes, Solid State Ionics, 234, 2013, 19-24.

11. Prajakta Joge, D.K. Kancha, Poonam Sharma and Nirali Gondaliya, IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861, PP 55-58.

12. Ito, H., Russell, T. P., Wignall, G. D. Interactions in Mixtures of Poly(ethylene oxide) and Poly(methyl methacrylate) Macromolecules 20 (9) 1987: pp. 2213 – 2220. http://dx.doi.org/10.1021/ma00175a028

13. Straka, J., Schmidt, P., Dybal, J., Schneider, B., Spevacek, J. Blends of Poly(ethylene oxide)/poly(methyl methacrylate). An i.r. and n.m.r. Study Polymer 36 (6) 1995: pp. 1147 – 1155. http://dx.doi.org/10.1016/0032-3861(95)93916-A

14. Lu, X., Weiss, R. A. Relationship between the Glass Transition Temperature and the Interaction Parameter of Miscible Binary Polymer Blends, Macromolecules 25 (12) 1992: pp. 3242 – 3246.

15. Yong LI, Qiuhua MA , Caiyi Huang, Guoqin Liu, ISSN 1392–1320 Materials Science (Medžiagotyra). Vol. 19, No. 2. 2013

16. M. Ulaganathan and S. Rajendran, J.Appl.Polym.Sci., 118 (2010) 646.

17. A. Manuel Stephen, N.G. Renganathan, T. Prem Kumar, R. Thirunakaran, S. Pitchumani and J. Shrisudershan, Solid State Ionics, 130 (2000) 123.

18. A. Manuel Stephen, T. Prem Kumar, N.G. Renganathan, S. Pitchumani, R. Thirunakaran, and N. Muniyandi, J.Power sources, 89 (2000) 80.

19. X. Helan Flora, M. Ulaganathan and S. Rajendran, Int. J. Electrochem. Sci., 7 (2012) 7451 – 7462.

20. YU Ying Hao, JIANG Peng, WANG FuRong, WANG Lefu and LI XueHui, Science China, 1608-1613 (2012).

21. X. Helan Flora, M. Ulaganathan, S. Rajendran, Int. J. Electrochem. Sci., Vol. 7 (2012) 7451 – 7462.

22. M. Jaipal Reddy, PP Chu, J. Siva Kumar, U V Subba Rao, J. Power Sources, 161 (2006) 535.

23. Shiao Wei Kuo and Feng Chih Chang, Macromolecules 2001, 34, 4089-4097.