Instabilities in nematic elastomers in external electric and magnetic fields
Theoretische Physik III, Universität Bayreuth, 95440, Bayreuth, Germany
2 Max Planck Institute for Polymer Research, P.O. Box 3148, 55021, Mainz, Germany
Accepted: 27 March 2008
Published online: 7 May 2008
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 –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2008