scholarly journals Nematic liquid crystalline elastomers are aeolotropic materials

2021 ◽  
Vol 477 (2253) ◽  
pp. 20210259
Author(s):  
L. Angela Mihai ◽  
Haoran Wang ◽  
Johann Guilleminot ◽  
Alain Goriely
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
Additional Term ◽  
Elastic Response ◽  
Order Effects ◽  
Nematic Order ◽  
Nematic Elastomers ◽  
Strain Limit ◽  
Liquid Crystal Elastomers ◽  
Dynamics Simulations

Continuum models describing ideal nematic solids are widely used in theoretical studies of liquid crystal elastomers. However, experiments on nematic elastomers show a type of anisotropic response that is not predicted by the ideal models. Therefore, their description requires an additional term coupling elastic and nematic responses, to account for aeolotropic effects. In order to better understand the observed elastic response of liquid crystal elastomers, we analyse theoretically and computationally different stretch and shear deformations. We then compare the elastic moduli in the infinitesimal elastic strain limit obtained from the molecular dynamics simulations with the ones derived theoretically, and show that they are better explained by including nematic order effects within the continuum framework.

scholarly journals Internal constraints and arrested relaxation in main-chain nematic elastomers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Takuya Ohzono ◽  
Kaoru Katoh ◽  
Hiroyuki Minamikawa ◽  
Mohand O. Saed ◽  
Eugene M. Terentjev
Keyword(s):  
Mechanical Properties ◽  
Main Chain ◽  
Polymer Networks ◽  
Nematic Order ◽  
Nematic Elastomers ◽  
Nematic Director ◽  
Highly Nonlinear ◽  
Nonlinear Mechanical ◽  
Liquid Crystal Elastomers ◽  
Memory Applications

AbstractNematic liquid crystal elastomers (N-LCE) exhibit intriguing mechanical properties, such as reversible actuation and soft elasticity, which manifests as a wide plateau of low nearly-constant stress upon stretching. N-LCE also have a characteristically slow stress relaxation, which sometimes prevents their shape recovery. To understand how the inherent nematic order retards and arrests the equilibration, here we examine hysteretic stress-strain characteristics in a series of specifically designed main-chain N-LCE, investigating both macroscopic mechanical properties and the microscopic nematic director distribution under applied strains. The hysteretic features are attributed to the dynamics of thermodynamically unfavoured hairpins, the sharp folds on anisotropic polymer strands, the creation and transition of which are restricted by the nematic order. These findings provide a new avenue for tuning the hysteretic nature of N-LCE at both macro- and microscopic levels via different designs of polymer networks, toward materials with highly nonlinear mechanical properties and shape-memory applications.

Domains In Nematic Elastomers

1993 ◽  
Vol 328 ◽  
Author(s):  
A. Ten Bosch ◽  
L. Varichon
Keyword(s):  
Liquid Crystal ◽  
Mechanical Stress ◽  
Stress Tensor ◽  
Elastic Deformation ◽  
Order Parameter ◽  
Side Chain ◽  
Elastic Model ◽  
Liquid Crystal Elastomer ◽  
Nematic Order ◽  
Nematic Elastomers

ABSTRACTA theory based on an elastic model and including coupling between elastic deformation and nematic order parameter as well as an interaction between crosslinks and orientation is given. The nematic order parameter and the stress tensor have been determined on elongation and as a function of temperature as well as he anisotropy of the conformation of a side chain liquid crystal elastomer on application of a mechanical stress. A transition from a turbid, low ordered polydomain phase to a transparent, Monodomain is shown to occur.

Unsymmetric main-chain liquid crystal elastomers with tunable phase behaviour: elastic response

2011 ◽  
Vol 21 (23) ◽  
pp. 8436 ◽  
Author(s):  
Maria Amela-Cortés ◽  
Duncan W. Bruce ◽  
Kenneth E. Evans ◽  
Christopher W. Smith
Keyword(s):  
Liquid Crystal ◽  
Main Chain ◽  
Phase Behaviour ◽  
Elastic Response ◽  
Liquid Crystal Elastomers

scholarly journals Effect of Shear Rate on the Orientation and Relaxation of a Vanillic Acid Based Liquid Crystalline Polymer

Polymers ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 935 ◽  
Author(s):  
Gijs de Kort ◽  
Nils Leoné ◽  
Eric Stellamanns ◽  
Dietmar Auhl ◽  
Carolus Wilsens ◽  
...  
Keyword(s):  
Shear Stress ◽  
Liquid Crystal ◽  
Shear Rate ◽  
Liquid Crystalline ◽  
Morphological Changes ◽  
Crystalline Polymer ◽  
Elastic Response ◽  
Orientation Parameter ◽  
X Ray ◽  
Break Up

