Exact sum rules and geometrical packing effects in the system of hard rods near a hard wall in three dimensions

Fundamental measure theory for inhomogeneous fluids of nonspherical hard particles

Using the Gauss-Bonnet theorem we deconvolute exactly the Mayer f-function for arbitrarily shaped convex hard bodies in a series of tensorial weight functions, each depending only on the shape of a single particle. This geometric result allows the derivation of a free energy density functional for inhomogeneous hard-body fluids which reduces to Rosenfeld's fundamental measure theory [Phys. Rev. Lett. 63, 980 (1989)10.1103/PhysRevLett.63.980] when applied to hard spheres. The functional captures the isotropic-nematic transition for the hard-spherocylinder fluid in contrast with previous attempts. Comparing with data from Monte Carlo simulations for hard spherocylinders in contact with a planar hard wall, we show that the new functional also improves upon previous functionals in the description of inhomogeneous isotropic fluids.

Bulk and inhomogeneous mixtures of hard rods and excluded-volume polymer: a density functional approach

We present a density functional theory for a mixture of hard rods and polymer modeled as chains of hard tangent spheres which refines the theory proposed in the paper by Phys. Rev. E 68, 062501 (2003)]. The improvement involves a semiempirical formula for the contact value of the sphere-sphere radial distribution function of the sphere and needle reference system, which includes the important depletion effect induced by the needles. The new functional yields slightly broader phase coexistence envelopes but the changes affect mainly the polymer-rich binodal branches. After analyzing the bulk phase behavior the structure of hard-rod-polymer mixture close to a hard wall is examined. An increase of the chain length leads to an increase of the average polymer segment contact value. This behavior may lead to a qualitative difference of the polymer segment profiles: from an effective repulsion of the polymer segments to an effective attraction, which can be observed by a change of sign of the excess adsorption. By analyzing the orientational order parameter profiles we have found that the polymer coils decrease the tendency of needles to adopt anisotropic configurations.

Wetting properties of a hard-spherocylinder fluid on a substrate

A density-functional theory is used to analyze the wetting properties of a fluid made up of hard spherocylinders of a length-to-breadth ratio L/D=5 on a model substrate. The substrate imposes an exclusion boundary condition over the molecular centres of mass, while at the same time favoring a definite molecular orientation, either parallel or perpendicular to the substrate, in a region next to the substrate. The wetting properties of this system are seen to depend on the strength with which the substrate orients the molecules: as the latter is increased, wetting by nematic phase is followed by a region of partial wetting which then leads to reentrant wetting by nematic. The two wetting transitions correspond to wetting films with nematic director perpendicular and parallel to the substrate, respectively. Also, in the region of partial wetting, an anchoring transition occurs in the substrate-nematic interface between two different director configurations (parallel and perpendicular to the substrate). Finally, a metastable wetting transition by isotropic is also obtained. This model considerably enriches the wetting phenomenology of the hard-spherocylinder fluid on substrates, of which only the pure hard wall, with no surface control parameter available, has been considered so far.