Eur. Phys. J. E 6, 181-188 (2001)
Spontaneous thermal expansion of nematic elastomers
A.R. Tajbakhsh and E.M. TerentjevCavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, United Kingdom emt1000@cam.ac.uk
(Received 25 June 2001 and Received in final form 29 September 2001)
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,
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.
61.41.+e - Polymers, elastomers, and plastics.
61.30.-v - Liquid crystals.
46.25.Hf - Thermoelasticity and electromagnetic elasticity (electroelasticity, magnetoelasticity).
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
