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Microfluidic Preparation of Liquid Crystalline Elastomer Actuators
Published on: May 20, 2018
Nematic fluctuations and semisoft elasticity in liquid-crystal elastomers
1Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia.
Summary
We developed a theory for nematic fluctuations in liquid-crystal elastomers (LCEs), revealing that bend modes act as soft modes detectable via dynamic light scattering (DLS) at threshold strain, unlike splay modes.
Area of Science:
- Soft Matter Physics
- Materials Science
- Polymer Physics
Background:
- Liquid-crystal elastomers (LCEs) exhibit a nematic state through orientational symmetry breaking.
- Ideal LCEs possess a coupled director-shear soft mode (Goldstone mode) with zero relaxation rate at long wavelengths.
- Nonideal LCEs with locked-in anisotropy show finite relaxation rates for these modes.
Purpose of the Study:
- To develop a detailed theory of nematic fluctuations in LCEs.
- To calculate relaxation rates of director modes using dynamic light scattering (DLS).
- To investigate the influence of deformation and crosslinking density on director relaxation properties.
Main Methods:
- Theoretical modeling using the semisoft model of Gaussian elasticity.
- Derivation of relaxation rates as a function of deformation for various scattering geometries.
- Experimental validation using dynamic light scattering (DLS) measurements on LCE samples.
Main Results:
- The bend-mode relaxation rate approaches zero at the threshold strain, identifying it as the soft mode.
- The splay-mode relaxation rate remains finite at the threshold strain, indicating it is not a soft mode.
- Experimental DLS measurements on LCE samples with varying crosslinking densities align with theoretical predictions.
Conclusions:
- The semisoft model accurately predicts director relaxation properties in nonideal LCEs.
- Bend modes function as soft modes in LCEs under deformation, becoming detectable at elastic instability.
- Director relaxation behavior in side-chain LCEs is largely independent of crosslinking density.
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