1
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Ohzono T, Koyama E. Effects of Operating Mechanical Conditions and Polymer Networks of Nematic Elastomers on Photo-Induced Mechanical Performances. Macromol Rapid Commun 2024:e2300709. [PMID: 38577749 DOI: 10.1002/marc.202300709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 03/21/2024] [Indexed: 04/06/2024]
Abstract
Photoresponsive liquid-crystalline elastomers (LCEs) are promising candidates for light-controlled soft actuators. Photoinduced stress/strain originates from the changes in mechanical properties after light irradiation. However, the correlation between the photoinduced mechanical performance and in-use conditions such as stress/strain states and polymer network properties (such as effective crosslink density and dangling chain density) remains unexplored for practical applications. Here, isometric photo-induced stress or isotonic strain is investigated at different operating strains or stresses, respectively, on LCEs with polymer network variations, produced by different amounts of solvent during polymerization. As the solvent volume increases, the moduli and photoinduced stresses decrease. However, the photo-induced strain, fracture strain, fracture stress, and viscosity increase. The optical response performance initially increases with the operating strain/stress, peaks at a higher actuation strain/stress, and then, decreases depending on the polymer network. The maximum work densities, which also depend on the operating stress, are in the range of ≈200-300 kJm-3. These findings, highlighting the significant variations in the mechanical performance with the operating stress/strain ranges and amount of solvent used in the synthesis, are critical for designing LCE-based mechanical devices.
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Affiliation(s)
- Takuya Ohzono
- Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565, Japan
| | - Emiko Koyama
- Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565, Japan
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2
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Barnes M, Feng F, Biggins JS. Surface Instability in a Nematic Elastomer. PHYSICAL REVIEW LETTERS 2023; 131:238101. [PMID: 38134776 DOI: 10.1103/physrevlett.131.238101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 11/03/2023] [Indexed: 12/24/2023]
Abstract
Liquid crystal elastomers (LCEs) are soft phase-changing solids that exhibit large reversible contractions upon heating, Goldstone-like soft modes, and resultant microstructural instabilities. We heat a planar LCE slab to isotropic, clamp the lower surface, then cool back to nematic. Clamping prevents macroscopic elongation, producing compression and microstructure. We see that the free surface destabilizes, adopting topography with amplitude and wavelength similar to thickness. To understand the instability, we numerically compute the microstructural relaxation of a "nonideal" LCE energy. Linear stability reveals a Biot-like scale-free instability, but with oblique wave vector. However, simulation and experiment show that, unlike classic elastic creasing, instability culminates in a crosshatch without cusps or hysteresis, and is constructed entirely from low-stress soft modes.
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Affiliation(s)
- Morgan Barnes
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom
| | - Fan Feng
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom
| | - John S Biggins
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom
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3
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Park S, Oh Y, Moon J, Chung H. Recent Trends in Continuum Modeling of Liquid Crystal Networks: A Mini-Review. Polymers (Basel) 2023; 15:polym15081904. [PMID: 37112051 PMCID: PMC10142630 DOI: 10.3390/polym15081904] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 04/10/2023] [Accepted: 04/12/2023] [Indexed: 04/29/2023] Open
Abstract
This work aims to provide a comprehensive review of the continuum models of the phase behaviors of liquid crystal networks (LCNs), novel materials with various engineering applications thanks to their unique composition of polymer and liquid crystal. Two distinct behaviors are primarily considered: soft elasticity and spontaneous deformation found in the material. First, we revisit these characteristic phase behaviors, followed by an introduction of various constitutive models with diverse techniques and fidelities in describing the phase behaviors. We also present finite element models that predict these behaviors, emphasizing the importance of such models in predicting the material's behavior. By disseminating various models essential to understanding the underlying physics of the behavior, we hope to help researchers and engineers harness the material's full potential. Finally, we discuss future research directions necessary to advance our understanding of LCNs further and enable more sophisticated and precise control of their properties. Overall, this review provides a comprehensive understanding of the state-of-the-art techniques and models used to analyze the behavior of LCNs and their potential for various engineering applications.
