Preparation of fluoropolymer materials with different porous morphologies by an emulsion template method using supercritical carbon dioxide as a medium

Abstract

The choice of a suitable surfactant is key to the formation of a stable water-in-CO₂ (W/C) or CO₂-in-water (C/W) emulsion. It is even more critical in stabilization of the emulsion containing carbon dioxide (CO₂). In this study, the successful preparation of W/C emulsion was achieved by using the amphiphilic block polymer poly(ethylene glycol) methyl ether-b-poly(trifluoroethyl methacrylate) (mPEG₄₅-b-(TFEMA)_n) as a surfactant, in which CO₂ was used as a solvent for the fluoromonomer, trifluoroethyl methacrylate (TFEMA). In the case of the W/C emulsion, CO₂ and TFEMA were used as the continuous phase and water as the internal phase of the emulsion system. It has been found that in the length of the block polymer mPEG₄₅-b-(TFEMA)_n, the fluorine-containing chain end has a significant effect on the morphology of the polymer and the type of emulsion formed. The morphology of the polymer was observed by scanning electron microscopy which confirmed the type of emulsion formed. With the fluorine-containing end segment, the morphology of the polymer changes from a small hollow sphere in a large hollow sphere to a hollow spherical to a porous structure. Correspondingly, it could be concluded that the type of emulsion could go through the process from water-in-CO₂-in-water-in-CO₂ (W/C/W/C) emulsion to water-in-CO₂-in-water (W/C/W) emulsion to water-in-CO₂ (W/C) emulsion. Also, suitable co-surfactants were identified in this study. Investigations were also attempted to check the effect of the amount of surfactant, cross-linker and water/CO₂ ratio on the type of emulsion formed as well as the morphology of the resultant polymer.