Evidence of Supercritical Behavior in Liquid Single Crystal Elastomers

Lebar, Andrija; Kutnjak, Zdravko; Žumer, S.; Finkelmann, Heino; Sánchez‐Ferrer, Antoni; Zalar, Boštjan

doi:10.1103/physrevlett.94.197801

Cited by 75 publications

(80 citation statements)

References 15 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: 58%

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: 58%

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: 70%

“…This special direction then gets locked in or "frozen in" [5], so that no spontaneous breaking of rotational symmetry occurs at the "transition" to the nematic state. Consequently, a state referred to as "paranematic", or supercritical behavior can be observed [6,7]. a e-mail: andreas.menzel@uni-bayreuth.de b e-mail: brand@uni-bayreuth.…”

Section: Introductionmentioning

confidence: 99%

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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“…In order to evaluate the efficiency of the system, the energy needed to increase the temperature from 25 8C (nematic phase) to 60 8C (isotropic phase) was calculated by considering a heat capacity of C p ¼ 2 J Á g À1 Á mol À1 , already reported by ac and relaxation heat capacity measurements, [20] http://doc.rero.ch and the latent heat of the nematic-to-isotropic transition of DH NI ¼ 0.8 J Á g À1 . As a result, the transferred heat for the complete contraction of the LCE is Q ¼ 0.36 J, energy used for the movement of the arm, and friction of the system.…”

Section: Mechanical Testing Of the Microactuatormentioning

confidence: 99%

Photo‐Crosslinked Side‐Chain Liquid‐Crystalline Elastomers for Microsystems

Sánchez‐Ferrer

Fischl

Stubenrauch

et al. 2009

Macro Chemistry & Physics

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Photo‐crosslinkable side‐chain liquid‐crystalline polymers (LCPs) containing photoreactive benzophenone cores are synthesized in order to obtain their corresponding side‐chain liquid‐crystalline elastomers (LCEs). This strategic synthesis allows thin elastomeric films and their integration into microsystems for actuators and micromachines to be obtained. As an example of this principle, a gripper was developed. The position of its arms can be changed by applying voltages from 1.5 to 3.5 V at different rates. Small changes in the liquid‐crystalline elastomer film cause strains of up to 150% in the microdevice and the capacity to move up to 400 times its own mass due to the nematic‐to‐isotropic transformation.magnified image

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Evidence of Supercritical Behavior in Liquid Single Crystal Elastomers

Cited by 75 publications

References 15 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

Photo‐Crosslinked Side‐Chain Liquid‐Crystalline Elastomers for Microsystems

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