Azimuthal anchoring energy at the
interface between a nematic liquid crystal and a PTFE
substrate |
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Authors: | E?Campanelli Email author" target="_blank">S?FaettiEmail author M?Nobili |
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Institution: | (1) INFM and Dipartimento di Fisica dell'Università di Pisa, Via Buonarroti 2, 56127 Pisa, Italy;(2) Groupe de Dynamique des Phases Condensées, Université de Montpellier II, Place E. Bataillon, 34000 Montpellier, France |
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Abstract: | The azimuthal anchoring energy of the nematic liquid
crystal 4-pentyl-4'-cyanobiphenil (5CB) on a
poly(tetrafluoroethylene) (teflon, PTFE) film is measured for
the first time. The PTFE film is deposed using the Wittmann and
Smith technique which consists on rubbing a bar of this polymer
against a glass substrate at a controlled temperature and
pressure. Measurements of the azimuthal anchoring energy are
made with a reflectometric technique which provides high
accuracy and sensitivity. The dependence of the azimuthal
anchoring energy on temperature and on the rubbing pressure is
investigated. The extrapolation length remains virtually
constant in the whole temperature range of the nematic phase
except for an increase of 25% close to the clearing temperature.
The azimuthal anchoring energy is somewhat strong and increases
with increasing the deposition pressure of PTFE. The observation
of a relevant pre-transitional anisotropy of the reflection
coefficients in the isotropic phase proves that the surface
interactions favor an excess of orientational order. Ageing of
the anchoring energy and gliding of the easy axis are
experimentally observed. Both these phenomena suggest the
presence of an anisotropic adsorbed layer of nematic molecules
on the PTFE film. |
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Keywords: | 61 30 -v Liquid crystals 61 30 Hn Surface phenomena: alignment anchoring anchoring transitions surface-induced layering surface-induced ordering wetting prewetting transitions and wetting transitions |
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