Dimensional cross-over of hard parallel cylinders confined on cylindrical surfaces

TL;DR

This paper develops a fundamental-measure density functional for parallel hard curved rectangles on cylindrical surfaces, revealing phase behaviors like smectic and crystalline phases depending on the cylinder radius ratio.

Contribution

It introduces a novel density functional for curved rectangles on cylindrical surfaces derived from lower-dimensional functionals, extending the fundamental-measure theory to curved geometries.

Findings

Smectic phase is most stable for most radius ratios.

Crystalline phase becomes reentrant at R0/R=4.

Transition behavior varies with the ratio R0/R.

Abstract

We derive, from the dimensional cross-over criterion, a fundamental-measure density functional for parallel hard curved rectangles moving on a cylindrical surface. We derive it from the density functional of circular arcs of length $\sigma$ with centers of mass located on an external circumference of radius $R_0$. The latter functional in turns is obtained from the corresponding 2D functional for a fluid of hard discs of radius $R$ on a flat surface with centers of mass confined onto a circumference of radius $R_0$. Thus the curved length of closest approach between two centers of mass of hard discs on this circumference is $\sigma=2R_0\sin^{-1}(R/R_0)$, the length of the circular arcs. From the density functional of circular arcs, and by applying a dimensional expansion procedure to the spatial dimension orthogonal to the plane of the circumference, we finally obtain the density functional of curved rectangles of edge-lengths $\sigma$ and $L$. The DF for curved rectangles can also be obtained by fixing the centers of mass of parallel hard cylinders of radius $R$ and length $L$ on a cylindrical surface of radius $R_0$. The phase behavior of a fluid of aligned curved rectangles is obtained by calculating the free-energy branches of smectic, columnar and crystalline phases for different values of the ratio $R_0/R$ in the range $1<R_0/R\leq 4$; the smectic phase turns out to be the most stable except for $R_0/R=4$ where the crystalline phase becomes reentrant in a small range of packing fractions. When $R_0/R<1$ the transition is absent, since the density functional of curved rectangles reduces to the 1D Percus functional.