Spontaneous thermal expansion of nematic elastomers |
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Authors: | AR Tajbakhsh EM Terentjev |
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Institution: | (1) Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, United Kingdom, GB |
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Abstract: | We study the monodomain (single-crystal) nematic elastomer materials, all side-chain siloxane polymers with the same mesogenic
groups and crosslinking density, but differing in the type of crosslinking. Increasing the proportion of long di-functional
segments of main-chain nematic polymer, acting as network crosslinking, results in dramatic changes in the uniaxial equilibrium
thermal expansion on cooling from the isotropic phase. At higher concentration of main chains their behaviour dominates the
elastomer properties. At low concentration of main-chain material, we detect two distinct transitions at different temperatures,
one attributed to the main-chain, the other to the side-chain component. The effective uniaxial anisotropy of nematic rubber,
r(T) = / proportional to the effective nematic order parameter Q(T), is given by an average of the two components and thus reflects the two-transition nature of thermal expansion. The experimental
data is compared with the theoretical model of ideal nematic elastomers; applications in high-amplitude thermal actuators
are discussed in the end.
Received 25 June 2001 and Received in final form 29 September 2001 |
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Keywords: | PACS 61 41 +e Polymers elastomers and plastics – 61 30 -v Liquid crystals – 46 25 Hf Thermoelasticity and electromagnetic elasticity (electroelasticity magnetoelasticity) |
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