ELECTROOPTICAL PROPERTIES OF MESOGENIC CHAIN MOLECULES IN SOLUTION AND IN NEMATIC STATE

Electrooptical characteristics of mesogenic chain molecules in solutio n and in mesophase can be described in terms of intra- and intermolecu lar orientational orders. The value and sign of electric birefringence Delta n in a solution of kinetically rigid chain molecules are determ ined by the combination of two factors: intramolecular orientational o rder which depends on the dipolar and anisotropic architecture of the molecule and intermolecular orientational order caused by the action o f the external electric field E. The value and sign of the dielectric anisotropy Delta epsilon of the polymer nematic phase are also determi ned by the combination of intra- and intermolecular orders. However, i n this case the latter is not maintained by the external field but by the nematic potential of the mesophase. Therefore, comparative investi gations of electrooptical properties of polymers in solutions and in n ematic melts make it possible to obtain information about the intra- a nd intermolecular orientational orders of the molecules under investig ation in these two states. These investigations were carried out using the method of electric birefringence in solutions and the method of o rientational deformations of nematic textures in an electric field. Th e objects being investigated were nematogenic dimers and trimers. Expe rimental data obtained for these compounds showed the presence of intr amolecular order in their molecules, which is manifested in the odd-ev en oscillations of the value and sign of Kerr constant K approximate t o Delta n/E(2) in solution and Delta epsilon in the nematic phase when the number of C-C bonds in the methylene spacers of these molecules i s varied. This effect is particularly dramatic in the mesophase where it is enhanced by intermolecular nematic potential.