SHAPE MODEL FOR ORDERING PROPERTIES OF MOLECULAR DOPANTS INDUCING CHIRAL MESOPHASES

An extension to chiral phases of a model derived previously to interpr et orientational properties in liquid crystal solvents of molecules wi th arbitrary shape leads, quite naturally, to the definition of a trac eless chirality tensor, useful for predicting the structures of twiste d nematics induced by chiral solutes. The magnitude and handedness of the helical pitch in the induced chiral phase depend on the interplay of the chirality tensor components and the ordering of the different a xes of the chiral probe in a given nematic solvent. The effect of chan ging the molecular structure of the solute and the temperature is disc ussed for a number of typical dopants, including biphenyl, binaphthyl and heptalene derivatives. Although the model has been derived in a fo rm suitable for application to induced cholesteric structures, it cont ains the basic ingredients to account for the physical behaviour of ch iral smectic-C mesophases.