Critical fluctuations and random-anisotropy glass transition in nematic elastomers

Feio, Gabriel; Figueirinhas, J. L.; Tajbakhsh, A. R.; Terentjev, Eugene M.

doi:10.1103/physrevb.78.020201

Cited by 32 publications

(30 citation statements)

References 35 publications

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“…We call this configuration the OG-SG state, since it is the combination of the orbital glass (OG) and spin-nematic glass (SG). The OG-SG states produced by random anisotropy of aerogel strands provide the experimental realization of the random anisotropy glasses discussed in different systems [12], such as random anisotropy Heisenberg spin glasses in magnets [13,14] and nematic glasses in liquid crystals [15,16,17].…”

Section: Theorymentioning

confidence: 99%

Orbital glass and spin glass states of 3He-A in aerogel

et al. 2010

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Glass states of superfluid A-like phase of 3 He in aerogel induced by random orientations of aerogel strands are investigated theoretically and experimentally. In anisotropic aerogel with stretching deformation two glass phases are observed. Both phases represent the anisotropic glass of the orbital ferromagnetic vectorl -the orbital glass (OG). The phases differ by the spin structure: the spin nematic vectord can be either in the ordered spin nematic (SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN) is formed under conventional cooling from normal 3 He. The second phase (OG-SG) is metastable, being obtained by cooling through the superfluid transition temperature, when large enough resonant continuous radio-frequency excitation are applied. NMR signature of different phases allows us to measure the parameter of the global anisotropy of the orbital glass induced by deformation.

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Section: Theorymentioning

confidence: 99%

Orbital glass and spin glass states of 3He-A in aerogel

et al. 2010

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“…Rather, they form polydomain structures with nematic order in local regions, which are macroscopically disordered. These polydomain structures have been seen in many experiments, using a wide range of techniques [3][4][5][6][7]. Indeed, a recent polarized light scattering study shows that liquid-crystal elastomers evolve toward a state of increasing disorder as the isotropicnematic transition proceeds, unless the disorder is suppressed by a gradually increasing load [8].…”

mentioning

confidence: 99%

Dynamic Theory of Polydomain Liquid Crystal Elastomers

Duzgun

Selinger

2015

Phys. Rev. Lett.

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When liquid-crystal elastomers are prepared without any alignment, disordered polydomain structures emerge as the materials are cooled into the nematic phase. These polydomain structures have been attributed to quenched disorder in the cross-linked polymer network. As an alternative explanation, we develop a theory for the dynamics of the isotropic-nematic transition in liquid-crystal elastomers, and show that the dynamics can induce a polydomain structure with a characteristic length scale, through a mechanism analogous to the Cahn-Hilliard equation for phase separation.Liquid-crystal elastomers are remarkable materials that combine the elastic properties of cross-linked polymer networks with the anisotropy of liquid crystals [1]. Any distortion of the polymer network affects the orientational order of the liquid crystal, and any change in the magnitude or direction of liquid-crystal order influences the shape of the polymer network. Hence, these elastomers are useful for applications as actuators or shapechanging materials.For many applications, it is necessary to prepare monodomain liquid-crystal elastomers. In practice, this can be done by applying a mechanical load or other aligning field while crosslinking [2]. Surprisingly, elastomers prepared without an aligning field do not form monodomains. Rather, they form polydomain structures with nematic order in local regions, which are macroscopically disordered. These polydomain structures have been seen in many experiments, using a wide range of techniques [3][4][5][6][7]. Indeed, a recent polarized light scattering study shows that liquid-crystal elastomers evolve toward a state of increasing disorder as the isotropicnematic transition proceeds, unless the disorder is suppressed by a gradually increasing load [8].One important issue in the theory of liquid-crystal elastomers is how to understand the polydomain state. Several theoretical studies have attributed this state to quenched disorder in the polymer network, which can be understood by analogy with spin glass theory [9][10][11][12][13][14][15][16][17]. Effects of quenched disorder have further been modeled and visualized through numerical simulations [18][19][20][21]. More macroscopic theories have shown that the resulting polydomain structure has profound consequences for the material's effective elasticity [22,23].The purpose of this paper is to suggest a different mechanism for the origin of the polydomain state, not related to quenched disorder. We develop a theory for the dynamics of the isotropic-nematic transition in liquidcrystal elastomers, in which growing nematic order is coupled to elastic strain. We explore this theory in two dimensions (2D), using two models for dynamic evolution of nematic order and strain. The theory shows that dynamics can itself select a characteristic length scale for a disordered polydomain structure, through a mechanism similar to the Cahn-Hilliard equation for phase separation. In particular, the theory predicts formation of structures with the form shown in Fig. 1...

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“…DNMR studies [318][319][320] have been done on polysiloxane based main-chain [319] and side-chain [318,320,321] LSCE films, doped with deuterated 8CB-αd 2 , and these were important in characterizing the thermodynamic features of these systems. Also a LCE has been investigated by Feio et al [322] In fact, in common nematogens, the N-I transition between the high temperature I phase and the N phase is first order, but this is not the case for LSCEs. In particular, DNMR experiments were helpful in characterizing the high temperature phase as paranematic (PN) instead of the I phase [318], in analogy with nematic LCs confined in a porous matrix [323].…”

Section: Polymeric Liquid Crystals and Lc Elastomersmentioning

confidence: 97%

Recent NMR Studies of Thermotropic Liquid Crystals

Dong¹

2016

Annual Reports on NMR Spectroscopy

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Critical fluctuations and random-anisotropy glass transition in nematic elastomers

Cited by 32 publications

References 35 publications

Orbital glass and spin glass states of 3He-A in aerogel

Orbital glass and spin glass states of 3He-A in aerogel

Dynamic Theory of Polydomain Liquid Crystal Elastomers

Recent NMR Studies of Thermotropic Liquid Crystals

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