Abstract
The bilayer structure consisting of thermal-responsive liquid crystal elastomers (LCEs) and other polymer materials with stretchable heaters has attracted much attention in applications of soft actuators and soft robots due to its ability to generate large deformations when subjected to heat stimuli. A simple analytical thermo-mechanical model, accounting for the non-uniform feature of the temperature/strain distribution along the thickness direction, is established for this type of bilayer structure. The analytical predictions of the temperature and bending curvature radius agree well with finite element analysis and experiments. The influences of the LCE thickness and the heat generation power on the bending deformation of the bilayer structure are fully investigated. It is shown that a thinner LCE layer and a higher heat generation power could yield more bending deformation. These results may help the design of soft actuators and soft robots involving thermal responsive LCEs.
Highlights
IntroductionLiquid crystal elastomers (LCEs), made of cross-linked networks of polymers with mesogenic units, combine mechanical properties of rubbers with nematic characteristics of liquid crystals[1,2,3] and can provide large deformations through phase transition when subjected to external stimuli (e.g., light and heat).[4,5,6,7,8,9,10,11,12] For example, the thermal responsive LCEs exhibit shrinking when heated up to a temperature higher than the phase transition temperature where a transition from the liquid crystalline phase to isotropic state occurs.[10]
In order to validate the analytical solutions for the temperatures in Eq (7) and the radius of bending curvature in Eq (13), finite element analysis (FEA) is performed using ABAQUS software via the continuum element C3D8RT to study the thermo-mechanical behavior of the bilayer structure
A thermo-mechanical analytical model is established to predict the temperature increase and bending behavior of the bilayer structure consisting of the Liquid crystal elastomers (LCEs) layer, the open-meshed heater and the PI layer
Summary
Liquid crystal elastomers (LCEs), made of cross-linked networks of polymers with mesogenic units, combine mechanical properties of rubbers with nematic characteristics of liquid crystals[1,2,3] and can provide large deformations through phase transition when subjected to external stimuli (e.g., light and heat).[4,5,6,7,8,9,10,11,12] For example, the thermal responsive LCEs exhibit shrinking when heated up to a temperature higher than the phase transition temperature where a transition from the liquid crystalline phase to isotropic state occurs.[10]. Wang et al.[24] fabricated an adaptive soft robot, consisting of actuators of open-mesh shaped thin deformable resistive heaters and thermal responsive artificial muscles of a bilayer structure. L0 where L0 denotes the initial dimension along length direction of LCE under the temperature around 30 oC without any thermal-induced deformation while L(T ) represents the length dimension under temperature T. The measurement of both L0 and L(T ) under different temperature is developed on the hot plate. Required parameters of Eq (1) can be measured from pictures and shrinking strains are obtained
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