Ordered and foam structures of semifluorinated block copolymers in supercritical carbon dioxide

Abstract

This paper reports the appearance of a unique foam structure and pressure-induced order–order transition (OOT) of semifluorinated block copolymers in supercritical carbon dioxide (scCO₂). The morphological transition of block copolymers with the fluorinated block in scCO₂ is induced by the increasing apparent volume fraction of the fluorinated domain, which is preferentially swollen with CO₂. The poly(styrene-b-perfluorooctylethyl methacrylate) (PS-PFMA) and PS-PFMA/homoPS blend were swollen with CO₂ and showed OOT from as-cast state cylinders to lamellae at 10 MPa. However, as the pressure increased, neat PS-PFMA showed a phase transition from lamellae to a 100 nm-order “foam” structure instead of the typical inverted phases. On the other hand, the copolymer/homopolymer blend was transformed into a PFMA/CO₂-rich inverted phase such as a sponge-like bicontinuous structure.