Condensed Matter


Viscosidade Anisotrópica Dos Cristais Líquidos (Anisotropic Viscosity of Liquid Crystals)

Authors: Manuel Simões F., Ricardo Gobato

The anisotropic viscosity of the liquid crystals (CL) is one of the most challenging properties of these materials, it was discovered in 1935 by Miesowicz, when he showed that CLs are non-Newtonian fluids, exhibiting viscosities that are direction dependent when subjected to an external field . Over this time, a tremendous amount of experimental and theoretical research has been devoted to the subject, but a microscopic theory satisfactory to it has never been found. The kinetic approach of Doi had for some time been the most accepted microscopic theory for nematic viscosity, but even having the great merit of producing a free expression of the adjustable parameters, which captures the essence of the phenomena, providing a semimicroscopic explanation for the origin of Its anisotropy, there are well documented divergences with the experimental data, being unable to describe the essential aspects of the phenomenology observed in these systems, especially when considering the range of the nematic phase. The objective of this work is to study the contribution of the characteristic geometry of the nematic / molecule micelle to the viscosity of the nematic liquids. Throughout this work, we use the word geometry of the nematic grain, or simple geometry of the grain, to designate the geometry that a nematic micelle / molecule acquires under the thermal vibration. This concept does not appear to be common in the theory of NCLs, but arises naturally from Gennes's theory of parameters for NLCs. In addition, to increase the contribution of grain geometry to nematic viscosity we will use the Hess and Balls conforming approach to formulate the fundamentals of nematic viscosity.

Comments: 1 Page. Panel presented at the XV Week of Physics of the State University of Londrina, Paraná, Brazil, September 2010.

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