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SURFACTANT DESORPTION IN HOMEOTROPIC NEMATIC LAYERS STUDIED BY FLEXOELECTRIC SPECTROSCOPY

L. Todorova1, Y. Marinov1,* , I. Maslyanitsyn2, S. Torgova3, A. G. Petrov1

Affiliation

  1. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko chaussee, 1784 Sofia, Bulgaria
  2. General Physics Institute, Russian Academy of Sciences, 38 Vavilov str., 117942 Moscow, Russia
  3. State Scientific Center of Russian Federation, NIOPIK, 1/4 B. Sadovaya, 103787 Moscow, Russia

Abstract

Homeotropic nematic layers of MBBA and BMAOB liquid crystals, oriented by self assembled films (on glass plates) of dilauroyl phosphatidyl choline (DLPC) and chromolan have been studied by a phase-sensitive flexoelectric spectroscopy method [1-3]. The viscoelastic spectra of these layers, reflecting the surface dissipation of the orientational energy, have been analyzed taking into account a strong (DLPC) or weak (chromolan) surfactant desorption. Surfactant molecules desorb from the surface and dissolve in the nematic, producing a surface gradient of the concentration of the surfactant. A theoretical treatment of the first harmonic [4] has been implemented. The temperature dependence of the thickness of the desorbed subsurface layer of the surfactant was revealed. The surface viscosity was also obtained from the theoretical fits to the spectra. These results are able to give new insights on the physics of the nematic liquid crystal - solid surface interaction, where flexoelectricity and surfactant desorption play a fundamental role..

Keywords

Homeotropic nematic layers, Flexoelectricity, Surfactant desorption.

Submitted at: Dec. 9, 2004
Accepted at: Jan. 26, 2005

Citation

L. Todorova, Y. Marinov, I. Maslyanitsyn, S. Torgova, A. G. Petrov, SURFACTANT DESORPTION IN HOMEOTROPIC NEMATIC LAYERS STUDIED BY FLEXOELECTRIC SPECTROSCOPY, Journal of Optoelectronics and Advanced Materials Vol. 7, Iss. 1, pp. 269-272 (2005)