Effects of Acid Modified SiO₂ on Ionic Conductivity and Blend Properties of LiBF₄ Doped PMMA/ENR 50 Electrolytes

Abstract

Previously, it was found that the addition of SiO2 filler can improve the homogeneity and enhance the ionic conductivity of lithium tetrafluoroborate (LiBF4) doped polymethyl methacrylate/50 % epoxidized natural rubber (PMMA/ENR 50) blend from 6.21 x 10-7 Scm-1 to 5.26 x 10-6 Scm-1. Unfortunately, this SiO2 filler tend to agglomerates thus obstructing the smoothness in the transportation of lithium ion in the polymer blend matrix. This unruly phenomenon was due to the formation of hydrogen bonding between the oxygen atom of SiO2 and the hydrogen atom from the moisture. Therefore, in this study, this SiO2 filler was modified using hydrochloric acid (HCl) to reduce the formation of hydrogen bonding between SiO2 and moisture. It was found that the modification was able to reduce the hydrogen bond in SiO2 filler. The CHNS analysis shows that the percentage of hydrogen reduces as concentration of acid increased. This was further confirmed from the FT-IR analysis in which the peak corresponding to Si-OH was reduces meanwhile the peaks corresponding to Si-O-Si increases as HCl concentration increased. As a result, the homogeneity of the blends was further improved. However, the ionic conductivity of the system was found slightly reduce by few magnitudes. Temperature dependence ionic conductivity of LiBF4 doped PMMA/ENR 50 filled HCl-SiO2 electrolytes shows nonlinear trend indicates that the system not obeys Arrhenius equation.