| Issue |
Europhys. Lett.
Volume 36, Number 2, October II 1996
|
|
|---|---|---|
| Page(s) | 111 - 116 | |
| Section | Condensed matter: structure, thermal and mechanical properties | |
| DOI | https://doi.org/10.1209/epl/i1996-00195-4 | |
| Published online | 01 September 2002 | |
Biaxial nematic and smectic-A boundaries in thin planar samples of 8OCB aligned by rubbed polyimide *
Centre de Recherches Paul Pascal - Av. A. Schweitzer,
F-33600 Pessac, France
Received:
23
February
1996
Accepted:
2
September
1996
The birefringence of planar 8OCB samples has been measured as a
function of temperature at thicknesses decreasing from 7.2 to 
. The first curve (
) is perfectly
superimposable to the result of conoscopic measurements done with a
homeotropic uniaxial sample, from a minimum of
0.08 close to the isotropic phase up to 0.19 in the smectic-A
phase. For thinner planar samples, one gets an increasing
birefringence (up to 35% more in both phases with a new plateau at
0.26). This means that the bulk uniaxial phase is surrounded by
biaxial boundaries (a few 
thick) where the extreme
indices of refraction lie parallel to the plates. A mean-field model
of long-range interaction is proposed that takes into account the
observed features.
PACS: 61.30.-v – Liquid crystals / 68.45.Gd – Wetting / 78.20.Fm – Birefringence (including stress birefringence, flow birefringence, etc.)
© EDP Sciences, 1996
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