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Affiliation(s)
- Sanghyeon Park
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Youngtaek Oh
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Jeseung Moon
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Hayoung Chung
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
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4
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Feng F, Duffy D, Warner M, Biggins JS. Interfacial metric mechanics: stitching patterns of shape change in active sheets. Proc Math Phys Eng Sci 2022; 478:20220230. [PMID: 35814332 PMCID: PMC9240917 DOI: 10.1098/rspa.2022.0230] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 06/09/2022] [Indexed: 11/22/2022] Open
Abstract
A flat sheet programmed with a planar pattern of spontaneous shape change will morph into a curved surface. Such metric mechanics is seen in growing biological sheets, and may be engineered in actuating soft matter sheets such as phase-changing liquid crystal elastomers (LCEs), swelling gels and inflating baromorphs. Here, we show how to combine multiple patterns in a sheet by stitching regions of different shape changes together piecewise along interfaces. This approach allows simple patterns to be used as building blocks, and enables the design of multi-material or active/passive sheets. We give a general condition for an interface to be geometrically compatible, and explore its consequences for LCE/LCE, gel/gel and active/passive interfaces. In contraction/elongation systems such as LCEs, we find an infinite set of compatible interfaces between any pair of patterns along which the metric is discontinuous, and a finite number across which the metric is continuous. As an example, we find all possible interfaces between pairs of LCE logarithmic spiral patterns. By contrast, in isotropic systems such as swelling gels, only a finite number of continuous interfaces are available, greatly limiting the potential of stitching. In both continuous and discontinuous cases, we find the stitched interfaces generically carry singular Gaussian curvature, leading to intrinsically curved folds in the actuated surface. We give a general expression for the distribution of this curvature, and a more specialized form for interfaces in LCE patterns. The interfaces thus also have rich geometric and mechanical properties in their own right.
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Affiliation(s)
- Fan Feng
- Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
| | - Daniel Duffy
- Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
| | - Mark Warner
- Department of Physics, University of Cambridge, Cambridge CB3 0HE, UK
| | - John S. Biggins
- Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
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5
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Light-Activated Elongation/Shortening and Twisting of a Nematic Elastomer Balloon. Polymers (Basel) 2022; 14:polym14061249. [PMID: 35335579 PMCID: PMC8953924 DOI: 10.3390/polym14061249] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Revised: 03/15/2022] [Accepted: 03/17/2022] [Indexed: 02/04/2023] Open
Abstract
Nematic elastomer balloons with inflation-induced axial contraction and shear/torsion effect can be used as actuators for soft robots, artificial muscles, and biomedical instruments. The nematic elastomer can also generate drastic shape changes under illumination, and thus light can be utilized to activate the deformation of nematic elastomer balloons with huge advantages of being accurate, fast, untethered, and environmentally sustainable without chemical byproducts. To explore light-activated deformation behaviors of the balloon, a phenomenological relationship between light intensity and material parameters describing polymer backbone anisotropy is proposed from experiments, and a theoretical model of an optically-responsive nematic elastomer balloon is established based on the nematic elastomer theory. Various light-activated elongation/shortening and twisting behaviors in the cases of free-standing and axial-loading are presented and their mechanisms are elucidated. The light intensity and initial mesogen angle have great influences on the light-activated deformations including the radius, length, shearing angle and mesogen angle. Light can be easily controlled to trigger rich deformation processes, including elongation/shortening and torsion. The results of this paper are expected to promote the understanding of the light-activated deformation behaviors of the nematic elastomer balloon, and the applications in light-activated actuators and machines.
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6
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Mihai LA, Wang H, Guilleminot J, Goriely A. Nematic liquid crystalline elastomers are aeolotropic materials. Proc Math Phys Eng Sci 2021; 477:20210259. [PMID: 35153581 PMCID: PMC8424302 DOI: 10.1098/rspa.2021.0259] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 08/04/2021] [Indexed: 11/12/2022] Open
Abstract
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.
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Affiliation(s)
- L Angela Mihai
- School of Mathematics, Cardiff University, Senghennydd Road, Cardiff CF24 4AG, UK
| | - Haoran Wang
- Department of Mechanical and Aerospace Engineering,Utah State University, Logan, UT 84322-4130, USA
| | - Johann Guilleminot
- Department of Civil and Environmental Engineering, Duke University, Durham, NC 27708-0287, USA
| | - Alain Goriely
- Mathematical Institute, University of Oxford, Woodstock Road, Oxford OX2 6GG, UK
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7
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Tokumoto H, Zhou H, Takebe A, Kamitani K, Kojio K, Takahara A, Bhattacharya K, Urayama K. Probing the in-plane liquid-like behavior of liquid crystal elastomers. SCIENCE ADVANCES 2021; 7:eabe9495. [PMID: 34144981 PMCID: PMC8213220 DOI: 10.1126/sciadv.abe9495] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Accepted: 05/05/2021] [Indexed: 06/12/2023]
Abstract
When isotropic solids are unequally stretched in two orthogonal directions, the true stress (force per actual cross-sectional area) in the larger strain direction is typically higher than that in the smaller one. We show that thiol-acrylate liquid crystal elastomers with polydomain texture exhibit an unusual tendency: The true stresses in the two directions are always identical and governed only by the area change in the loading plane, independently of the combination of imposed strains in the two directions. This feature proves a previously unidentified state of matter that can vary its shape freely with no extra mechanical energy like liquids when deformed in the plane. The theory and simulation that explain the unique behavior are also provided. The in-plane liquid-like behavior opens doors for manifold applications, including wrinkle-free membranes and adaptable materials.
