Tailor-made fumed silica-based nano-composite polymer electrolytes consisting of BmImTFSI ionic liquid

Abstract

In this work, nano-sized fumed silica (SiO2) was embedded in poly(methyl methacrylate) (PMMA)–poly(vinyl chloride) (PVC) blend with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide) (BmImTFSI) as ionic liquid. These composite polymer electrolytes (CPEs) were prepared by solution casting technique. The samples followed Arrhenius behavior in the temperature-dependence of ionic conductivity and further proved the ionic hopping mechanism in the polymer electrolyte. It is suggested the formation of three-dimensional polymer network among the aggregates weakens the interaction of polar group of the polymer backbone and initiates the ionic decoupling process. The mobile ions from adjacent sites would occupy this vacant site and reform the interactive bond with the polymer backbone whereby the ionic hopping mechanism is generated. The activation energy (Ea) is further determined. The higher the ionic conductivity, the lower the activation energy. The maximum ionic conductivity of (8.26 ± 0.02) mScm−1 was achieved at 80 °C upon inclusion of 8 wt% of SiO2. X-ray diffraction (XRD) analysis revealed the higher amorphous region with increasing SiO2 mass loadings. The coherence length is further determined by using Debye–Scherrer equation. Higher amorphous region in the polymer matrix is conferred by showing the lower coherent length. Scanning electron microscopy (SEM) was applied to examine the morphology of polymer electrolytes. Based on the differential scanning calorimetry (DSC) study, glass transition temperature (Tg) and melting temperature (Tm) were decreased. Highly flexible polymer chain is produced when the Tg was lowered down. On the other hand, thermal stability of polymer electrolytes was increased by SiO2 dispersion, as depicted in thermogravimetric analysis (TGA).