Ionic Conductivity in Gelatin-Based Hybrid Solid Electrolytes: The Non-trivial Role of Nanoclay

Abstract

In this study, the ionic conductivity behavior in hybrid gelatin-based transparent electrolytes including various types of nanoclays with different size, shape and surface properties was characterized. The effects of nanoclay type and nanoclay concentration as well as different experimental conditions, e.g., pH, temperature and crosslinking were also investigated. In general, the impedance spectroscopy results suggested a non-trivial role for nanoclay. Regardless of the nanoclay type, the ionic conductivity slightly increased first and then decreased by increasing the nanoclay concentration. Furthermore, among sodium montmorillonite (Na+MMT), lithium montmorillonite (Li+MMT), laponite and hydrotalcite, the hybrid electrolytes prepared by Li+MMT showed higher ionic conductivity. The results also showed that the chemical crosslinking along with sample preparation at optimum pH, where the gelatin chains might be efficiently adsorbed on exfoliated, negatively charged clay nanosheets, plays an important role. In comparison with the ionic conductivity of the neat sample at room temperature (∼10−7 S cm−1), a ten-fold increase was observed for the crosslinked sample containing 2 wt% of Li+MMT prepared at optimum pH 3.5. The conductivity behavior as a function of temperature revealed the obedience with the Vogel–Fulcher–Tammann (VFT) model for all samples, suggesting the important role of segmental motions in the ionic conductivity. Finally, a qualitative explanation was presented for the mechanism of the ionic conduction in gelatin-nanoclay hybrid electrolytes.