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Affiliation(s)
- Haruki Tokumoto
- Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585, Japan
| | - Hao Zhou
- Department of Mechanical and Civil Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Asaka Takebe
- Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585, Japan
| | - Kazutaka Kamitani
- Institute for Materials Chemistry and Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
| | - Ken Kojio
- Institute for Materials Chemistry and Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
| | - Atsushi Takahara
- Institute for Materials Chemistry and Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
| | - Kaushik Bhattacharya
- Department of Mechanical and Civil Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
| | - Kenji Urayama
- Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585, Japan.
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8
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Okamoto S, Sakurai S, Urayama K. Effect of stretching angle on the stress plateau behavior of main-chain liquid crystal elastomers. SOFT MATTER 2021; 17:3128-3136. [PMID: 33599677 DOI: 10.1039/d0sm02244f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The equilibrium nonlinear stress-stretch relationships for a monodomain main-chain nematic elastomer (MNE) are investigated by varying the angle between the stretching and initial director axes (θ0). Angle θ0 has pronounced effects on the ultimate elongation as well as on the width of the low stress plateau regime (Λp) during director rotation, whereas θ0 has no appreciable effect on the plateau stress (σp). In the stretching normal to the initial director (θ0 = 90°), the plateau end exceeds 200% strain. At oblique angles of 90° > θ0≥ 35°, Λp decreases with decreasing θ0, whereas the definite plateau regime vanishes at θ0 < 24°. Wide-angle X-ray scattering and polarized optical microscopy measurements reveal that the director rotates uniformly in the biased direction for the MNE of θ0°≪ 90°, whereas directors rotating clockwise and counterclockwise are coexistent for θ0 = 90°. Over the entire plateau regime, the MNEs exhibit pure shear deformation characterized by a Poisson's ratio of zero in the direction of the rotation axis. The Λp for the corresponding polydomain NE (PNE) undergoing a transition to the monodomain alignment is smaller than that of the MNE of θ0 = 90°, while the σp values for both NEs are almost similar. The semi-soft elasticity concept satisfactorily explains the effects of θ0 on Λp, and the Λp value of the PNE, using a single anisotropy parameter which is evaluated from the degree of thermally induced deformation of MNEs.
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Affiliation(s)
- Suzuka Okamoto
- Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585, Japan.
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9
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Ohzono T, Katoh K, Minamikawa H, Saed MO, Terentjev EM. Internal constraints and arrested relaxation in main-chain nematic elastomers. Nat Commun 2021; 12:787. [PMID: 33542238 PMCID: PMC7862651 DOI: 10.1038/s41467-021-21036-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 01/04/2021] [Indexed: 11/16/2022] Open
Abstract
Nematic 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.
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Affiliation(s)
- Takuya Ohzono
- Research Institute for Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
| | - Kaoru Katoh
- Biomedical Research Institute, AIST, Tsukuba, Japan
| | | | - Mohand O Saed
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
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10
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Nguyen TS, Selinger JV. Theory of liquid crystal elastomers and polymer networks : Connection between neoclassical theory and differential geometry. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2017; 40:76. [PMID: 28913812 DOI: 10.1140/epje/i2017-11569-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2017] [Accepted: 09/06/2017] [Indexed: 06/07/2023]
Abstract
In liquid crystal elastomers and polymer networks, the orientational order of liquid crystals is coupled with elastic distortions of crosslinked polymers. Previous theoretical research has described these materials through two different approaches: a neoclassical theory based on the liquid crystal director and the deformation gradient tensor, and a geometric elasticity theory based on the difference between the actual metric tensor and a reference metric. Here, we connect those two approaches using a formalism based on differential geometry. Through this connection, we determine how both the director and the geometry respond to a change of temperature.
