Nematic-isotropic phase transition in polar liquid crystals. 2. Role of dispersion interactions
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The present study furthers the development of the theory of the nematic-isotropic phase transition in the system of rodlike particles with large longitudinal dipoles. The effect of dispersion interactions between single molecules (monomers) and molecular pairs (dimers) on the transition temperature is considered. The crucial point of the approach used is existence of dimers in the system. Dispersion interactions are estimated within the framework of the model in which molecules consist of spherical blocks interacting according to the Lennard-Jones law. The direct pair-correlation functions are approximated by spherical invariants forming a complete system of functions. Then, these correlation functions are varied in order to study the behavior of the phase-transition temperature depending on the choice of the molecular model. It is shown that, depending on the molecule shapes, dimers can either destroy or stabilize the nematic order. It is also shown that the presence of dimers in the system decelerates an increase of the transition temperature (and, in many instances, can even reduce it) with an increase in the value of the molecular dipole.
KeywordsPhase Transition Transition Temperature Liquid Crystal Single Molecule Dispersion Interaction
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