A METHOD FOR THE DETERMINATION OF THE ELASTIC-CONSTANT RATIO K33 K11 IN NEMATIC LIQUID-CRYSTALS

A detailed analysis of the recently proposed [Appl. Phys. Lett. 60, 32 26 (1992)] method for the direct determination of the bend-to-splay bu lk elastic constant ratio (K33/K11) in nematic liquid crystals is pres ented. K33/K11 is directly measured from the optical birefringence pat tern of an escaped-radial nematic director field using the Frank elast ic free-energy approach to determine the stable structure in supramicr ometer capillary tubes with strong homeotropic anchoring conditions. N o external field or a priori knowledge of the anisotropy in magnetic o r electric susceptibility is required. The simple experimental setup u sed is available in most laboratories, making this an attractive and c onvenient technique to probe the elastic character of nematic material s. The results for 5CB and PCH-5 are in good agreement with data obtai ned from conventional electo-optic and magneto-optic techniques.