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Title: The Local Field and Orientational Order Parameter in Nematic and Smectic Liquid Crystals
Authors: Mukhebi, Michael Abraham Lutta
Keywords: Local Field and Orientational Order Parameter -- Nematic and Smectic Liquid Crystals
Issue Date: Dec-1995
Publisher: Egerton University
Abstract: Numerous experimental and theoretical investigations have been carried out on the refractive indices of liquid crystal compounds particularly nematogenic compounds in the crystalline, liquid crystalline, and liquid phases. This is with a view to determining the orientational order parameter,1 S, at various temperatures, its variation with temperature as well as molecular structure, the study of which goes a long way in choosing a nematogenic compound with a suitable nesomorphic range for use in display devices as well as other applications, and also in synthesizing compounds with the required mesonorphic range. Of late even the smectic compounds in general and their modifications like the smectic C‘ phase in particular have also assumed importance in display devices and other applications. We have therefore in this thesis chosen a particular homologous series of liquid crystalline compounds exhibiting Smectic A(SA) and Smectic B(Sa) modifications which are also uniaxial positive. The polarization field is therefore the same nature as in the nematic phase. Though extensive ¢nd accurate birefringence data for these compounds is available, density data as well 'as refractive index data in the crystalline and isotropic is not available. We have therefore linked electric effective susceptibilities Xe and X0 to the only data available, Ha and fie, the extraordinary and ordinary refractive indices of compounds in liquid crystalline phases, and calculated the Lorentz factors Le and Lo. Furthermore we have also made use of bond polarizability procedure and estimated the orientational order parameter as well. Sincere attempts have also been made to justify the approach used. Interesting results are obtained with regard to Lorentz factors at different temperatures and variations of optical anisotropy with temperature . Variation of its total change in going from one phase to another is correlated with the number of C—C bonds in the end groups. The significance and validity of the S factors and its correlation with structure is also discussed. Limitation of the bond polarizability approach is also briefly mentioned.
Appears in Collections:Faculty of Science

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