Source: soft matter

Artificial muscle is a new type of intelligent shape memory material, which can stretch, bend, tighten or expand through the change of the internal structure of the material. At present, the commonly used artificial muscle materials are piezoelectric ceramics, shape memory alloys, electroactive polymers and so on. Recently, the reporter learned from Southeast University that Professor Yang Hong’s research group of the school of chemistry and chemical engineering of the university has developed a polyurethane / polyacrylate interpenetrating network structure liquid crystal elastomer material, which has super mechanical properties, breaks through the research bottleneck of 40 years, and has a wide application prospect in artificial muscle and other fields. The research results were recently published in the international journal Annals of the American Chemical Society.

Liquid crystal elastomer is a typical bi-directional shape memory material, which has the advantages of large and reversible deformation. It has a good application prospect in bionic devices, soft robots and other fields. However, after 40 years of development, the study of liquid crystal elastomers remains at laboratory level, and has not been industrialized.

Liquid crystal elastomer was developed 40 years ago, said Yang Hong. 20 years ago, people realized that it can be used as a high-quality material for artificial muscle. “As the best bidirectional shape memory material, liquid crystal elastomer has large shape variable, can be compressed from 100cm to 20cm, and has fast deformation speed, which is more advantageous than piezoelectric ceramics and other materials.”

However, the key scientific problem limiting its application is that the stress amount produced by the liquid crystal elastomer in the deformation process is too small to meet the mechanical performance requirements of the actual application scenarios. Yang Hong said: “a very important index affecting the stress is the elastic modulus. At present, the deformation elastic modulus of liquid crystal elastomers studied both at home and abroad is only a bit more than 1 MPa. If they want to be used as artificial muscles, there should be at least 10 MPa.”

Professor Yang Hong’s research team took a new approach to prepare a polyurethane / polyacrylate interpenetrating network structure liquid crystal elastomer material by mixing the small molecular precursor components of polyurethane liquid crystal elastomer and polyacrylate liquid crystal thermosolid, and then perform synchronous crosslinking. Its shrinkage strain percentage, stress amount and elastic modulus amount reached 46%, 2.53 MPa and 10.4 MPa, respectively. For the first ever time, the mechanical properties of liquid crystal elastomer based artificial muscle are fully met, and the technical bottleneck in this field is broken.