Surface and Smectic Layering Transitions in Binary Mixtures of Parallel Hard Rods Articles uri icon

publication date

  • February 2010

start page

  • 21706

issue

  • 2

volume

  • 81

international standard serial number (ISSN)

  • 1539-3755

electronic international standard serial number (EISSN)

  • 1550-2376

abstract

  • 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.