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Affiliation(s)
- Thanh-Son Nguyen
- Liquid Crystal Institute, Kent State University, 44242, Kent, OH, USA
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11
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Chung H, Choi J, Yun JH, Cho M. Nonlinear photomechanics of nematic networks: upscaling microscopic behaviour to macroscopic deformation. Sci Rep 2016; 6:20026. [PMID: 26828417 PMCID: PMC4734330 DOI: 10.1038/srep20026] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 12/08/2015] [Indexed: 11/29/2022] Open
Abstract
A liquid crystal network whose chromophores are functionalized by photochromic dye exhibits light-induced mechanical behaviour. As a result, the micro-scaled thermotropic traits of the network and the macroscopic phase behaviour are both influenced as light alternates the shape of the dyes. In this paper, we present an analysis of this photomechanical behaviour based on the proposed multiscale framework, which incorporates the molecular details of microstate evolution into a continuum-based understanding. The effects of trans-to-cis photoisomerization driven by actinic light irradiation are first examined using molecular dynamics simulations, and are compared against the predictions of the classical dilution model; this reveals certain characteristics of mesogenic interaction upon isomerization, followed by changes in the polymeric structure. We then upscale the thermotropic phase-related information with the aid of a nonlinear finite element analysis; macroscopic deflection with respect to the wide ranges of temperature and actinic light intensity are thereby examined, which reveals that the classical model underestimates the true deformation. This work therefore provides measures for analysing photomechanics in general by bridging the gap between the micro- and macro-scales.
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Affiliation(s)
- Hayoung Chung
- School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, 151-744, South Korea
| | - Joonmyung Choi
- School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, 151-744, South Korea
| | - Jung-Hoon Yun
- School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, 151-744, South Korea
| | - Maenghyo Cho
- School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, 151-744, South Korea
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12
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Diaz Calleja R, Díaz-Boïls P, Llovera-Segovia P, Quijano A. On the nonlinear behaviour of nematic single crystal elastomers under biaxial mechanic and electrical force fields. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2014; 37:22. [PMID: 25080174 DOI: 10.1140/epje/i2014-14066-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Accepted: 06/25/2014] [Indexed: 06/03/2023]
Abstract
A slab of nematic-side-chain-liquid-single-crystal elastomer (NSCLSCE), with the director initially oriented in the z -direction, is subjected to a pair of equal mechanical loads and electrical force fields in the x , y directions. The electric fields tend to make easier the rotation of the director after the application of the mechanical force field. A nonlinear expression for the free energy density is used to obtain the interval of stretching for which the system becomes unstable. However, the elastic energy of the network is assumed to be linear. The stress-strain curves predicted by the model show an unstable zone between two linearly increasing segments. The possibility of bifurcation phenomena has been examined.
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Affiliation(s)
- Ricardo Diaz Calleja
- ITE, Universitat Politècnica de València, Camino de Vera s/n, E-46022, Valencia, Spain,
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13
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Liarte DB. Tricritical behavior of soft nematic elastomers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:062144. [PMID: 24483422 DOI: 10.1103/physreve.88.062144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Indexed: 06/03/2023]
Abstract
We propose a lattice statistical model to investigate the phase diagrams and the soft responses of nematic liquid-crystal elastomers. Using suitably scaled infinite-range interactions, we obtain exact self-consistent equations for the tensor components of the nematic order parameter in terms of temperature, the distortion and stress tensors, and the initial nematic order. These equations are amenable to simple numerical calculations, which are used to characterize the low-temperature soft regime. We find a peculiar phase diagram, in terms of temperature and the diagonal component of the distortion tensor along the stretching direction, with first- and second-order transitions to the soft phase, and the prediction of tricritical points. This behavior is not qualitatively changed if we use different values of the initial nematic order parameter.
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Affiliation(s)
- Danilo B Liarte
- Laboratory of Atomic and Solid State Physics, Clark Hall, Cornell University, Ithaca, New York 14853-2501, USA and Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, CEP 05314-970, São Paulo, São Paulo, Brazil
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14
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Köpf MH, Pismen LM. Phase separation and disorder in doped nematic elastomers. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2013; 36:121. [PMID: 24158266 DOI: 10.1140/epje/i2013-13121-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/23/2013] [Accepted: 09/30/2013] [Indexed: 06/02/2023]
Abstract
We formulate and analyse a model describing the combined effect of mechanical deformation, dynamics of the nematic order parameter, and concentration inhomogeneities in an elastomeric mixture of a mesogenic and an isotropic component. The uniform nematic state may exhibit a long-wave instability corresponding to nematic-isotropic demixing. Numerical simulations starting from either a perfectly ordered nematic state or a quenched isotropic state show that coupling between the mesogen concentration and the nematic order parameter influences the shape and orientation of the domains formed during the demixing process.
