Abstract
We report molecular dynamics simulations of confined liquid crystals using the Gay–Berne–Kihara model. Upon isobaric cooling, the standard sequence of isotropic–nematic–smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules.
Highlights
The reappearance of a thermodynamic phase as the temperature T is lowered (or the pressure P is raised) is termed “reentrance”
The reappearance of a thermodynamic phase as the temperature T is lowered is termed “reentrance”
From the above discussion it is apparent that, though many different LC systems exhibit reentrant behavior, the molecular mechanism leading to a reentrant nematic (RN) has not uniquely been identified, because the analysis has focused on the molecular details
Summary
The reappearance of a thermodynamic phase as the temperature T is lowered (or the pressure P is raised) is termed “reentrance”. Λ. It shows a discontinuous increase at T = 5.2 corresponding to the nematic–smectic A transition, followed at T ≃ 4.5 by a decrease to values characteristic of the nematic phase.
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