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Soft Matter and Biological Physics

Eur. Phys. J. E 4, 183-192

Surface and flexoelectric polarization in a nematic liquid crystal 5CB

L.M. Blinov1, 2, M.I. Barnik1, H. Ohoka2, M. Ozaki2, N.M. Shtykov1 and K. Yoshino2

1  Institute of Crystallography, Russian Academy of Sciences, 117333, Leninsky prosp. 59, Moscow, Russia
2  Department of Electronic Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan


(Received 28 February 2000 and Received in final form 5 September 2000)

The temperature dependence of the surface polarization has been measured for both the planar and homeotropic orientation of a nematic liquid crystal at a solid substrate. A conventional liquid crystal 5CB, pure and doped with an azo-dye, was used in cells with controlled asymmetry for light absorption. The measurements have been made by a pyroelectric technique using short pulses of a YAG laser to create a temperature increment. The latter, in turn, was measured independently by a novel time-resolved "optical thermometer"technique monitoring temperature-dependent birefringence by a He-Ne laser beam. In accordance with the symmetry of the order parameter, the surface polarization has different sign for the two orientations, its magnitude ranges from -4 to +2pC/m. The same technique has been used for the measurement of the flexoelectric polarization in hybrid cells. The sum of the flexoelectric coefficients is e1+e3=-13pC/m at 25$^{\circ}$C.

61.30.-v - Liquid crystals.
77.70.+a - Pyroelectric and electrocaloric effects.
77.84.Nh - Liquids, emulsions, and suspensions; liquid crystals.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001