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Affiliation(s)
- M H Köpf
- Department of Chemical Engineering, Technion - Israel Institute of Technology, 32000, Haifa, Israel
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15
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Brown AW, Adams JM. Numerical study of stretched smectic-A elastomer sheets. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:012512. [PMID: 23944479 DOI: 10.1103/physreve.88.012512] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Indexed: 06/02/2023]
Abstract
We present a numerical study of stretching monodomain smectic-A elastomer sheets, computed using the finite element method. When stretched parallel to their smectic layer normal the smectic layers are unstable to a transition to a buckled state. We model macroscopic deformations by replacing the microscopic energy with a coarse grained effective free energy that accounts for the fine-scale layer buckling. We augment this model with a term to describe the energy of deforming buckled layers, which is necessary to reproduce the experimentally observed Poisson ratios postbuckling. We examine the spatial distribution of the microstructure phases for various stretching angles relative to the layer normal and for different length-to-width aspect ratios. When stretching parallel to the layer normal the majority of the sample forms a bidirectionally buckled microstructure, except at the clamps where a unidirectionally buckled microstructure is predicted. When stretching at small inclinations to the layer normal the phase of the sample is sensitive to the aspect ratio of the sample, with the bidirectionally buckled phase persistent to large angles only for small aspect ratios. We relate these theoretical results to experiments on smectic-A elastomers.
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Affiliation(s)
- A W Brown
- SEPnet and the Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, GU2 7XH, United Kingdom
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16
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Molecular simulations elucidate electric field actuation in swollen liquid crystal elastomers. Proc Natl Acad Sci U S A 2012; 109:10193-8. [PMID: 22679288 DOI: 10.1073/pnas.1121235109] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Swollen elastomer liquid crystals undergo significant deformations by application of an electric field perpendicular to their alignment axis, as shown in experiments by Urayama et al. [Urayama K, Honda S, Takigawa T (2006) Macromolecules 39:1943-1949]. Here we clarify this surprising effect at the molecular level using large-scale Monte Carlo simulations of an off-lattice model based on a soft Gay-Berne potential. We provide the internal change of molecular organization, as well as the key observables during the actuation cycle.
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17
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Domenici V. 2H NMR studies of liquid crystal elastomers: macroscopic vs. molecular properties. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 63:1-32. [PMID: 22546343 DOI: 10.1016/j.pnmrs.2011.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/27/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy.
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18
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Brown AW, Adams JM. Negative Poisson's ratio and semisoft elasticity of smectic-C liquid-crystal elastomers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:011703. [PMID: 22400579 DOI: 10.1103/physreve.85.011703] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Revised: 12/09/2011] [Indexed: 05/31/2023]
Abstract
Models of smectic-C liquid-crystal elastomers predict that they can display soft elasticity, in which the shape of the elastomer changes at no energy cost. The amplitude of the soft mode and the accompanying shears are dependent on the orientation of the layer normal and the director with respect to the stretch axis. We demonstrate that in some geometries the director is forced to rotate perpendicular to the stretch axis, causing lateral expansion of the sample-a negative Poisson's ratio. Current models do not include the effect of imperfections that must be present in the physical sample. We investigate the effect of a simple model of these imperfections on the soft modes in monodomain smectic-C elastomers in a variety of geometries. When stretching parallel to the layer normal (with imposed strain) the elastomer has a negative stiffness once the director starts to rotate. We show that this is a result of the negative Poisson's ratio in this geometry through a simple scalar model.
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Affiliation(s)
- A W Brown
- SEPnet and the Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom
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19
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Rogez D, Martinoty P. Mechanical properties of monodomain nematic side-chain liquid-crystalline elastomers with homeotropic and in-plane orientation of the director. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2011; 34:69. [PMID: 21755436 DOI: 10.1140/epje/i2011-11069-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 04/02/2011] [Accepted: 06/22/2011] [Indexed: 05/31/2023]
Abstract
We present the first study of the shear mechanical properties of monodomain nematic side-chain liquid-crystal elastomers (SCLCEs) prepared by cross-linking with UV irradiation a nematic side-chain liquid-crystal polymer oriented with an electric or a magnetic field. Their elastic behavior was studied in the dry, swollen and stretched states, in order to check the various theoretical descriptions of these systems. The shear measurements taken on the dry samples show that the shear anisotropy is much smaller than that of the usual twice cross-linked samples oriented by a mechanical stretching of the network formed after the first cross-linking step, demonstrating that the elasticity of the networks strongly depends on the preparation procedure used. The shear experiments performed on the swollen state of these two different types of elastomers reveal that the elasticity of the network is Gaussian for the elastomers oriented with the electric or the magnetic field, and non-Gaussian for the elastomers oriented with the usual stretching procedure. The analysis of the stress-strain curves of both types of elastomers with the neoclassical model based on Gaussian rubber elasticity confirms the Gaussian and non-Gaussian nature of their elasticity. The shear experiments performed as a function of the elongation of the homeotropically oriented elastomer when the shear is applied in a direction parallel to the elongation, do not show the decrease of the associated shear modulus, which is theoretically expected when the strain approaches the threshold value marking the beginning of the elastic plateau. However, the observation of this effect could be prevented by possible small misalignments of the director, as suggested by a calculation presented in one of the theories describing this effect.
