Flexoelectric polarization in nematic liquid crystals measured by a field on-off pyroelectric technique

A novel technique based on the pyroelectric effect is developed for making direct measurements of the flexoelectric polarization P _f in hybrid aligned nematic cells. The pyroelectric response is measured first in the field-off regime and then with the bias field applied. The latter allows a direct comparison of P _f with the field-induced polarization over the whole range of the nematic phase of the standard compound 5CB. The sum of the flexoelectric coefficients (e ₁+e ₃) is shown to be negative, and its dependence on the nematic order parameter does not follow a simple law (linear or quadratic), as has been predicted theoretically. The dynamics of P _f is discussed in terms of the order parameter fluctuations. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 220–225 (10 February 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.