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Liquid crystalline elastomers (LCEs) exhibit reversible macroscopic shape changes in response to a temperature change. Mechanistically, the thermomechanical response of LCEs is associated with the thermotropic nature of the liquid crystalline units (i.e., mesogens) in the polymer network. Upon heating, the mesogen‐mesogen interaction in the LCE is disrupted, which transitions the organization of the polymer network from an ordered to a disordered state. The disruption in order affects the volumetric distribution of macromolecular chains in the polymer network and results in a large directional contraction along the alignment axis. Prior reports detail that the magnitude of actuation depends strongly on the connectivity of LC mesogens (i.e., main‐chain or pendant) within the network. In this study, pendant end‐on mesogens are introduced into a primarily main‐chain supramolecular LCE composition to further reduce crosslink density while preserving overall LC concentration. The introduction of pendant end‐on mesogens to supramolecular LCE compositions further improves thermomechanical properties by enhancing strain‐temperature coupling and reducing actuation temperatures. By systematically varying the concentrations of end‐on and supramolecular mesogens, direct relationships are established between mesogen composition, polymer architecture, and the resulting thermomechanical performance of LCEs.
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Coupling between viscoelasticity and soft elasticity in main-chain nematic Liquid Crystal Elastomers
Liquid crystal elastomers (LCEs) are a class of smart elastomers exhibiting unusual mechanical behavior, including large energy dissipation and soft elasticity under uniaxial tensile loading. LCEs are composed of liquid crystal molecules, called mesogens, linked by a network of polymer chains. During deformation, the mesogens orient in the direction of the loading, leading to soft elasticity, which is an increase in strain at constant stress. The combination of mesogen rotation and intrinsic polymer viscoelasticity leads to a nonlinear viscoelastic soft elastic behavior. The aim of this paper is to investigate the coupling between the viscoelastic mechanisms and soft elasticity in main chain LCEs. We propose a rheological model in which the mesogen rotation during deformation is represented by a reversible slider while viscoelastic relaxation mechanisms are modeled as series of Maxwell elements coupled or decoupled with mesogen rotation. Fitting this model to experimental data demonstrate that the coupling between polymer chain viscoelasticity and mesogen rotation is partial, i.e. the long-time relaxation mechanisms are coupled and the short-time relaxation mechanisms are decoupled from mesogen rotation. Furthermore, we show that the viscosity of mesogen rotation is not necessary to properly predict the elastic modulus during the soft elasticity but it is needed to properly predict the initiation of the phenomenon. \end{abstract}
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- Award ID(s):
- 2238035
- PAR ID:
- 10504286
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of the Mechanics and Physics of Solids
- Volume:
- 187
- Issue:
- C
- ISSN:
- 0022-5096
- Page Range / eLocation ID:
- 105612
- Subject(s) / Keyword(s):
- Liquid crystal elastomers soft elasticity viscoelasticity mesogen polydomain-monodomain transition constitutive modeling
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jmps.2024.105612
