Photo-thermo-mechanically actuated bending and snapping kinetics of liquid crystal elastomer cantilever

Abstract

A composite of liquid crystal elastomer (LCE) incorporated with carbon nanotubes (CNTs) can convert absorbed photon energy into thermal energy to trigger the phase transition of the LCE, resulting in photo-thermo-mechanically actuated devices. We model the transient temperature distribution and the bending kinetics of a straight cantilever beam actuator under the radiation of a laser diode (LD) light. Three possible bending modes of the beam for various LD light powers are identified. The temperature distribution and the bending modes are found to be in good agreement with the reported experimental observations. The underlying deformation mechanisms and bending modes are manifested by probing the stress evolution and propagation of nonzero stress regions during the bending process. For a beam that is initially slightly curved, we also predict the possibility of snap-through instability, and three typical phases of snapping are captured. This procedure paves the way for the design of LCE-based soft actuators.

Light‐Driven Carbon‐Based Soft Materials: Principle, Robotization, and Application

“…For example, the single‐layer carbon/liquid crystal composite film was reported with the light‐driven bending performance. [ 83,57,84 ] When applying light exposure, the film's surface which is directly exposed to the light exposure had a higher temperature variation, whereas the opposite surface of the film had a lower temperature, leading to the inhomogeneous temperature distribution within the film. Then, the inhomogeneous contraction would cause a bending deformation in the actuator, for example, the LCE/CNT actuator shown in Figure 3g.…”

Modeling of Light-Driven Bending Vibration of a Liquid Crystal Elastomer Beam

“…where x j ¼ b 2 j , f j ¼ a=2x j , and P j ðtÞ ¼ Y 0 j ð1ÞmðtÞ. The solution of ordinary differential equation (16), with initial conditions (12) and (13), can be given by Duhamel integration…”

“…In particular, some photochromic liquid crystal molecules such as azobenzenes can transform from straight trans configuration to bent cis configuration by absorbing UV light. As a result, an LCE, containing azobenzenes, can deform under UV light radiation, because the variation of molecular configuration of azobenzenes can change the order degree of liquid crystal molecules, and thus induce strain in LCEs [15][16][17][18]. Different from many other external stimuli, one can control light source remotely and precisely focus light on different regions of a material.…”

Thermoplastic Elastomers with Photo-actuating Properties

“…Another additive, which can considerably improve the photo-actuating properties of the LCEs, are carbon nanotubes (CNTs). CNTs are efficiently applied due to their one-dimensional shape, nanoscale diameters, large surface area, and excellent electrical and thermal properties [34,35]. Special case of carbon nanotubes effectively applied in photo-actuating systems are singlewalled carbon nanotubes (SWCNTs) exhibiting strong absorptions in the visible and near-IR region [36].…”