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

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.