DOI: 10.1140/epje/i2002-10114-1
An improved reflectometric method to measure the azimuthal anchoring energy of nematic liquid crystals
S. Faetti and G.C. MutinatiINFM and Dipartimento di Fisica, Università di Pisa, Piazza Torricelli 2, 56126 Pisa, Italy faetti@df.unipi.it
(Received 8 January 2002 and Received in final form 27 February 2003 / Published online: 15 April 2003)
Abstract
Some years ago we developed an automatized reflectometric method to
measure the surface azimuthal anchoring energy of nematic liquid
crystals on an optically isotropic substrate.
This method provides a high
accuracy and sensitivity but requires the use of wedge glass plates and
a sufficiently
high anisotropy
of the intensity reflectivity coefficients. This latter condition
restricts greatly
the number of possible
substrates that can be investigated with this technique.
Here we develop a new reflectometric method which offers
comparable or better accuracy and sensitivity but does not
require wedge plates and high anisotropy of the reflectivity
coefficients. The method is fully
automated and provides a direct measurement of the
azimuthal director angle. The experimental procedure
exploits the dependence of the reflectivity tensor on the surface director
orientation. The measurement of the azimuthal angle does not
require any knowledge of the optical parameters of the nematic
material and of the optically
isotropic substrate, and provides an absolute accuracy
better than
in the whole range 0-360
and a
sensitivity better than
. This reflectometric method can be also used with weakly
anisotropic substrates as well as thin rubbed polymeric layers. In this
latter case, the effective uncertainty in the measurement of the director
azimuthal angle depends on the substrate anisotropy. A simple and direct
experimental procedure to estimate this uncertainty is proposed.
61.30.Gd - Orientational order of liquid crystals; electric and magnetic field effects on order.
78.20.Ci - Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity).
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003