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Affiliation(s)
- D Rogez
- UPR 22, CNRS/UDS, Institut Charles Sadron, 23 rue du Loess, 67034 Strasbourg, France
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20
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Mbanga BL, Ye F, Selinger JV, Selinger RLB. Modeling elastic instabilities in nematic elastomers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:051701. [PMID: 21230488 DOI: 10.1103/physreve.82.051701] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Revised: 07/25/2010] [Indexed: 05/30/2023]
Abstract
Liquid crystal elastomers are cross-linked polymer networks covalently bonded with liquid crystal mesogens. In the nematic phase, due to strong coupling between mechanical strain and orientational order, these materials display strain-induced instabilities associated with formation and evolution of orientational domains. Using a three-dimensional finite element elastodynamics simulation, we investigate one such instability, the onset of stripe formation in a monodomain film stretched along an axis perpendicular to the nematic director. In our simulation, we observe the formation of striped domains with alternating director rotation. This model allows us to explore the fundamental physics governing dynamic mechanical response of nematic elastomers and also provides a potentially useful computational tool for engineering device applications.
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Affiliation(s)
- Badel L Mbanga
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
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21
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Lubensky TC, Ye F. Elastic response and Ward identities in stressed nematic elastomers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:011704. [PMID: 20866632 DOI: 10.1103/physreve.82.011704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2010] [Indexed: 05/29/2023]
Abstract
Nematic elastomers exhibit a rich elastic response to external stresses. Of particular interest is the semisoft response of elastomers with an anisotropy direction (z) frozen in by a double cross-linking process. This response is characterized by a stress-strain curve for stresses along x perpendicular to z that rises initially, exhibits a nearly flat plateau between two critical values of strain, and then rises again. This paper explores elastic response in semisoft elastomers as a function of externally applied strain. It derives general Ward identities for elastic moduli and shows that the elastic modulus measuring response to xz shears vanishes at the boundaries of the semisoft plateau whereas moduli measuring response to shears perpendicular to the xz plane do not. It then calculates all relevant moduli in a simple model of elastomers and verifies the general Ward-identity predictions.
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Affiliation(s)
- T C Lubensky
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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22
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Petelin A, Copic M. Observation of a soft mode of elastic instability in liquid crystal elastomers. PHYSICAL REVIEW LETTERS 2009; 103:077801. [PMID: 19792688 DOI: 10.1103/physrevlett.103.077801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Indexed: 05/28/2023]
Abstract
In monodomain liquid crystal elastomers a symmetry-breaking locked-in anisotropy causes a semisoft elastic response characterized by a plateau in the stress-strain curve. We show by dynamic light scattering performed as a function of deformation that the relaxation rate of the nematic director fluctuations decreases with strain to a very small value at the onset of the soft elastic response, revealing the existence of a dynamic soft mode. The results are in complete agreement with the theory of semisoft elasticity and allow us to determine all the constants of the model.
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Affiliation(s)
- Andrej Petelin
- Jozef Stefan Institute, Jamova 39, Ljubljana SI-1000, Slovenia
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23
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Adams JM, Warner M. Mechanical switching of ferroelectric rubber. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:061704. [PMID: 19658513 DOI: 10.1103/physreve.79.061704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2006] [Revised: 03/19/2009] [Indexed: 05/28/2023]
Abstract
At the A to C transition, smectic elastomers have recently been observed to undergo approximately 35% spontaneous shear strains. We first explicitly describe how strains of up to twice this value could be mechanically or electrically induced in Sm-C elastomers by rotation of the director on a cone around the layer normal with an elastic cost dependent on constraints. Second, for typical sample geometries, we give the various microstructures in Sm-C akin to those seen in nematic elastomers under distortions with constraints. It is possible to give explicit results for the nature of the textures. Chiral Sm-C elastomers are ferroelectric. We calculate how the polarization could be mechanically reversed by large, hard, or soft strains of the rubber depending upon sample geometry.
