Dynamical aspects of the formation of the mesomorphic state structure

Abstract

In terms of the self-consistent phonon field method generalized with regard to the orientational degrees of freedom the dynamics of the formation of the mesomorphic state structure at the activation of the molecular crystal oscillations is studied. The reasons for the existence and for the stability of the partially ordered media with liquid-crystalline and plastic packing of the molecules are substantiated. The dependencies of the dynamical crystal characteristics versus temperature are calculated. From the analysis of the librational and translational anharmonicities evolution at the temperature alteration the energetic relations for the transition of the molecular crystal into the mesostate are established. It is shown that the anharmonic processes bound-up with different degrees of the molecules freedom give an essentially unequal contribution to the development of the dynamical instability of the system. The mutual correlation between the structural instability type, the molecular crystalline anisotropy coefficient and the molecular interaction anisotropy factor are investigated. The behaviour of the critical values as functions of the system anisotropy parameters is considered. Conclusions are drawn regarding the crystal lattice disarrangement in the pretransitional regions of liquid-crystalline and plastic mesogeneity.