Steric molecular theory for multiple smectic-Aphases

Molecular-lattice-theory results reveal that the steric (hard-repulsive) packing of rigid cores and partially flexible tails can explain the relative stabilities of the smectic-$A_1$, smectic-$A_d$, and higher-temperature and lower-temperature nematic (including reentrant-nematic) liquid-crystalline phases, and the isotropic liquid phase. These phases and transitions between them are presented as a function of temperature, pressure, tail-chain length and flexibility, and orientational and positional order of the molecules for different systems. Critical exponents calculated at the smectic-$A_d$ to nematic transitions are consistent with an identification of the fraction of one-dimensional positional alignment (i.e., the fraction of segregated packing of cores with cores and thus of tails with tails) of the molecules in the smectic-$A_d$ phase as an order parameter.