The Origins of Toroidal Micelles from a Liquid–Crystalline Triblock Copolymer^†

In this paper, we reported a systematic study on the formation mechanism of bent toroidal micelles from a triblock copolymer poly(acrylic acid)-block-(2-cinnamoyloxylethyl methacrylate)-block-poly(perfluorooctylethyl methacrylate) (PAA-b-PCEMA-b- PFMA) in the binary solvent mixture of methanol and α,α,α-trifluorotoluene (MeOH/TFT) through a heating-cooling procedure. It was found that the formation process of toroids was predominantly kinetic-controlled, and can be influenced by the preparation protocol, solvent composition and stirring rate of the solutions. The toroids were formed via a complicated morphological transition process. At high temperature, the polymer formed bilayered vesicles with bumpy surface, while upon cooling, the vesicles broke and unfolded into bumpy platelet micelles, which subsequently perforated into toroidal and cylindrical micelles upon further cooling. Besides the distinct and unique bumpy vesicle and platelet structures, the transformation mechanisms from vesicular to platelet, and toroidal micelles are also very intriguing, and may provide new insights into the interconversion of micellar morphologies.