In this study, we report on the visco-elastic response during start-up and cessation of shear of a novel bio-based liquid crystal polymer. The ensuing morphological changes are analyzed at different length scales by in-situ polarized optical microscopy and wide-angle X-ray diffraction. Upon inception of shear, the polydomain texture is initially stretched, at larger strain break up processes become increasingly important, and eventually a steady state texture is obtained. The shear stress response showed good coherence between optical and rheo-X-ray data. The evolution of the orientation parameter coincides with the evolution of the texture: the order parameter increases as the texture stretches, drops slightly in the break up regime, and reaches a constant value in the plateau regime. The relaxation of the shear stress and the polydomain texture showed two distinct processes with different timescales: The first is fast contraction of the stretched domain texture; the second is the slow coalescence of the polydomain texture. The timescale of the orientation parameter’s relaxation matched with that of the slow coalescence process. All processes were found to scale with shear rate in the tested regime. These observations can have far reaching implications for the processing of liquid crystal polymers as they indicate that increased shear rates during processing can correspond to an increased relaxation rate of the orientation parameter and, therefore, a decrease in anisotropy and material properties after cooling.

High strain actuation liquid crystal elastomers via modulation of mesophase structure

Soft Matter ◽  
2017 ◽  
Vol 13 (41) ◽  
pp. 7537-7547 ◽  
Author(s):  
Mohand O. Saed ◽  
Ross H. Volpe ◽  
Nicholas A. Traugutt ◽  
Rayshan Visvanathan ◽  
Noel A. Clark ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
High Strain ◽  
Stimuli Responsive ◽  
Critical Aspect ◽  
Liquid Crystal Elastomers

Control of the mesophase in liquid crystalline elastomers (LCEs) is a critical aspect in harnessing their unique stimuli-responsive properties.

STRAIN-ORDER COUPLING IN NEMATIC ELASTOMERS: EQUILIBRIUM CONFIGURATIONS

2009 ◽  
Vol 19 (04) ◽  
pp. 601-630 ◽  
Author(s):  
PIERLUIGI CESANA ◽  
ANTONIO DESIMONE
Keyword(s):  
Liquid Crystal ◽  
Boundary Conditions ◽  
Phase Diagrams ◽  
Static Equilibrium ◽  
Explicit Solutions ◽  
Special Boundary ◽  
Equilibrium Solutions ◽  
Nematic Elastomers ◽  
Equilibrium Configurations ◽  
Liquid Crystal Elastomers

We consider models that describe liquid crystal elastomers either in a biaxial or in a uniaxial phase and in the framework of Frank's director theory. We prove the existence of static equilibrium solutions in the presence of frustrations due to electro-mechanical boundary conditions and to applied loads and fields. We find explicit solutions arising in connection with special boundary conditions and the corresponding phase diagrams, leading to significant implications on possible experimental observations.

scholarly journals Electrocaloric and elastocaloric effects in soft materials

2016 ◽  
Vol 374 (2074) ◽  
pp. 20150301 ◽  
Author(s):  
Maja Trček ◽  
Marta Lavrič ◽  
George Cordoyiannis ◽  
Boštjan Zalar ◽  
Brigita Rožič ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
Main Chain ◽  
Soft Materials ◽  
Ion Density ◽  
Caloric Effect ◽  
Direct Measurements ◽  
Cooling Devices ◽  
Composite Mixture ◽  
Liquid Crystal Elastomers

Materials with large caloric effect have the promise of realizing solid-state refrigeration which has potential to be more efficient and environmentally friendly compared with current cooling technologies. Recently, the focus of caloric effects investigations has shifted towards soft materials. An overview of recent direct measurements of the large electrocaloric effect (ECE) in a composite mixture of a liquid crystal and nanoparticles (NPs) and large elastocaloric (eC) effect in main-chain liquid crystal elastomers is given. In mixtures of 12CB liquid crystal with functionalized CdSSe NPs, an ECE exceeding 5 K was found in the vicinity of the isotropic to smectic A phase transition. It is shown that the NPs smear the isotropic to smectic coexistence range in which a large ECE is observed due to latent heat enhancement. NPs acting as traps for ions reduce the moving-ion density and consequently the Joule heating. Direct eC measurements indicate that the significant eC response can be found in main-chain liquid crystalline elastomers, but at a fraction of the stress field in contrast to other eC materials. Both soft materials could play a significant role as active cooling elements or parts of thermal diodes in development of new cooling devices. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.

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