Surface and smectic layering transitions in binary mixtures of parallel hard rods

D. de las Heras, Y. Martínez-Ratón, and E. Velasco
Phys. Rev. E, 81, 021706, (2010)     DOI: 10.1103/PhysRevE.81.021706
Full text: journal, pdf

The surface phase behavior of binary mixtures of colloidal hard rods in contact with a solid substrate (hard wall) is studied, with special emphasis on the region of the phase diagram that includes the smectic A phase. The colloidal rods are modeled as hard cylinders of the same diameter and different lengths, in the approximation of perfect alignment. A fundamental-measure density functional is used to obtain equilibrium density profiles and thermodynamic properties such as surface tensions and adsorption coefficients. The bulk phase diagram exhibits nematic-smectic and smectic-smectic demixing, with smectic phases having different compositions; in some cases they are microfractionated. The calculated surface phase diagram of the wall-nematic interface shows a very rich phase behavior, including layering transitions and complete wetting at high pressures, whereby an infinitely thick smectic film grows at the wall via an infinite sequence of stepwise first-order layering transitions. For lower pressures complete wetting also obtains, but here the smectic film grows in a continuous fashion. Finally, at very low pressures, the wall-nematic interface exhibits critical adsorption by the smectic phase, due to the second-order character of the bulk nematic-smectic transition.

Related publications:

1 Phase transitions in nanoconfined binary mixtures of highly oriented colloidal rods (+ info)
2 Capillary Smectization and Layering in a Confined Liquid Crystal (+ info)
3 Capillary effects in a confined smectic phase of hard spherocylinders: Influence of particle elongation (+ info)

Other papers.