Double-layered Actuator Research Articles

A bi-directional thermal-driven actuator with conduction‐to‐insulation transformation behavior and its applications in overheating protection and early warning of fire

To endow an actuator with multi functions in response to heat, a layer of electrically conductive silicone rubber (SR) filled with 80 wt% silver powder was coated on a double-layered actuator consisting of two layers of SR filled with different thermal expansion microspheres to obtain a triple-layered actuator. The layer of electrically conductive SR had a little effect on the actuation properties of the triple-layered actuator. The triple-layered actuator exhibited bi-directional deformation and conduction‐to‐insulation transformation behavior during actuation process. The relationships between electrical conductivity, bending curvature and heating time were established. Applications of the actuator in overheating protection and early warning of fire were demonstrated.

From two-dimensional to three-dimensional structures: A superior thermal-driven actuator with switchable deformation behavior

Inspired by origami, 3D structures constructed from 2D structures have increasingly attracted attention, which have potential applications in many fields. Herein, a novel double-layered actuator was fabricated by adding different thermo-responsive thermal expansion microspheres, expanding at low temperature (L-TEMs) and at high temperature (H-TEMs), into different silicone rubber layers. Due to the expansion of L-TEMs and H-TEMs at 120 and 170 °C, respectively, the active and passive layers could exchange at different temperatures, showing switchable deformation behavior. Compared with traditional double-layered actuators, the actuator with the switchable active layers is capable of providing additional functionality. The two layers were assembled by crosslinking the silicone rubber at the interface of the two layers, which endows the good stability of the double-layered actuator. The 2D double-layered structures of the actuators could be transformed into complex 3D structures by heating. In addition, the actuation time was shortened by adding 50 phr alumina due to the enhancement of thermal conductivity and the limited increase in Young’s modulus. This work could pave a way to the design and preparation to high-performance actuators with multiple functions.

Actuation From Directional Deformation Based on Composite Hydrogel for Moisture-Controllable Devices

Reconfigurably adaptive devices through the shape change offer reasonably appropriate and recoverable departures in shape, in order to satisfy changing environmental constraints or operational demands. Here, we demonstrated the humidity-responsive directional-deformation actuators based on interpenetrating composite polymer hydrogel, which were applied as moisture-controlled automatic curtain and power-OFF safety switch. In the double-layer actuators, a rigid stripe of interpenetrating polymer hydrogel by photolithography were aligned into humidity-responsive hydrogel. Through adjusting the angle of interpenetrating polymer stripe, the strip actuators deformed in various deformation orientations, including horizontal, perpendicular, left-handed helix, and right-handed helix deformation with different angles. The directional-deformation actuators were suitable as environmentally adaptive devices in the automatically roll-up and fall-down “curtain” application corresponding to humidity change, and automatically power-OFF safety switch when ambient humidity suddenly increased. These examples of model application exhibited potential significance of the actuators as soft robots.

Bioinspired Hygromorphic Actuator Exhibiting Controlled Locomotion.

We report a bioinspired hygromorphic double-layered actuator (HDA), of which the movement is controlled by cyclical changes in relative humidity (RH). The basic principle of the HDA lies in the rapid swelling and deswelling of highly hygroscopic layer-by-layer (LbL) assembled films deposited on a moisture-resistant and flexible polytetrafluoroethylene (PTFE) ribbon. We engineer the geometry of the HDA to induce locomotion on a ratchet track. By controlling the exposure time and RH, the HDA is remotely controlled to move a precise number of steps on the ratchet track during one cycle of RH changes. We demonstrate that the step length of the HDA depends on the relative thickness change of the LbL film. We also provide theoretical considerations based on a plate theory and the Flory-Huggins theory to describe the actuation of the HDA. Our work provides fundamental insights into the fabrication and design of hygromorphic actuators driven by RH changes.