Critical micellisation density: a SAS structural study of the unimer-aggregate transition of block-copolymers in supercritical CO2

In this paper we report a SANS investigation of micelle formation by fluoro carbon-hydrocarbon block copolymers in supercritical CO2 (scCO(2)) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the sol vating ability of scCO(2) by profiling pressure. At high pressure the copol ymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the co re and the fluorocarbon segments forming the corona of spherical aggregates . This aggregate-unimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, thus suggesting the definition of a critical m icellisation density (CMD).