Nematic Elastomers: The Dependence of Phase Transformation and Orientation Processes on Crosslinking Topology

Greve, Andreas; Finkelmann, Heino

doi:10.1002/1521-3935(20011001)202:14<2926::aid-macp2926>3.0.co;2-3

Cited by 53 publications

(32 citation statements)

References 11 publications

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“…In a heated cell, the sample was stretched by two stepping motors at strain steps of about 0.5%, the stress being measured by a force-transducer. The time between each deformation step was taken as 2 h to allow full relaxation of the sample [34].…”

Section: Methodsmentioning

confidence: 99%

Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

et al. 2011

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We report effects of disorder due to random cross-linking on the nematic to smectic-A phase transition in smectic elastomers. Thermoelastic data, stress-strain relations and high-resolution x-ray scattering profiles have been analyzed for two related compounds with a small and a larger nematic range, respectively, each for 5% as well as 10% cross-links. At 5% cross-link density the algebraic decay of the positional correlations of the smectic layers survives in finite-size domains, providing a sharp smectic-nematic transition. At an increased cross-link concentration of 10% the smectic order disappears and gives way to extended short-range layer correlations. In this situation neither a smectic-nematic nor a nematic-isotropic transition is observed anymore. The occurrence of disorder at a relatively large cross-link concentration only, indicates that smectic elastomers are rather resistant to a random field. The temperature dependence of the correlation lengths and thermoelastic behavior suggest a shift to a "parasmectic" regime of a first-order smectic-isotropic transition.

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Section: Methodsmentioning

confidence: 99%

Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

et al. 2011

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“…The values of the parameters A and ̅ can be deduced from the values of refractive indices of the material at room temperature and at T >> T0. For side-chain LCE materials of the type as the one used in our study, those values are ne(T >> T0) ~ no(T >> T0) = 1.58, ne(T0 − 50 °C) = 1.66, and no(T0 − 50 °C) = 1.54 [37,38], which gives ̅ = 2.5 and A = 0.077. The resulting dependence of ne(T,T0) is shown as the black solid line in Figure 8a.…”

Section: Discussionmentioning

confidence: 89%

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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“…[31] Even if all these procedures were developed for nematic elastomers, by modifying the liquid crystalline core, using a mixture of different mesogens or changing the ratio between monovinyl and divinyl monomers, it is possible to obtain materials with tuneable transition temperatures and different mesomorphicb ehaviour. [32,33] In all cases, this strategy requires a mechanical stretching to obtain the aligneds amples (with the exception of the cholesteric one). Thus, samples with big size can be easily prepared whereas, on the other hand, only one alignment direction can be programmed for the whole film and the procedure lacks in versatility also regarding the microfabrication and the patterning methods.…”

Section: Chemical Routes To Liquidcrystalline Elastomersmentioning

confidence: 99%

Advances in Cell Scaffolds for Tissue Engineering: The Value of Liquid Crystalline Elastomers

Martella

Parmeggiani

2018

Chemistry A European J

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Recent discoveries evidenced that many cells organize into well-aligned nematic domains, showing also their topological defects and suggesting the liquid crystalline order to be necessary for some biological functions. These evidences were described as the basis for the development of a new area of research in which polymeric liquid crystals were developed to exploit and promote cell adhesion and proliferation towards tissue regeneration. To address the requirements of tissue engineering, new biocompatible materials must be designed and synthesized to support cell adherence and growth together with nutrient transport under physiological condition. This Minireview presents a journey that, starting from the first discovery of liquid crystalline phases in biological (natural) materials with different structures and physical-chemical properties, will inform readers of the very recent application of liquid crystal polymeric materials as functional cell scaffolds to address current tissue engineering issues.

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Nematic Elastomers: The Dependence of Phase Transformation and Orientation Processes on Crosslinking Topology

Cited by 53 publications

References 11 publications

Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

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

Advances in Cell Scaffolds for Tissue Engineering: The Value of Liquid Crystalline Elastomers

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