Effects of molecular geometry on liquid crystalline phase behaviour: isotropic-nematic transition

The effects of range and geometry of a simple attractive square-well on the phase diagram of hard ellipsoids and hard spherocylinders is systematically studied using a simple van der Waals type theory. The orientational single particle distribution function is approximated using the Onsager trial function. The quantitative errors introduced by this are thought to be considerably smaller than the use of the van der Waals approximation, which has been shown to give qualitatively correct phase diagrams for similar models. The phase diagrams obtained for hard ellipsoids and hard spherocylinders of aspect ratios ranging between 3 and 10 with a variety of square-well attractions are found to fall into three general types. The first type shows liquid-vapour coexistence and an isotropic-nematic transition, which meet at a liquid-vapour-nematic triple point. The second type shows a marked widening of the isotropic-nematic biphasic region which pre-empts the liquid-vapour coexistence. The final phase diagram shows a strong destabilization of the nematic phase with respect to the isotropic, which results in a shift of the phase transition to higher densities and pressures as the temperature is lowered.     

The synthesis and mesogenic properties of side chain polymethacrylates with terminal branched groups

The synthesis is described of six polymethacrylates attached through oxytetramethylene and oxyhexamethylene spacers to an azobenzene moiety consisting of branched terminal iso-butoxy, iso-amyloxy and n-amyloxy groups. The monomers show a nematic mesophase while their polymers show an additional higher order smectic C phase. The effects of the terminal branched alkoxy group and the spacers on mesomorphic properties are discussed. The phase characteristics, thermal stabilities and molecular masses of the polymers were investigated by DSC, XRD, TGA and GPC. The polymers were also characterized by UV-vis, IR and NMR spectroscopy.     

Square-well fluid based decoupling approximation for system of hard non-spherical particles with spherical square-wells

A new theory based on the virial equation has been developed to study a system of hard non-spherical particles embedded into square-wells. The theory relies on a mapping of the pair correlation function of the system of interest onto that of spherical square-wells. This is a generalization of the Parsons—Lee theory of pure hard convex bodies. Comparisons show that this theory is superior to previous theories and incorporates them into a common framework. Competition between the excluded volume effect of repulsive forces and the condensation effect of attractive forces has been demonstrated. We have found three types of phase diagrams, among which one exhibits a nematic—nematic phase transition.