A SHAPE MODEL FOR THE TWISTING POWER OF CHIRAL SOLUTES IN NEMATICS

The twisting power of chiral probes in nematics is interpreted in term s of a shape model, in which the surface elements of the solute molecu les tend to align with the local director. The theoretical treatment i s based on a previous approach, suitable for relating order parameters in nematics to molecular shape, and leads to the definition of a mole cular pseudo-tenser whose orientational average determines the pitch a nd handedness of the helical macrostructures. Results of numerical cal culations performed for distorted biphenyl and binaphthyl molecules ar e in agreement with the experimental results.