Bulg. J. Phys. vol.31 no.1-2 (2004), pp. 49-54

Surface Dissipation in Homeotropic Nematic Layers Characterized by Orientant Desorption

L. Todorova1, Y. Marinov1, I. Maslyanitsyin2, S. Torgova3, A.G. Petrov1
1Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
2Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, 117292 Moscow, Russia
3SSC RF "NIOPIK". Organic Intermediates & Dye Institute, B. Sadovaya 114, Moscow, Russia
Abstract. Viscoelastic spectra of homeotropic nematic layers of MBBA oriented by self-assembled films with different degree of desorbtion: high (dilauroyl phosphatidyl choline, DLPC) and low (chromolan) have been studied by a phase-sensitive flexoelectric spectroscopy method. Orientants desorb from the surface and dissolve in the nematic, producing a surface gradient of concentration of the orientant. Extended theoretical treatment was implemented resulting in spectral shapes, which have been successfully compared to the experiment, yielding information about the surfactant gradient. These results permit us to reveal the existence and the structure of a desorbed layer of orientant in homeotropic oriented nematics.

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