Self-assembly of a semi-fluorinated diblock copolymer in a selective solvent

The self-assembly of a highly incompatible siloxane containing semi-fluorinated diblock copolymer, polytrifluoro propyl methylsiloxane-b-polystyrene (SiF-PS), in toluene, a selective solvent for polystyrene, was studied using Small Angle Neutron Scattering. Incompatibility is often enhanced by inserting fluorinated segments into one of the blocks and as a result not only the interchain interactions are changed but also the rigidity of the blocks. Herein the incorporation of siloxane into the backbone of a semi-fluorinated block maintains its flexibility and allows separation of the effects of direct interactions due to fluorine atoms from those of rigidity. Measurements were carried out in dilute solutions below 1 wt%, at volume fractions phi(SiF) ranging from 0.0 to 0.5. The high incompatibility of the SiF block drives aggregation at low volume fractions of the SiF block, where spherical core-Gaussian shell aggregates are detected at phi(SiF) = 0.16. In the symmetric SiF-PS complex fluid, elongated micelles were observed. The micelles exhibited unique temperature stability in comparison with the aggregates formed by diblock-copolymers in the lower segregation regime. As the temperature increases the micelles dissociate into free chains to form unimolecular micelles.