Probing the in-plane liquid-like behavior of liquid crystal elastomers

Tokumoto, Haruki; Zhou, Hao; Takebe, Asaka; Kamitani, Kazutaka; Kojio, Ken; Takahara, Atsushi; Bhattacharya, Kaushik; Urayama, Kenji

doi:10.1126/sciadv.abe9495

Cited by 27 publications

(22 citation statements)

References 46 publications

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“…Finally, the results of the simulations above are in agreement with the observations of Tokumoto et al [71]. This is shown by comparing the stress-stretch relations in Figure 13.…”

Section: Polydomain Materialssupporting

confidence: 90%

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Accelerated computational micromechanics

Zhou,

Bhattacharya

2020

Preprint

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We present an approach to solving problems in micromechanics that is amenable to massively parallel calculations through the use of graphical processing units and other accelerators. The problems lead to nonlinear differential equations that are typically second order in space and first order in time. This combination of nonlinearity and nonlocality makes such problems difficult to solve in parallel. However, this combination is a result of collapsing nonlocal, but linear and universal physical laws (kinematic compatibility, balance laws), and nonlinear but local constitutive relations. We propose an operator-splitting scheme inspired by this structure. The governing equations are formulated as (incremental) variational problems, the differential constraints like compatibility are introduced using an augmented Lagrangian, and the resulting incremental variational principle is solved by the alternating direction method of multipliers. The resulting algorithm has a natural connection to physical principles, and also enables massively parallel implementation on structured grids. We present this method and use it to study two examples. The first concerns the long wavelength instability of finite elasticity, and allows us to verify the approach against previous numerical simulations. We also use this example to study convergence and parallel performance. The second example concerns microstructure evolution in liquid crystal elastomers and provides new insights into some counter-intuitive properties of these materials. We use this example to validate the model and the approach against experimental observations.

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“…Finally, the results of the simulations above are in agreement with the observations of Tokumoto et al [71]. This is shown by comparing the stress-stretch relations in Figure 13.…”

Section: Polydomain Materialssupporting

confidence: 90%

“…Uniaxial and biaxial deformation These simulations are motivated by the experiments reported in Tokumoto et al [71]. They took 65 × 65 × 0.7 mm sheets and subjected them to uniaxial stress and biaxial stretch protocols.…”

Section: Polydomain Materialsmentioning

confidence: 99%

Accelerated computational micromechanics

Zhou,

Bhattacharya

2020

Preprint

Self Cite

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“…This negligible disparity is in contrast to the large shear anisotropy, G 12 » G 13 , reported for a nacre mimetic hybrid stack due to the large rigidity of the inorganic layer 48 . Both ν 31 = ν 32 and ν 12 = ν 21 are typical values of weakly crosslinked elastomer (~0.5) 49 , while ν 31 (=0.46 ± 0.01) is slightly lower compared to the ν 21 (=0.52 ± 0.03) of the isotropic plane ( x 1 , x 2 ); stretching along the x 1 -axis leads to smaller contraction along x 3 -axis than along x 2 -axis 50 . Interestingly, the LCE may be compressible ( ν 13(23) + ν 12(21) < 1) at a normal strain to director n , violating the volume conservation assumption that is normally used for estimation of Poisson’s ratio of LCEs or any rubber materials 38 , 51 .…”

Section: Resultsmentioning

confidence: 87%

“…As already mentioned, the microscopic order parameter, Q = ( r − 1 ) /( r + 2), can be computed from r under the assumption of a freely joined chain 1 . The reported r of the monodomain LCE varies between 2.6 ( Q = 0.35) and 5.5 ( Q = 0.6) 4 , 7 , 50 , 59 . An additional estimate of r (= ) can be directly obtained from the thermally induced contraction, λ T , of LCE along its director in the isotropic state.…”

Section: Resultsmentioning

confidence: 99%

On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies

et al. 2022

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Liquid crystal elastomers that offer exceptional load-deformation response at low frequencies often require consideration of the mechanical anisotropy only along the two symmetry directions. However, emerging applications operating at high frequencies require all five true elastic constants. Here, we utilize Brillouin light spectroscopy to obtain the engineering moduli and probe the strain dependence of the elasticity anisotropy at gigahertz frequencies. The Young’s modulus anisotropy, E||/E⊥~2.6, is unexpectedly lower than that measured by tensile testing, suggesting disparity between the local mesogenic orientation and the larger scale orientation of the network strands. Unprecedented is the robustness of E||/E⊥ to uniaxial load that it does not comply with continuously transformable director orientation observed in the tensile testing. Likewise, the heat conductivity is directional, κ||/κ⊥~3.0 with κ⊥ = 0.16 Wm−1K−1. Conceptually, this work reveals the different length scales involved in the thermoelastic anisotropy and provides insights for programming liquid crystal elastomers on-demand for high-frequency applications.

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“…The maximum value of the DC voltage is limited by the dielectric strength of the elastomer film. In-plane pre-stretching of the elastomer is considered an effective method to increase the dielectric strength [18][19][20] and reduce the thickness of the elastomer film.…”

Section: Dielectric Elastomersmentioning

confidence: 99%

Electroactive Polymer-Based Composites for Artificial Muscle-like Actuators: A Review

et al. 2022

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Unlike traditional actuators, such as piezoelectric ceramic or metallic actuators, polymer actuators are currently attracting more interest in biomedicine due to their unique properties, such as light weight, easy processing, biodegradability, fast response, large active strains, and good mechanical properties. They can be actuated under external stimuli, such as chemical (pH changes), electric, humidity, light, temperature, and magnetic field. Electroactive polymers (EAPs), called ‘artificial muscles’, can be activated by an electric stimulus, and fixed into a temporary shape. Restoring their permanent shape after the release of an electrical field, electroactive polymer is considered the most attractive actuator type because of its high suitability for prosthetics and soft robotics applications. However, robust control, modeling non-linear behavior, and scalable fabrication are considered the most critical challenges for applying the soft robotic systems in real conditions. Researchers from around the world investigate the scientific and engineering foundations of polymer actuators, especially the principles of their work, for the purpose of a better control of their capability and durability. The activation method of actuators and the realization of required mechanical properties are the main restrictions on using actuators in real applications. The latest highlights, operating principles, perspectives, and challenges of electroactive materials (EAPs) such as dielectric EAPs, ferroelectric polymers, electrostrictive graft elastomers, liquid crystal elastomers, ionic gels, and ionic polymer–metal composites are reviewed in this article.

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Probing the in-plane liquid-like behavior of liquid crystal elastomers

Cited by 27 publications

References 46 publications

Accelerated computational micromechanics

Accelerated computational micromechanics

On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies

Electroactive Polymer-Based Composites for Artificial Muscle-like Actuators: A Review

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