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Characterization of the soft behavior of nematic elastomers over a range of temperature and strain rates

Alice Kutsyy, Adeline Wihardja, Victoria Lee, Kaushik Bhattacharya

TL;DR

This work investigates the soft-elastic response of isotropic-genesis polydomain nematic elastomers (I-PLCEs) across a broad range of temperatures, strain rates, and cross-link densities, using a newly developed tensile testing setup with in-situ 2D-DIC. The authors document a pronounced polydomain-monodomain transition–driven soft plateau below the nematic-isotropic transition temperature $T_{ni}$, whose plateau stress and extent depend on temperature, strain rate, and cross-link density; above $T_{ni}$ the plateau vanishes and the response becomes network-dominated. A macroscale constitutive model incorporating two internal variables $(\Lambda, riangle)$ to describe domain pattern evolution accurately fits the loading data across conditions and provides a predictive framework for design. The findings highlight the coupled influence of thermal, rate-dependent, and network effects on soft elasticity in I-PLCEs and offer a pathway toward thermo-mechanically informed engineering applications, while noting the isothermal scope of the current study and suggesting future thermo-mechanical integration.

Abstract

Nematic elastomers are a particular class of liquid crystal elastomers (LCEs) that exhibit both liquid-crystalline order and rubber (entropic) elasticity. This combination makes them stimuli-responsive soft materials with a number of unusual thermo-mechanical properties. They have been proposed for various applications, including soft robotics, enhanced adhesion, and impact resistance. This paper presents a new experimental setup and a comprehensive dataset characterizing the soft behavior of nematic elastomers over a range of temperatures and strain rates. We also fit the results to a recently developed model of nematic elastomers.

Characterization of the soft behavior of nematic elastomers over a range of temperature and strain rates

TL;DR

This work investigates the soft-elastic response of isotropic-genesis polydomain nematic elastomers (I-PLCEs) across a broad range of temperatures, strain rates, and cross-link densities, using a newly developed tensile testing setup with in-situ 2D-DIC. The authors document a pronounced polydomain-monodomain transition–driven soft plateau below the nematic-isotropic transition temperature , whose plateau stress and extent depend on temperature, strain rate, and cross-link density; above the plateau vanishes and the response becomes network-dominated. A macroscale constitutive model incorporating two internal variables to describe domain pattern evolution accurately fits the loading data across conditions and provides a predictive framework for design. The findings highlight the coupled influence of thermal, rate-dependent, and network effects on soft elasticity in I-PLCEs and offer a pathway toward thermo-mechanically informed engineering applications, while noting the isothermal scope of the current study and suggesting future thermo-mechanical integration.

Abstract

Nematic elastomers are a particular class of liquid crystal elastomers (LCEs) that exhibit both liquid-crystalline order and rubber (entropic) elasticity. This combination makes them stimuli-responsive soft materials with a number of unusual thermo-mechanical properties. They have been proposed for various applications, including soft robotics, enhanced adhesion, and impact resistance. This paper presents a new experimental setup and a comprehensive dataset characterizing the soft behavior of nematic elastomers over a range of temperatures and strain rates. We also fit the results to a recently developed model of nematic elastomers.

Paper Structure

This paper contains 17 sections, 3 equations, 10 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Experimental methods
  3. Experimental setup
  4. Liquid Crystal Elastomer Synthesis
  5. Experimental observations
  6. Tests on specimens with cross-linker density 50 mol%
  7. Tensile tests at room temperature (26)
  8. Tensile tests at 55
  9. Tensile tests at 90
  10. Comparison across temperatures
  11. Cross-linker density 25 mol%
  12. Fit to a macroscale constitutive model
  13. Conclusion
  14. Conflict of interests.
  15. Acknowledgements.
  16. ...and 2 more sections

Figures (10)

  • Figure 1: (a) The temperature-driven isotropic to nematic transition and the resulting deformation in nematic elastomers. (b) The multiscale nature of I-PLCEs; a typical specimen consists of numerous domains of varying nematic orientation.
  • Figure 2: Stress-strain curve demonstrating LCE soft behavior. Plateau stress, elastic response, and residual strain are labeled.
  • Figure 3: The experimental setup and typical result. (a) Schematic diagram, (b) the overall setup (c) the heated chamber, and (d) a typical DIC result.
  • Figure 4: Room temperature tensile tests for 50 mol% cross-linker density. (a) Test to failure for a number of batches, and
  • Figure 5: 55$^\circ$C tensile tests for 50 mol% cross-linker density at various strain rates. (a) Tests to failure, and (b) load-unload tests.
  • ...and 5 more figures