Effects of Operating Mechanical Conditions and Polymer Networks of Nematic Elastomers on Photo-Induced Mechanical Performances

Photoresponsive liquid-crystalline elastomers (LCEs) are promising candidates for light-controlled soft actuators. Photoinduced stress/strain originates from the changes in mechanical properties after light irradiation. However, the correlation between the photoinduced mechanical performance and in-use conditions such as stress/strain states and polymer network properties (such as effective crosslink density and dangling chain density) remains unexplored for practical applications. Here, isometric photo-induced stress or isotonic strain is investigated at different operating strains or stresses, respectively, on LCEs with polymer network variations, produced by different amounts of solvent during polymerization. As the solvent volume increases, the moduli and photoinduced stresses decrease. However, the photo-induced strain, fracture strain, fracture stress, and viscosity increase. The optical response performance initially increases with the operating strain/stress, peaks at a higher actuation strain/stress, and then, decreases depending on the polymer network. The maximum work densities, which also depend on the operating stress, are in the range of approximate to 200-300 kJm-3. These findings, highlighting the significant variations in the mechanical performance with the operating stress/strain ranges and amount of solvent used in the synthesis, are critical for designing LCE-based mechanical devices. Photoisomerization of the azobenzene units incorporated into nematic liquid crystal elastomers induces significant changes in their mechanical properties, including isometric stress or isotonic strain variations. The dependence of their mechanical properties on specified strain or stress conditions and effect of the polymer networks are explored and discussed. image