(722l) Preparation of a Fine Porous Thin Film by Phase Separation Induced in the Course of Drying An Immiscible Polymer Blend Solution

A polymeric porous structure was prepared by drying polystyrene (PS), polyethylene glycol (PEG), and solvent. The effect of drying rate and phase separation on the controllability of the pore size and number density of pores in the film was investigated by six different solvents: toluene, chlorobenzene, tetrahydrofuran (THF), methyl ethyl ketone (MEK), 1,4-dioxane, and chloroform. The pore size and density drastically changed with the different solvents and drying conditions. The polymer concentration at the onset of phase separation into PEG-rich and PS-rich phases also strongly affected the cellular structure. The solubility of PEG into the PS and the solvent solutions changed the concentration, which corresponds to the viscosity of PS-rich solution at the onset of the phase separation. The higher solubility of PEG in the solutions delayed the onset of phase separation during drying and increased the viscosity. The higher viscosity and the higher drying rate prevented the phase-separated PEG-domains from coalescing, and made the resulting porous size smaller and the pore density larger. The finest porous structure, whose pore size was c.a. 1 µm and whose pore density was 0.08 µm^-2, was prepared from PS/PEG and 90 wt% chloroform solution.