The Department of Chemistry of Tsinghua University and the Cavendish Laboratory of the University of Cambridge in the United Kingdom published an online title entitled "Mouldable Liquid Crystal Elastomer Driver Through Exchangeable Covalent Bonds" in the internationally renowned journal "Nature Materials" Research papers on liquid-crystalline elastomer actuators with exchangeable covalent bonds) reported that the reversible transesterification reaction was used to successfully prepare moldable, reprocessable liquid crystal elastomer materials. Pei Zhiqiang, a 2012 doctoral student and Yang Yang, a 2012 master student of the Department of Chemistry, Tsinghua University are co-first authors.
Liquid crystal elastomer materials can undergo spontaneous changes in shape under external stimuli such as heat, light, electricity, and magnetism. As actuators and sensors, they have broad application prospects in many fields such as artificial muscles, flexible robots, and blind displays. This shape change is based on the order of the liquid crystal inside the polymer. Changing this order through light, heat, magnetism, etc. will produce a reversible macroscopic shape change. In order to change the actual shape of the liquid crystal elastomer, the liquid crystal polymer chain must be oriented in a single domain (single domain refers to a very narrow or single aligned region in the liquid crystal molecular chain). The traditional two-step cross-linking method, external field and interface condition cross-linking method to prepare single-domain liquid crystal elastomers, or the process is complicated and the success rate is low, or only suitable for micron samples. Because of this, for a long time, this liquid crystal elastomer material is difficult to apply in real life.
This study proposed the idea of ​​using a reversible transesterification crosslinking network instead of a permanent crosslinking network, first to prepare a multi-domain liquid crystal elastomer material with excellent shape memory and processability. On this basis, it is only necessary to stretch the material at a high temperature with a simple mold to orient the liquid crystal cells and cool to normal temperature to obtain a single-domain liquid crystal elastomer. The prepared single domain liquid crystal elastomer not only has a high degree of liquid crystal orientation and excellent mechanical properties, but also can shape different shapes and structures. In the past, it was difficult for liquid crystal elastomers to have other shapes than flat film samples.
The simple method of preparing single-domain liquid crystal elastomer in this study is a major breakthrough in the practical application of liquid crystal elastomers, which opens up the way for the practical application of liquid crystal elastomers as drivers and sensors. For example, the round protrusions shown in the figure, after doping with carbon nanotubes and other substances, can realize the reversible driving of light, which provides the possibility of preparing a liquid crystal elastomer tactile display.
This research was supported by the National Natural Science Foundation of China and the National 973 Project.
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