Synthesis And Performance Study Of High-strength Self-healing Liquid Crystal Elastomer Materials

Liquid crystal elastomers(LCEs)are a class of flexible smart materials that can undergo large reversible deformation in response to external stimuli,and are used in a wide range of applications such as artificial muscles,actuators,and bionic materials.However,the existing LCEs have low mechanical strength,which limits their practical applications.In addition,as flexible drive materials,damage to LCEs during application will severely shorten their loading,reversible deformation stability and service life.In this paper,three high-strength self-healing LCEs were carried out to address the above issues and their potential practical applications were investigated.The details of the study and the main findings are as follows.1.To improve the mechanical properties of LCEs and give the material the ability of self-healing,we introduced(2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate)(Upy MA)containing quadruple hydrogen bonds into the cross-linked network of LCEs in the form of side chains and prepared a double cross-linked network liquid crystal elastomers(U-LCEs)with chemical cross-linking as the main part and physical cross-linking as the supplement.The mechanical properties of the prepared U-LCEs were effectively improved with tensile strength up to 8.5 MPa.the thermal actuation capacity of the U-LCEs was excellent by two tensile collimation,with reversible shrinkage up to50%and a driving work capacity of 121.2 k J/m~3,which is three times higher than that of mammalian muscle(40 k J/m~3).The electrostatic adsorption of quadruple hydrogen bonds not only improves the mechanical properties of U-LCEs,but also imparts self-healing ability to the material.2.In order to further improve the mechanical properties of LCEs,especially the actuation ability at high temperatures.In this section,a high-strength,high-temperature resistant polyurethane was prepared using a one-step method to interpenetrate the cross-linked network of LCEs to develop a high-strength interpenetrated structural liquid crystal elastomer composite(PTPU-LCEs).The synthesized polyurethane has a tensile strength of 26 MPa at room temperature and 6.1 MPa at high temperature.However,the interpenetrating network can damage the original mechanical properties of the material.In order to reduce the damage of the interpenetrating network to the mechanical properties of the material,the tensile strength of the prepared composites can reach 10 MPa at room temperature and 1.9 MPa at high temperature by regulating the content of polyurethane,which is 2.7 times of the common LCEs.The thermotropic deformation rate of PTPU-LCEs is 40.6%,which can lift an object 1250 times heavier than itself.In addition,the PTPU-LCEs-CNT/CB composite foam was prepared by using sodium chloride to make holes in the composite material and attaching CNT/CB on its surface.The resistive strain sensor prepared based on the composite foam has good sensitivity and expands the application range of LCEs.3.In order to improve the mechanical properties of azobenzene-based LCEs,bis-hydroxyazobenzene AZO-OH was synthesized as a chain extender and UPy-OH containing quadruple hydrogen bonds as a cross-linking agent,and high-strength azobenzene liquid crystal polyurethanes were prepared by a one-step method.The cross-linked network contains a large number of benzene rings with hydrogen bonds,increasing its tensile strength to 25 MPa.The synthesized azobenzene liquid crystal polyurethanes have the properties of azobenzene-type photo-responsive materials,i.e.,cis-trans isomerization of the azobenzene structure under UV light to achieve the light-driven capability of azobenzene liquid crystal polyurethanes.The quadruple hydrogen bonding with the carbamate group enables the self-healing of the material.