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Selected Mechanical Properties of Uniaxial Side Chain Liquid Crystalline Elastomers

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Liquid Crystalline Polymers

Abstract

This short review gives an overview of selected mechanical properties of uniaxial nematic side chain liquid crystalline elastomers obtained by measurements of the shear modulus performed in the linear regime as a function of temperature and frequency. It focuses on three closely related topics: (a) the determination of the three main shear moduli of the dry elastomers and the influence of the preparation process on these moduli, (b) the evolution of the shear moduli of the dry elastomers when the latter are progressively swollen by a nematic solvent and (c) the influence of a stretching of the dry elastomers on the shear modulus for the situation where the applied sinusoidal shear is parallel to the stretching direction and perpendicular to the initial orientation of the director (reorientation transition). These experiments lead to the following conclusions: (a) the dry elastomers in their un-stretched state are uniaxial rubbers with an internal variable, which are characterized by a small shear anisotropy in the hydrodynamic regime and a Rouse-like frequency behavior in the viscoelastic regime, (b) the elasticity of the network is Gaussian for the elastomers prepared by photo polymerization of a nematic polymer oriented by an electric field, a magnetic field or a surface treatment of the sample-bearing glass slides, and non-Gaussian for the usual twice cross-linked elastomers oriented by a mechanical stretching of the network formed after the first cross-linking step, (c) the concept of soft or semi-soft elasticity does not apply to the un-stretched elastomers, whatever the way they were formed, (d) the soft elastic response expected for the reorientation transition is not observed for an elastomer prepared by UV irradiation.

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Acknowledgment

First, I would like to thank my colleague D. Rogez for the fruitful and enjoyable collaboration during this research. I also wish to thank H. Pleiner, H. Brand, H. Finkelmann and their Ph.D. students for the numerous stimulating discussions we had over the long period covering the whole of the work on the topic. I also thank F. Brömmel for having working with us on the nematic elastomers prepared by UV irradiation, A. Sanchez-Ferrer for interesting discussions and I. Kulic for a critical reading of the manuscript.

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Authors and Affiliations

  1. Institut Charles Sadron, UPR 22, CNRS/UDS, 23 rue du Loess, BP 84047, Strasbourg, 67034, France

    Philippe Martinoty

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  1. Philippe Martinoty
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Correspondence to Philippe Martinoty .

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Editors and Affiliations

  1. Mechanical and Materials Engineering, Washington State University, Pullman, Washington, USA

    Vijay Kumar Thakur

  2. Mechanical and Materials Engineering, Washington State University, Pullman, Washington, USA

    Michael R. Kessler

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Martinoty, P. (2015). Selected Mechanical Properties of Uniaxial Side Chain Liquid Crystalline Elastomers. In: Thakur, V., Kessler, M. (eds) Liquid Crystalline Polymers. Springer, Cham. https://doi.org/10.1007/978-3-319-20270-9_3

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