Criticality Controlled by Cross-Linking Density in Liquid Single-Crystal Elastomers

Cordoyiannis, George; Lebar, Andrija; Zalar, Boštjan; Žumer, S.; Finkelmann, Heino; Kutnjak, Zdravko

doi:10.1103/physrevlett.99.197801

Cited by 40 publications

(62 citation statements)

References 18 publications

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“…is a necessary feature of a first-order transition and which has been observed in previous NMR experiments on nematic elastomers [20,21] (which, for various reasons, always had a local stress frozen into the network preventing critical fluctuations).…”

Section: Deuterium Nmr Analysismentioning

confidence: 84%

“…It is well-known that monodomain (macroscopically aligned, crosslinked under uniaxial external field) nematic elastomers have a diffuse supercritical transition, with its sharpness decreasing with more rigid crosslinkers or higher external fields imposed at formation. The recent detailed calorimetric study [21] gives the details of this, and the earlier literature. There are very few studies of polydomain systems, and none that examine the soft un-entangled networks (obtain by de-swelling, with small flexible crosslinks).…”

Section: Nematic-isotropic Transitionmentioning

confidence: 99%

“…The alignment in these materials can be installed in two ways: (1) by applying a uniaxial field (usually mechanical stress) to an original polydomain texture and passing through the polydomain-monodomain transition [12,17], or (2) by crosslinking the network in a state uniformly aligned by a mechanical, electric, or surface field [18,19]. In both cases, of course, one does not expect a true phase transition and indeed all the reports find the varying degrees of supercritical crossover, see [20,21] and references therein.…”

Section: Introductionmentioning

confidence: 99%

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Critical fluctuations and random-anisotropy glass transition in nematic elastomers

et al. 2008

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We carry out a detailed deuterium NMR study of local nematic ordering in polydomain nematic elastomers. This system has a close analogy to the randomanisotropy spin glass. We find that, in spite of the quadrupolar nematic symmetry in 3-dimensions requiring a first-order transition, the order parameter in the quenched "nematic glass" emerges via a continuous phase transition. In addition, by a careful analysis of the NMR line shape, we deduce that the local director fluctuations grow in a critical manner around the transition point. This could be the experimental evidence for the Aizenman-Wehr theorem about the quenched impurities changing the order of discontinuous transition.

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Section: Deuterium Nmr Analysismentioning

confidence: 84%

Section: Nematic-isotropic Transitionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Critical fluctuations and random-anisotropy glass transition in nematic elastomers

et al. 2008

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“…Recently, this fact has been confirmed by NMR and calorimetry measurements [7,28], and we therefore have to be aware that nematic SCLSCEs show spatial variations of their initial director orientation. On the contrary, in our calculations we have assumed an ideal spatially homogeneous initial orientation of the director field.…”

Section: Twist Geometrymentioning

confidence: 90%

Instabilities in nematic elastomers in external electric and magnetic fields

Menzel

Brand

2008

Eur. Phys. J. E

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Abstract. In this paper we study the macroscopic behavior of nematic side-chain liquid single crystal elastomers exposed to an external electric or magnetic field. For this purpose we use the framework of a continuum model. The geometries investigated comprise the bend and the twist geometry known from the classical Frederiks transition in low molecular weight liquid crystals. For the bend geometry we find a laterally homogeneous and a two-dimensional undulatory instability, which may compete at onset. In the case of the twist geometry three instabilities can occur at onset, two of which are two dimensional and clearly show undulations. As a major result we propose how the values of the twist coefficient K2 and the values of the material parameters D1 and D2 connected to relative rotations between the director field and the polymer network can be determined from experimental observations. In addition, we explain why a twist experiment is probably the most suitable set-up in order to measure the material parameter D1.PACS. 61.30.Vx Polymer liquid crystals -61.30.Dk Continuum models and theories of liquid crystal structure -61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

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“…The exact dependence of σ(ε) is affected also by the sample preparation procedure and by the temperature. For LCE materials with a smooth (continuous) phase transition from the nematic to the isotropic phase (also called paranematic phase) [14,15], as the one used in our study, the behavior of σ(ε) is also smooth at all temperatures. The anisotropy of the stress-strain relationship decreases with the increasing temperature, and more or less vanishes at the transition temperature T 0 [16,17].…”

Section: Introductionmentioning

confidence: 91%

Mechanical Manipulation of Diffractive Properties of Optical Holographic Gratings from Liquid Crystalline Elastomers

Bošnjaković

Gregorc

et al. 2018

Applied Sciences

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An appealing property of optical diffractive structures from elastomeric materials is a possibility to regulate their optical patterns and consequently also their diffractive features with mechanical straining. We investigated the effect of strain on diffraction characteristics of holographic gratings recorded in a monodomain side-chain liquid crystalline elastomer. The strain was imposed either parallel or perpendicular to the initial alignment direction of the material. At temperatures far below the nematic-paranematic phase transition, straining along the initial alignment affects mainly the diffraction pattern, while the diffraction efficiency remains almost constant. In contrast, at temperatures close to the nematic-paranematic phase transition, the diffraction efficiency is also significantly affected. Straining in the direction perpendicular to the initial alignment strongly and diversely influences both the diffraction pattern and the diffraction efficiency. The difference between the two cases is attributed to shear-stripe domains, which form only during straining perpendicular to the initial alignment and cause optical diffraction that competes with the diffraction from the holographic grating structure.

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Criticality Controlled by Cross-Linking Density in Liquid Single-Crystal Elastomers

Cited by 40 publications

References 18 publications

Critical fluctuations and random-anisotropy glass transition in nematic elastomers

Critical fluctuations and random-anisotropy glass transition in nematic elastomers

Instabilities in nematic elastomers in external electric and magnetic fields

Mechanical Manipulation of Diffractive Properties of Optical Holographic Gratings from Liquid Crystalline Elastomers

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