Self-Assembly of Nanofillers in Improving the Performance of Polymer Electrolyte Membrane

Understanding structure-property relationship between polymernanoparticle interface and the distribution of interfacial region and its properties is crucial in establishing the bulk properties of polymer like mechanical stability and conductivity. In this article we try to draw a comparison of the effect of silica nanoparticles modified with three different modifiers on the properties of oxypolybenzimidazole (OPBI) to understand the role played by the chemical structure of the organic modifying molecule. We highlight how small changes in the structure of the chosen molecule can bring about substantial improvements in polymer nanocomposites owing to the self-assembly of nanofillers. We use aminopropyltriethoxysilane (AMS), N-(3-trimethoxysilylpropyl) diethylenetriamine (LAMS) and ionic liquid modified silica (ILMS) for the surface modification of silica nanoparticles. The extent of interfacial interaction between each of these silica nanoparticles with OPBI matrix was found to be in the order OPBI/AMS < OPBI/LAMS < OPBI/ILMS. The increased interaction from AMS to LAMS to ILMS manifests as stronger adhesion between the polymer and the nanofiller particles that reflects in three important properties i.e storage modulus, acid doping level and proton conductivity of the nanocomposite membranes. Using TEM microscopy we demonstrate the distinct morphological changes induced by the self-assembly of differently modified silica nanoparticles and correlate the morphological features to the observed properties. This systematic study represents a significant step towards predicting desired/undesired nanocomposite properties.