A Programmable Liquid Crystal Elastomer Metamaterials With Soft Elasticity

Abstract

Liquid crystal elastomers (LCEs) are a rubbery network of polymers with ordered liquid crystal mesogens. The combination of rubber elasticity and the anisotropic liquid crystalline order gives exceptional mechanical properties, like soft elasticity, where near-constant stress accompanies large elastic deformation in the material. However, the soft elasticity in LCEs is often bounded by the intrinsic molecular interactions and structures, limiting the range of programmable mechanical properties and functionalities. Here, we demonstrate that the semi-soft elasticity of LCEs can be integrated into the framework of metamaterials to realize markedly programmabilities. Under uniaxial deformation, each state of the building blocks in metamaterials and the molecular composition of the nematic LCEs is associated with a distinctly different stress-strain relation that is fully elastic. Taking advantage of the tunable bending and stretching deformation enabled by the geometry of the building blocks and the semi-soft elasticity of the nematic LCE in the metamaterials, we can engineer the local stretch and stress at an unmet level of their counterpart composed by elastomers. Numerical simulations and analytical models are developed to relate the metamaterial geometries and the LCE soft elasticity to the mechanical responses. In addition, an elastic region with near-zero stiffness up to a stretch of 1.4 can be designed by connecting the compliant responses due to bending deformation and the soft elasticity in the LCE. We expect that the specialized mechanical tunability enabled by the LCE metamaterials can facilitate the development of advanced forms of mechanical metamaterials and impact the design of robotic systems.

Recent Trends in Continuum Modeling of Liquid Crystal Networks: A Mini-Review

“…For instance, anomalous inflation behaviors of a nematic balloon, e.g., inflation-induced torsion, are described theoretically as shown in [41,42]. Recently, Liang and Li [43] presented a theoretical model of LCN-based metamaterials; by combining a molecular description of the soft elasticity and numerical simulations, the study shows that LCN metamaterials have a compliant response to lightinduced bending, which leads to a transition between strain-softening and strain-stiffening with different effective shear moduli. The authors also develop an analytical model to predict the local stretch in a ligament and force in LCN metamaterials, relating the softening and stiffening responses to the geometric and material parameters.…”

Photothermal-Driven Liquid Crystal Elastomers: Materials, Alignment and Applications

“…As a popular smart material, LCE have attracted widespread attention due to their stimulus responsiveness and programmability [ 4 , 32 , 69 , 71 , 72 , 73 ]. Photothermal-driven LCE is a competitive strategy because it can achieve remote control, wavelength selection, and accurate actuation.…”

Dynamic large strain formulation for nematic liquid crystal elastomers

“…In this way, they separated the dissipations due to the rotations of the mesogens and to the inherent viscoelasticity of the elastomer and compared their model with experimental results of Martin Linares et al [12] in terms of rate-dependency. Liang and Li [13] explored the tunability of metamaterials by exploiting the semisoft elasticity of nematic LCEs. Semisoft elasticity was modeled by adding a term depending on fluctuations in the ordering of the nematic LCE to the trace formula of Warner and Terentjev [1,14].…”