Preparation and Proton Conductivity of Nanocomposite Membranes Based on Poly(Vinyl Alcohol)/Silica Nanoparticles Modified with Sulfonated Monomers

2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and styrene sulfonic acid sodium salt (SSA) as sulfonated monomers were grafted onto the brominated silica nanoparticle (BSN) via surface-initiated atom transfer radical polymerization (SI-ATRP) where CuBr/bipyridine was used as a catalyst/ligand system. Grafting amounts of the sulfonated polymers onto the BSN were estimated from thermogravimetry analysis curves to be 47.6% and 28.1% for PAMPS and PSSA, respectively. Polyvinyl alcohol (PVA)-based membrane containing pristine silica and silica nanoparticles grafted with sulfonated polymers were prepared via solution casting and then cross-linking in an acidic acetone solution containing glutaraldehyde. Prepared polymer electrolyte membranes (PEMs) were then characterized by ion exchange capacity (IEC), water uptake (WU) and proton conductivity. It was found that IEC, WU and proton conductivity of the PVA-based membranes increase by increasing the SN, especially sulfonated polymer-modified SN, loading up to 10 wt%. It was found that the higher the grafting percentage of sulfonated monomer onto SNs is, the higher the proton conductivity of the nanocomposite membrane will be. It was found that both hydrophilic nature and grafting efficiency of the sulfonated hydrophilic monomers can play important roles in proton conductivity of the PVA-based membranes.