4D printing of fast‐responsive liquid crystalline elastomers for light‐driven actuators

Among smart materials, Liquid Crystalline Elastomers (LCEs) combine programmable well-defined deformations with wireless control. To date, the successful fabrication of LCEs through 3D printing techniques, such as direct ink writing (DIW), requires precise control over the ink formulation, mesogen alignment, and curing processes, to get devices with uniform molecular orientations, and with optimized actuation performance. Here, we present a simple synthetic approach leading to a ten-of-gram-scale ink production suitable for low-cost DIW 3D printing of LCEs. The novel ink, containing a push-pull azobenzene directly linked to the polymer backbone, enabled 4D printing of fast responsive photo-mechanical actuators with programmable and reversible deformation. Our centimeter-scale LCE structures present active tensions twitches comparable to those of cardiac muscles, both in terms of magnitude (kPa range) and timescale (tens to hundreds of milliseconds). An all-round actuation characterization is also developed and reported. As a proof-of-concept demonstrator, an optical beam steerer was developed demonstrating a high control of the beam diffraction angle as a function of the control beam light power.