دورية
A New Theory of Nematic Liquid Crystal Mixtures
| العنوان: | A New Theory of Nematic Liquid Crystal Mixtures |
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| المؤلفون: | Counsell, C., Warner, M. |
| المصدر: | Molecular Crystals and Liquid Crystals; October 1983, Vol. 100 Issue: 1 p307-326, 20p |
| مستخلص: | A recent theory of hard rod packing allowing a continuum of rod orientations and a specification of steric constraints rotationally invariant and correct in the isotropic limit is generalized to the multicomponent case. The additional effect of temperature on packing, used in a description of one component thermotropic oematics, is employed here in describing the effects of temperature on lyotropic nematics, that is, where the second component is simple solvent. Complicated phase diagrams characteristic of nematic mixtures are given for the examples of rods of axial ratio x = 5 and x = 50 diluted by solvent. Mixtures of two rod components are solved, the phase diagrams of models of quater-quinque-phenyl and quater-sexiphenyl mixtures being presented as more demanding tests of theory than the one component properties previously calculated.We have generalized a new theory of the dense packing of rods to a description of the phase equilibrium of rod mixtures. Free energies and chemical potentials for many components in either nematic or isotropic fluids were obtained. They were used to solve the two component problems of rods mixed with simple solvent or of rods of one species mixed with rods of another species with different axial ratio. The motivation was partly to examine the influence of temperature on lyotropic systems and partly to look at equilibria in mixtures within a homologous series of rods as a more stringent test of theory than a one component system can offer. As a preliminary the variation of biphasic equilibrium with axial ratio in the athermal limit was also calculated.Our results show that temperature has a rich influence on lyotropic liquid crystal phase diagrams. Rods of moderate length diluted by simple solvent exhibit a re-entrance of nematic-isotropic biphasic equilibrium on cooling. Long rods show a triple and critical point and the three types of biphasic equilibrium anticipated in earlier work.1,5Thermotropic rods diluted by other rods, both species being shorter than the critical axial ratio xcrit, display lense-shaped phase diagrams. We present results for models of mixtures of various polyphenyl homologues. These compounds have previously been chosen as model2,4 for their molecular symmetry and stiffness and for the simplicity of their soft interactions. Clear predictions are made for the phase diagrams of quater-, quinque- and sexiphenyl mixtures. |
| قاعدة البيانات: | Supplemental Index |
| تدمد: | 15421406 15635287 |
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| DOI: | 10.1080/00268948308075360 |