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.