Reprocessable Thermoset Soft Actuators

Abstract

Widely used traditional thermosets are good candidates for construction of 3D soft actuators because of their excellent stability; however, it is generally acknowledged that they cannot be reprocessed. The time–temperature equivalence principle enables reprocessing of traditional liquid crystalline epoxy thermosets (LCETs) into 3D soft actuators. Even though the transesterification reaction of LCETs is extremely slow, it is fast enough to induce a topology rearrangement and subsequent reprocessing when prolonging the transesterification time according to aforementioned principle. Therefore, LCETs can be aligned by a simple procedure. The alignment is quite stable at high temperature and remains after more than 1000 heating–cooling actuation cycles. The resulting 3D soft actuators are remouldable, reprogrammable, reconfigurable, weldable, self‐healable, recyclable, and stable, which is impossible for any traditional thermosets and is therefore a compelling advance in terms of the applications open to 3D soft actuators.

Liquid‐Crystalline Soft Actuators with Switchable Thermal Reprogrammability

“…However, as for the aligned actuator in which TMA‐DMSiO had not been deactivated, degradation of thermal actuation was obviously observed after the first cooling–heating cycle (Supporting Information, Figure S17). Notably, our strategy to switch off network dynamics for attaining thermal and actuation stability is essentially different from the previous strategies that just slow down the bond exchange rate at high temperatures in LCEs . Our strategy directly eliminates the siloxane bond exchangeability in the network.…”

“…LCEs can convert external stimuli into reversible mechanical actuation after installing liquid‐crystal alignment, which is an outstanding material of choice for soft actuators . For thermally reprogrammable LCEs, topology change of the network stems from the introduction of dynamic covalent chemistry, for example, transesterification and disulfide metathesis . The same as mentioned above, it is very difficult to attain good thermal reprogrammability and stability at the same time in LCEs.…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…Recently, 3D printing has allowed for the construction of LC‐based actuators having pre‐designed initial shapes . The ability to shape fix the starting geometry into any arbitrary shape and subsequently trigger reversible actuation through exposure to light, as done for temperature‐driven actuators through shape memory or by using dynamic covalent bonds, remains largely unexplored. Light encoding has been employed by Priimagi and co‐workers as an approach towards photo‐rewritable programming of light‐driven actuation in LCNs .…”

Liquid‐Crystalline Soft Actuators with Switchable Thermal Reprogrammability

“…In all of the previous systems, as long as thermally triggered bond exchange exists, the risk of actuation loss and shape distortion always exists at work and in storage, which is not satisfactory for applications that demand creep resistance at elevated temperature. The unwanted thermally induced bond exchange can be slowed down, but it cannot be eliminated …”