The effect of choline chloride/1,4-butanol deep eutectic solven on the structural, morphological, thermal and electrical properties of PMMA-based electrolytes films / Nur Fadilla Abdul Khani

Previously, the brittleness of PMMA-based polymer electrolyte (PE) films has been successfully improved by the addition of ionic liquid (IL). However, ionic liquid is expensive, requires tedious preparation technique and has toxicity issue. Alternatively, deep eutectic solvent (DES) has been used as the replacement of IL as it is cheaper, highly biodegradable, less toxic and requires simpler synthesis processes. Thus, in this study, deep eutectic solvent (DES) namely Choline Chloride/1,4 Butanediol was incorporated into the PMMA-based PE via solution casting technique. Lithium triflate (LiTf) was also doped into the system to provide additional charge carrier. The effect of various amount of DES towards the structural, morphological, and electrical properties of PMMA-based PE films were determined using Fourier Transform Infrared Spectroscopy (FTIR), optical microscope (OM) and electrochemical impedance spectroscopy (EIS) respectively. Solid, flexible and free-standing film with improved ionic conductivity (4.5x10-6 S cm-1) was successfully obtained by adding 30% of DES into the PMMA/LiTf electrolytes. This was due to the bulky structure of DES, with the amount of 30%, has occupied the space between PMMA chains and hinders the formation of hydrogen bonding. This minimization of hydrogen bonding enables the lithium ion from the salt, LiTf to freely move and improves the ionic conductivity. This can be supported by OM analysis which showed the reduce number of grains related to the amorphousity of the sample. However, the addition 10% DES produced brittle film with drop in ionic conductivity. This is caused by the occurrence of ion multiples and ion aggregates which can be further supported by the increase in the grain number as observed from OM micrograph of PMMADES10. From the FTIR analyses, the interaction of LiTf and DES with the oxygen atoms (coordinating sites) of PMMA were observed.