Preparation of Surface-Porous PS Films with a Submicron-Scale Pore Size from a PS/PEG–THF Ternary Mixture Based on Ultrasonic Dispersion

A ternary polymer-solvent mixture has already been proposed to prepare surface porous films. However, the uncertainty of the formation mechanism of surface porous films and the multitude of influencing factors with unclear priorities lead to the failure to promote this method. Here, a surface-porous polystyrene (PS) film with a pore size of 0.6 μm was successfully prepared from a ternary PS/poly(ethylene glycol)-tetrahydrofuran (PEG-THF) mixture, using ultrasonic dissolution to provide a dispersion effect. The total polymer concentration, PEG molecular weight, PS/PEG mass ratio, dissolution temperature, and evaporation temperature can help to optimize surface porous structures. Based on the rheological behavior of the ternary PS/PEG-THF mixture and comparative experiments with the traditional dissolution method, the formation mechanism of surface porous structures has been revealed. After dissolution, the ternary mixture should be viewed as a two-phase dispersion, emphasizing the dispersion effect of the dissolution process. The formation of surface pores is derived from the transportation, arrangement, and evaporation of dispersed PEG-THF domains. Thus, the preparation of high-quality surface porous films through a ternary polymer dispersion mainly requires attention to two points: the dissolution and dispersion method and the solvent selection. To obtain submicron surface porous films, a synergistic effect of the two is required.