The light intensity I transmitted through a homeotropically oriented nematic liquid crystal slab held between crossed polarizers, as a function of the angle 03B8H of an applied magnetic field, is calculated for oblique light incidence. The presence of singular points in the I vs. 03B8H curve which are related to the elastic constants of the liquid crystal is demonstrated One of these points, found here for the first time, for small angles of incidence depends only on the ratio K33/~a, and allows a direct determination of this ratio. The comparison of the calculated curve I vs. 03B8H with the experimental points taken in a sufficiently wide range of 03B8H values, using K11/~a, K33/~a and An = ne2014 no as best fit parameters, allows a very precise determination of all these constants. The method turns out to be much more sensitive than the usual ones, mostly based on capacitance measurements and it is thus very suitable for determining the behaviour of the elastic constants when the temperature is changed, particularly near the transition point.
|Titolo:||Optical study of the molecular alignment in a nematic liquid crystal in an oblique magnetic field|
|Data di pubblicazione:||1984|
|Digital Object Identifier (DOI):||10.1051/jphys:01984004502035500|
|Appare nelle tipologie:||1.1 Articolo in rivista|