Viscoelasticity of the polydomain-monodomain transition in main-chain liquid crystal elastomers

Azoug, Aurélie; Vasconcellos, V.; Dooling, J.; Saed, Mohand O.; Yakacki, Christopher M.; Nguyen, Thao D.

doi:10.1016/j.polymer.2016.06.022

Cited by 57 publications

(68 citation statements)

References 26 publications

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“…Comparatively, the NG‐PD‐LCE and IG‐PD‐LCE films do not recover their deformation over the 10 min monitored in the experiment, recovering to residual strain values of 37 % and 68 %, respectively. The rate of elastic recovery in polydomain LCEs is known to be limited by the memory of the polymer network . In the IG‐PD‐LCE film, where polymerization occurred prior to LC phase formation, the polymer network has limited elastic memory of the polydomain state.…”

Section: Figurementioning

confidence: 99%

“…The IG‐PD‐LCE film remains deformed for greater than 24 h (Figure S10). Mechanical recovery is improved in the NG‐PD‐LCE material as the memory of the initial polydomain state captured during photopolymerization limits the formation of a single crystal monodomain (lower orientation parameter, polydomain texture still visible under elongation; see Figures S4 and S10), and provides a comparatively larger elastic driving force towards recovery of the initial LC organization . On average, the NG‐PD‐LCE film recovered its deformation in approximately 1 hour (Figure S10).…”

Section: Figurementioning

confidence: 99%

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Mechanotropic Elastomers

et al. 2019

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Liquid crystal elastomers (LCEs) are anisotropic polymeric materials. When subjected to an applied stress, liquid crystalline (LC) mesogens within the elastomeric polymer network (re)orient to the loading direction. The (re)orientation during deformation results in nonlinear stress‐strain dependence (referred to as soft elasticity). Here, we uniquely explore mechanotropic phase transitions in elastomers with appreciable mesogenic content and compare these responses to LCEs in the polydomain orientation. The isotropic (amorphous) elastomers undergo significant directional orientation upon loading, evident in strong birefringence and x‐ray diffraction. Functionally, the mechanotropic displacement of the elastomers to load is also nonlinear. However, unlike the analogous polydomain LCE compositions examined here, the isotropic elastomers rapidly recover after deformation. The mechanotropic orientation of the mesogens in these materials increase the toughness of these thiol‐ene photopolymers by nearly 1300 % relative to a chemically similar elastomer prepared from wholly isotropic precursors.

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Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Mechanotropic Elastomers

et al. 2019

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“…Recently, our group introduced a two‐stage thiol‐acrylate Michael addition‐photopolymerization (TAMAP) methodology for the first time in mesomorphic systems to prepare nematic monodomain main‐chain LCEs . Several recent examples of using TAMAP methodology to prepare main‐chain LCEs have been performed …”

Section: Introductionmentioning

confidence: 99%

Thiol‐acrylate main‐chain liquid‐crystalline elastomers with tunable thermomechanical properties and actuation strain

Saed

Torbati

Starr

et al. 2016

J Polym Sci B Polym Phys

119

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The purpose of this study was to investigate the influence of cross‐linking on the thermomechanical behavior of liquid‐crystalline elastomers (LCEs). Main‐chain LCE networks were synthesized via a thiol‐acrylate Michael addition reaction. The robust nature of this reaction allowed for tailoring of the behavior of the LCEs by varying the concentration and functionality of the cross‐linker. The isotropic rubbery modulus, glass transition temperature, and strain‐to‐failure showed strong dependence on cross‐linker concentration and ranged from 0.9 MPa, 3 °C, and 105% to 3.2 MPa, 25 °C, and 853%, respectively. The isotropic transition temperature (Ti) was shown to be influenced by the functionality of the cross‐linker, ranging from 70 °C to 80 °C for tri‐ and tetra‐functional cross‐linkers. The magnitude of actuation can be tailored by controlling the amount of cross‐linker and applied stress. Actuation increased with increased applied stress and decreased with greater amounts of cross‐linking. The maximum strain actuation achieved was 296% under 100 kPa of bias stress, which resulted in work capacity of 296 kJ/m3 for the lowest cross‐linked networks. Overall, the experimental results provide a fundamental insight linking thermomechanical properties and actuation to a homogenous polydomain nematic LCE networks with order parameters of 0.80 when stretched. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 157–168

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“…Material objectivity is guaranteed by defining strain-energy functions in terms of the scalar invariants. Indeed, by the material frame indifference of W , 5) and by (2.2),…”

Section: An Ideal Liquid Crystal Elastomermentioning

confidence: 99%

A pseudo-anelastic model for stress softening in liquid crystal elastomers

Mihai

Goriely

2020

Proc. R. Soc. A.

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Liquid crystal elastomers exhibit stress softening with residual strain under cyclic loads. Here, we model this phenomenon by generalizing the classical pseudo-elastic formulation of the Mullins effect in rubber. Specifically, we modify the neoclassical strain-energy density of liquid crystal elastomers, depending on the deformation and the nematic director, by incorporating two continuous variables that account for stress softening and the associated set strain. As the material behaviour is governed by different forms of the strain-energy density on loading and unloading, the model is referred to as pseudo-anelastic. We then analyse qualitatively the mechanical responses of the material under cyclic uniaxial tension, which is easier to reproduce in practice, and further specialize the model in order to calibrate its parameters to recent experimental data at different temperatures. The excellent agreement between the numerical and experimental results confirms the suitability of our approach. Since the pseudo-energy function is controlled by the strain-energy density for the primary deformation, it is valid also for materials under multiaxial loads. Our study is relevant to mechanical damping applications and serves as a motivation for further experimental tests.

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Viscoelasticity of the polydomain-monodomain transition in main-chain liquid crystal elastomers

Cited by 57 publications

References 26 publications

Mechanotropic Elastomers

Mechanotropic Elastomers

Thiol‐acrylate main‐chain liquid‐crystalline elastomers with tunable thermomechanical properties and actuation strain

A pseudo-anelastic model for stress softening in liquid crystal elastomers

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