Mechanics of Liquid Crystal Elastomer

Integrating liquid crystal molecules into a crosslinked polymer network can result in a rubber -like material, which is often named as liquid crystal elastomer. Because of its special molecular structure, many interesting properties and behaviors have been found in liquid crystal elastomers such as soft or semisoft elasticity,  opto-mechanical coupling, electro-mechanical coupling and stripe domain instability. Novel engineering applications of liquid crystal elastomers have also recently emerged such as artificial muscles, soft robots, stretchable rubber laser and shock absorbing structures.

In the presentation, I will discuss several of our recent studies on the mechanics of liquid crystal elastomers. The first is a light-driven liquid crystal elastomer tensegrity robot, which is ultralight, highly scalable, has high load capacity, and can be precisely controlled to move along different paths on multiple terrains.

Inflation of an elastomer balloon is one of the most classical and important problems in the field of nonlinear elasticity. The second study is anomalous inflation of a cylindrical liquid crystal elastomer balloon. We found in the experiment that with a small increment of inflating pressure, the balloon contracts significantly along its axial direction while expands in its radial direction. With further increase of the pressure, the balloon expands mainly in the radial direction while maintains its length almost unchanged. Finally, the balloon expands both in the radial and axial directions abruptly with a tiny increase of inflating pressure, often leading to rupture of the balloon. The experimental phenomenon can be well explained by the theory.

The third is electrically controlled liquid crystal elastomer–based soft tubular actuators with multimodal actuation. Controlled by an externally applied electrical potential of several volts, the tubular actuator can exhibit multidirectional bending as well as large (~40%) homogenous contraction. Using multiple tubular actuators, we further build a multifunctional soft gripper and an untethered soft robot.

The fourth is transiently crosslinked liquid crystal elastomer. We demonstrate that the dynamic covalent bonds in the elastomer enables its programmability, reprocess ability, self-healing capability and recyclability.  

The last is the necking phenomenon of a monodomain liquid crystal elastomer subject to a uniaxial stretch. We found in the experiments that when the applied strain rate is high enough, one or several necks can form and propagate in the elastomer with the increase of the stretch. To explain the necking phenomenon, we adopt a viscoelastic constitutive model of the liquid crystal elastomer. In the model, the viscosity of the elastomer is regarded as a function of the orientation of the mesogens.