A method for the determination of the elastic constant ratio K33/K11 in nematic liquid crystals

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Abstract
A detailed analysis of the recently proposed [Appl. Phys. Lett. 60, 3226 (1992)] method for the direct determination of the bend‐to‐splay bulk elastic constant ratio (K33/K11) in nematic liquid crystals is presented. K33/K11 is directly measured from the optical birefringence pattern of an escaped‐radial nematic director field using the Frank elastic free‐energy approach to determine the stable structure in supramicrometer capillary tubes with strong homeotropic anchoring conditions. No external field or a priori knowledge 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 PCH‐5 are in good agreement with data obtained from conventional electo‐optic and magneto‐optic techniques.