Proton conduction mechanisms in GPTMS/TEOS-derived organic/silica hybrid films prepared by sol-gel process

Abstract

In this work, we employed impedance spectroscopy measurements to investigate the electrical properties of hybrid films obtained with the sol-gel process using 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethylorthosilicate (TEOS) at different GPTMS/TEOS molar ratios and temperatures of thermal treatment. For the GPTMS/TEOS-derived samples with 1:1 composition, the DC conductivity (σdc) and charge carrier mobility (μdc) increased linearly with heat treatment temperature from 25 to 80 °C, while σdc increased from 3.2 to 22.4 nS/cm with a 7-fold increase in the GPTMS concentration. These results could be rationalized with the Miller-Abraham model using a charge carrier activation energy of 0.54 ± 0.03 eV. Using FTIR spectroscopy we demonstrated that the structural arrangement of the hybrid matrix involves epoxy ring opening, thus favoring proton conduction, which occurs as in the Grotthuss mechanism via hopping between nearest oxygen atoms of polymerized glycidoxypropyl groups. It is significant that electrical properties of organic/silica matrices can be predicted and tuned for tailored applications using the modeling presented here.