Structural inversion of micellar block copolymer thin films

Polystyrene-b-poly(1,1', 2,2'-tetrahydroperflurooctyl methacrylate) (PS-b-PFOMA) thin films, cast from a cosolvent mixture of Freon 113 and toluene onto Si/SiOx substrates, form spherical micelles; the cores are composed of PFOMA chains with a PS corona. Upon exposing the films to supercritical CO2 (Sc-CO2), the morphology inverts, wherein the core is composed of PS chains and the PFOMA chains constitute the corona. In each case, the free surface and polymer/substrate layers are enriched with PFOMA. The size of the PS cores is found to increase with decreasing Sc-CO2 activity. This size variation is discussed in light of recent theoretical developments that account for the effect of Sc-CO2 activity on PS-CO2 interfacial tension and chain stretching of the corona versus the core.