Liquid crystal and crystal are two common material structures, which have many differences. Crystalline molecules can crystallize into lattice with high cohesive energy and can undergo epitaxial growth. The liquid crystal has an orientational or positional order in a certain direction. These ordered liquid crystal components have a high fluidity at the same time and show many unique properties. It can be said that liquid crystal is an intermediate material structure between crystal state and liquid state.In the past ten years, polymer scientists have successfully achieved controllable self-assembly of various crystalline copolymers with crystallization driving force and obtained rich morphologies, complex structures, and multi-dimensional nanostructures. These assembly methods are called crystallization-driven self-assembly (CDSA). In recent years, liquid-crystallization-driven self-assembly (LCDSA) has also emerged and attracted attention. However,the driving mechanism and regulation strategy of the liquid crystallization system are still not clear due to the fundamental difference between liquid crystallization and crystallization.
Recently, Prof. Jiaping Lin and his group at the School of Materials Science and Technology of East China University of Science and Technology have made new progress in the research of controlled micelle growth and termination by liquid-crystallization-driven self-assembly. Through the self-assembly experiments and molecular dynamics simulation of PBLG-b-PNIPAM (poly(γ-benzyl-L-glutamate)-b-poly(N-isopropyl acrylamide)), it is found that the fluidity of liquid crystal and the interaction strength between the liquid crystal are the keys to achieve the controlled growth and termination of the liquid crystal structure.
In this research work, cylindrical micelles with cholesteric liquid crystal cores are used as seeds. After adding block copolymers, the copolymers form new aggregates, and the seed micelles undergo epitaxial growth after fusing with the seeds. During this growth process, the rigid segments in the aggregate rearrange, so that the living ends maintain the cholesteric liquid crystal arrangement consistent with the seed cores. Therefore, the fluidity of liquid crystals is the key to this growth behavior. In addition, when the interactions between rigid liquid crystal blocks are stronger, and after the aggregates are fused with the seeds, the living ends have the characteristic of the smectic liquid crystal arrangement. At this time, it is difficult for the segments to rearrange and adjust back to the cholesteric liquid crystal arrangement. Therefore, the weak rearrangement ability finally terminates this growth behavior. The research work reported the regulation method of liquid- crystallization-driven self-assembly to realize the controllable growth and termination of micelles, revealed the key driving mechanism of liquid crystal fluidity and reported the termination behavior of micelle controlled growth for the first time, which provided an in-depth understanding and theoretical reference for the controllable self-assembly of copolymers and the accurate construction of nanostructures.
Figure1. Controlled growth and termination of liquid-crystallization-driven self-assembly
The work was completed by young scholar Liang Gao and doctor Hongbing Gao of the East China University of Science and Technology under the guidance of Professor Jiaping Lin, Associate Professor Liquan Wang, and Professor Xiaosong Wang of the University of Waterloo, Canada. The related work was published in Macromolecules(DOI: 10.1021/acs.macromol.0c01820) under the title of "Growth and Termination of Cyclic Miracles via Liquid Crystallization is Driven Self-Assembly". This work has also been strongly supported by researcher Chunming Yang of Shanghai Synchrotron Radiation Facility.
Original link：https://pubs.acs.org/doi/10.1021/acs.macromol.0c01820