Dependence of size and morphology on shear flow for PS-based amphiphilic block copolymer micelles in aqueous solution

Abstract

This contribution focuses on the impact of shear flow on size and nanostructure of PS-based amphiphilic block copolymer (BC) micelles by varying the stirring rate and copolymer composition. The results show that the vesicles formed from diblock copolymer (di-BC) of PS-b-PAA remain with vesicular morphology, although the average size decreases, with the increase of stirring rate. However, the multi-compartment micelles (MCMs) formed from tri-block copolymer (tri-BC) of PS-b-P2VP-b-PEO are quite intricate, in which the copolymer first self-assembles into spheres, then to clusters, to large compound micelles (LCMs), and finally back to spheres, as stirring rate increases from 100 r/min to 2200 r/min. Formation mechanism studies manifest that vesicles form simultaneously as water is added to the di-BC solution, termed as directassembly, and remain with vesicular structure in the flowing process. While for the PS-b-P2VP-b-PEO copolymer, spherical micelles at initial stage can further assemble into clusters and LCMs, termed as second-assembly, due to the speeding-up-aggregation of the favorable stirring. As a result, an invert V-relationship between tri-BC micelle dimension and stirring rate is observed in contrast to the non-linear decreasing curve of di-BC vesicles. It is by investigating these various amphiphilic BCs that the understanding of shear dependence of size and morphology of micelles is improved from self-assembly to second-assembly process.