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Affiliation(s)
- J M Adams
- Department of Physics, University of Surrey, Surrey GU2 7XH, United Kingdom
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24
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Biggins J. Strain-induced polarization in non-ideal chiral nematic elastomers. Proc Math Phys Eng Sci 2009. [DOI: 10.1098/rspa.2008.0452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Symmetry arguments are advanced that, although ideal chiral nematic elastomers cannot show strain-induced electrical polarization, non-ideal ones can. Phenomenological arguments are then presented, which predict a simple and universal form for the direction and strain dependence of the polarization. A microscopic minimal model is also developed, which predicts the same form. Finally, an example of a polarization–strain curve is calculated for a typical experimental geometry. In this geometry, the polarization is exactly zero at both small and large strains, but pronounced for a large set of intermediate strains corresponding to the strains that cause incremental rotation of the nematic director.
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Affiliation(s)
- J.S. Biggins
- Cavendish Laboratory, University of CambridgeMadingley Road, Cambridge CB3 0HE, UK
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25
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Affiliation(s)
- Fangfu Ye
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - T. C. Lubensky
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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26
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Fukunaga A, Urayama K, Takigawa T, DeSimone A, Teresi L. Dynamics of Electro-Opto-Mechanical Effects in Swollen Nematic Elastomers. Macromolecules 2008. [DOI: 10.1021/ma801639j] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Atsushi Fukunaga
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan, SISSA-International School for Advanced Studies, I-34014 Trieste, Italy, and SMFM, Università Roma Tre, I-00146 Rome, Italy
| | - Kenji Urayama
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan, SISSA-International School for Advanced Studies, I-34014 Trieste, Italy, and SMFM, Università Roma Tre, I-00146 Rome, Italy
| | - Toshikazu Takigawa
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan, SISSA-International School for Advanced Studies, I-34014 Trieste, Italy, and SMFM, Università Roma Tre, I-00146 Rome, Italy
| | - Antonio DeSimone
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan, SISSA-International School for Advanced Studies, I-34014 Trieste, Italy, and SMFM, Università Roma Tre, I-00146 Rome, Italy
| | - Luciano Teresi
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan, SISSA-International School for Advanced Studies, I-34014 Trieste, Italy, and SMFM, Università Roma Tre, I-00146 Rome, Italy
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27
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Biggins JS, Terentjev EM, Warner M. Semisoft elastic response of nematic elastomers to complex deformations. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:041704. [PMID: 18999442 DOI: 10.1103/physreve.78.041704] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2008] [Indexed: 05/27/2023]
Abstract
We consider a relaxed semisoft elastomer with its director oriented along the z axis that is first subjected to a large stretch in the x direction then to a slight x-z shear. We give a general argument that in any theory including director rotation, at the onset and end of the director rotation induced by these large stretches, there will be kinks in the stress-large strain curve (forming a stress-strain plateau) and zeros in the x-z shear modulus (C5) associated with small shears imposed on top of the stretches. We then find the analytical forms of the C5 -strain curves for a particular model of semisoftness (arising from compositional fluctuations) and show that it, together with the known stress-strain curve, provides the basis for a strong test of this theory. Finally, we consider the scope for other semisoft models and show that the compositional fluctuations model in fact yielded a generic form, that is, it is the most general quadratic free energy that does not explicitly include a final state direction other than the director. By introducing such additional directions, a large range of alternative models could be developed.
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Affiliation(s)
- J S Biggins
- Cavendish Laboratory, Madingley Road, Cambridge, CB3 0HE, United Kingdom
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28
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Fortunelli A, Ortiz M. Constitutive model for plasticity in an amorphous polycarbonate. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:041806. [PMID: 17995018 DOI: 10.1103/physreve.76.041806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2007] [Indexed: 05/25/2023]
Abstract
A constitutive model for describing the mechanical response of an amorphous glassy polycarbonate is proposed. The model is based on an isotropic elastic phase surrounded by an SO(3) continuum of plastic phases onto which the elastic phase can collapse under strain. An approximate relaxed energy is developed for this model on the basis of physical considerations and extensive numerical testing, and it is shown that it corresponds to an ideal elastic-plastic behavior. Kinetic effects are introduced as rate-independent viscoplasticity, and a comparison with experimental data is presented, showing that the proposed model is able to capture the main features of the plastic behavior of amophous glassy polycarbonate.
