Proton conductance and spectroscopic characteristics of acid-doped polymer gels based on poly(ethylene oxide)-modified polymethacrylate

Proton-conducting polymeric gels have been prepared by swelling a polymethacrylate-based polymer matrix in aqueous solutions of inorganic and organic acids such as sulfuric (H2SO4), hydrochloric (HCl), phosphoric (H3PO4), acetic (HAc), and succinic acids (HSc). The polymer matrix was composed of cross-linked poly(ethylene oxide)-modified polymethacrylate (PEO–PMA) with different plasticizing components of poly(ethylene glycol) dimethylether (PEGDE), dimethylformamide (DMF), and propylene carbonate (PC). The polymeric gels were characterized by conductometric and spectroscopic measurements. High ionic (proton) conductivity in the range of 6.4×10−4–4.2×10−2 S cm−1 were obtained at room temperature (22 °C), depending on the dopant acids, the type of plasticizers, and the polymer composition. The H3PO4- and HAc-doped films exhibited thermal stability in the temperature range of 20–80 °C. Possible proton transport mechanisms in the PEO–PMA-based gels were discussed based on the spectroscopic results of FT-IR, UV/VIS, X-ray diffraction (XRD), and fluorescence spectroscopy. The effects of water molecule absorbed in the polymer, together with the entrapped plasticizer (PEGDE, DMF, and PC), play important roles in obtaining the high ionic conductivity, through the reduction in the local viscosity of the gel films.