Surface reorientation dynamics of nematic liquid crystals
INFM and Dipartimento di Fisica, Universita di Pisa,
Via Buonarroti ed.B 2, 56126 Pisa, Italy
2 Groupe de Dynamique des Phases Condensées (UMR CNRS/UMII 5581) , Université de Montpellier II, Place E. Bataillon, 34000 Montpellier, France
Published online: 15 October 1999
In this paper we report an experimental investigation on the dynamics of the azimuthal director reorientation at a nematic-solid interface. Three qualitatively different kinds of substrates have been investigated: I) intrinsically anisotropic SiO-substrates (60°-evaporation), II) isotropic SiO-substrates (0°-evaporation) and III) rubbed PVA-substrates. In the case II), an in-plane anisotropy was induced cooling slowly the thermotropic nematic liquid crystal (NLC) from the isotropic phase in the presence of a 0.75 T magnetic field. The reorientation dynamic of the surface azimuthal director angle at the switching-on and off of a magnetic (or electric) field has been investigated. All the substrates show comparable azimuthal anchoring energies and two dynamic regimes: a fast dynamic response, driven by the bulk director reorientation and an extremely slow reorientation. The slow dynamics is explained in terms of anisotropic adsorption of NLC molecules on the solid substrate and is well represented by a stretched exponential.
PACS: 61.30.Gd – Orientationnal order of liquid crystals; electric and magnetic field effects on order / 78.20.Ci – Optical constants: refractive index, complex dielectric constant, absorption, reflexion and transmission coefficients, emissivity
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999