A detailed analysis of the recently proposed lsqb;Appl. Phys. Lett.60, 3226 (1992)rsqb; method for the direct determination of the bendhyphen;tohyphen;splay bulk elastic constant ratio (K33/K11) in nematic liquid crystals is presented.K33/K11is directly measured from the optical birefringence pattern of an escapedhyphen;radial nematic director field using the Frank elastic freehyphen;energy approach to determine the stable structure in supramicrometer capillary tubes with strong homeotropic anchoring conditions. No external field oraprioriknowledge of the anisotropy in magnetic or electric susceptibility is required. The simple experimental setup used is available in most laboratories, making this an attractive and convenient technique to probe the elastic character of nematic materials. The results for 5CB and PCHhyphen;5 are in good agreement with data obtained from conventional electohyphen;optic and magnetohyphen;optic techniques.
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