Colloid silica nanoparticles trapped morphology of polymer blends during solvent evaporation

Abstract During the solvent evaporation induced phase separation of PS and PMMA blends with silica nanoparticles, the dispersed and bicontinuous morphologies need to be stabilized by the absorption of silica nanoparticles at the interface. In order to accomplish this, the silica nanoparticles need to be chemically neutral to PS and PMMA homopolymers. For this purpose, their surfaces were modified by attaching mono-hydroxyl group terminated polystyrene poly(methyl methacrylate) random (PS-r-PMMA-OH) copolymer via the condensation reaction between the hydroxyl groups of silica particles and copolymer. The resulting morphology was found to be affected by the rate of solvent evaporation, blend compositions, particle loading and size. In the symmetric blend system, the dispersed phase was observed at low evaporation rate and bicontinuous morphology was obtained at high evaporation rate. The silica nanoparticles were found to be densely packed at the interface of PS and PMMA. For asymmetric blend system, only dispersed phase was observed at both low and high evaporation rates. The size of phase separated domains decreases with increasing solvent evaporation rate and particle loading. The silica nanoparticles with smaller size resulted in relatively smaller domain size due to their higher surface area to volume ratio. Porous membranes with partially exposed nanoparticles were fabricated by etching PMMA phase in acetic acid.