GUEST-HOST-MIXTURES - A CORRELATION BETWEEN THE DYES ORDER-PARAMETER WITH THERMODYNAMIC AND STRUCTURAL QUANTITIES

A series of dyes containing a rigid aromatic core of the stilbene/azom ethine type with approximate structural cylindrical symmetry as well a s anthraquinone dyes with more spherical shape were investigated conce rning their influence on thermodynamic properties of the liquid crysta lline material CB5 (4'-Pentyl-4-cyano-biphenyl). Quantities like the t ransition temperatures, the biphasic range and the density discontinui ty at the nematic-isotropic transition were estimated via precise dens ity measurements at different solute concentrations. The derived resul ts like the slopes of the phase transition boundary lines and the resu lting transition entropy were used to evaluate a semiempirical model w hich describes the change of the optical order parameter with the solu te's mole fraction and the solute's structure. Experimentally the opti cal order parameter was estimated using the main transition in the vis ible range, which is parallel to the dye's long axis. The comparison o f the experimentally obtained values with the data derived from our mo del is quite acceptable.