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The
azimuthal anchoring
coefficient Wa we usually determine by measuring
surface deviation
angle Δφ
of LC director in the twist cells. The
measuring principle depends on the value
of Wa.
In
case of low Wa (10-3-10-2
erg/cm2),
thick samples can be used for which Mauguin regime of light propagation
takes place. In
asymmetric cells, containing rubbed
PI substrate and tested substrate, deviation Δφ
occurs only on tested substrate so that it can be easily estimated by
analyzer
rotation angle.
In
case of stronger Wa (>10-2 erg/cm2),
only
in thin cells easily detectable Δφ
can be achieved. Since Mauguin regime does not work in these cells, new
measuring methods are required. Usually, we apply a spectroscopic
method set
forth in [V.A. Konovalov et al., SID’00
DIGEST,
p.
620] and displayed below.
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