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Affiliation(s)
- A Fortunelli
- Molecular Modeling Laboratory, Istituto per i Processi Chimico-Fisici del C.N.R., v. G. Moruzzi, 1-56124, Pisa, Italy
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29
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Urayama K, Mashita R, Kobayashi I, Takigawa T. Stretching-Induced Director Rotation in Thin Films of Liquid Crystal Elastomers with Homeotropic Alignment. Macromolecules 2007. [DOI: 10.1021/ma071104y] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Kenji Urayama
- Department of Materials Chemistry, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan, and Electronic Materials Research Laboratories, Nissan Chemical Industries, Funabashi, Chiba 273-0000, Japan
| | - Ryo Mashita
- Department of Materials Chemistry, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan, and Electronic Materials Research Laboratories, Nissan Chemical Industries, Funabashi, Chiba 273-0000, Japan
| | - Ichiro Kobayashi
- Department of Materials Chemistry, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan, and Electronic Materials Research Laboratories, Nissan Chemical Industries, Funabashi, Chiba 273-0000, Japan
| | - Toshikazu Takigawa
- Department of Materials Chemistry, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan, and Electronic Materials Research Laboratories, Nissan Chemical Industries, Funabashi, Chiba 273-0000, Japan
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30
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Ye F, Mukhopadhyay R, Stenull O, Lubensky TC. Semisoft nematic elastomers and nematics in crossed electric and magnetic fields. PHYSICAL REVIEW LETTERS 2007; 98:147801. [PMID: 17501313 DOI: 10.1103/physrevlett.98.147801] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Indexed: 05/15/2023]
Abstract
Nematic elastomers with a locked-in anisotropy direction exhibit semisoft elastic response characterized by a plateau in the stress-strain curve in which stress does not change with strain. We calculate the global phase diagram for a minimal model, which is equivalent to one describing a nematic in crossed electric and magnetic fields, and show that semisoft behavior is associated with a broken symmetry biaxial phase and that it persists well into the supercritical regime. We also consider generalizations beyond the minimal model and find similar results.
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Affiliation(s)
- Fangfu Ye
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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31
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Urayama K, Honda S, Takigawa T. Deformation Coupled to Director Rotation in Swollen Nematic Elastomers under Electric Fields. Macromolecules 2006. [DOI: 10.1021/ma052762q] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kenji Urayama
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan
| | - Seiji Honda
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan
| | - Toshikazu Takigawa
- Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan
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32
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Li J, Tammer M, Kremer F, Komp A, Finkelmann H. Strain-induced reorientation and mobility in nematic liquid-crystalline elastomers as studied by time-resolved FTIR spectroscopy. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2005; 17:423-8. [PMID: 16044200 DOI: 10.1140/epje/i2005-10018-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2005] [Accepted: 05/29/2005] [Indexed: 05/03/2023]
Abstract
Polarized Fourier transform infrared (FTIR) spectroscopy is employed to study the segmental orientation and mobility of liquid-crystalline elastomers (LCEs) with a monodomain structure in response to external mechanical fields parallel and perpendicular to the initial nematic director. The mean orientation and the molecular order parameter of the different molecular moieties referring to the mesogen, the spacer and the network are analyzed in detail. Parallel stretch leaves the mean orientation of the different molecular moieties and its molecular order parameter nearly uninfluenced. Perpendicular stretch results in a threshold-like dependence: for elongation ratios lambda < or = lambda(c) = 1.3 (10 mol% crosslinker density), respectively lambda < or = lambda(c) = 1.6 (5 mol% crosslinker density) no change of the mean orientation and the molecular order parameters is observed, while for lambda > or = lambda(c) all molecular units reorient and their molecular order parameters are strongly decreased. The present studies give no indications that the reorientational dynamics of the network and the mesogens differ as long as the elongation ratio is smaller than lambda(c).
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Affiliation(s)
- J Li
- Institute of Experimental Physics I, University of Leipzig, Linnéstrasse 5, Leipzig, Germany.
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33
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Lebar A, Kutnjak Z, Zumer S, Finkelmann H, Sánchez-Ferrer A, Zalar B. Evidence of supercritical behavior in liquid single crystal elastomers. PHYSICAL REVIEW LETTERS 2005; 94:197801. [PMID: 16090213 DOI: 10.1103/physrevlett.94.197801] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Indexed: 05/03/2023]
Abstract
Temperature profiles of the first and the second moment of the nematic order parameter distribution function, as determined from the deuteron nuclear magnetic resonance line shapes, as well as heat capacity response, provide support for the supercritical scenario of the nematic-paranematic phase transition in liquid single crystal elastomers. The relative strength of the locked-in internal mechanical field with respect to the critical field can be decreased by swelling the elastomer samples with low molecular mass nematogen. By increasing the concentration of the dopant, critical and below-critical behavior is promoted.
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Affiliation(s)
- A Lebar
- J. Stefan Institute, Ljubljana, Slovenia
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34
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Tammer M, Li J, Komp A, Finkelmann H, Kremer F. FTIR-Spectroscopy on Segmental Reorientation of a Nematic Elastomer under External Mechanical Fields. MACROMOL CHEM PHYS 2005. [DOI: 10.1002/macp.200500050] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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