Density-functional theory of the columnar phase of discotic Gay–Berne molecules

Abstract

We propose a density-functional theory for the study of the phase behavior of discotic molecules interacting via a Gay–Berne potential. The attractions are treated perturbatively in a van der Waals-type manner while the virial series of the repulsions is resummed approximately with the inclusion of the exact second-order Onsager result. On this basis we have studied the isotropic (I)–nematic (N)–columnar (Co) phase behavior for various aspect ratios of the discotic molecules. For small aspect ratios (i.e., large nonsphericities) the phase diagram is found to involve a I–N–Co triple point where the two I–N and N–Co first-order transitions are transformed into a direct I–Co first-order transition. For larger aspect ratios the domain where the N-phase is stable shrinks and disappears above a critical value of the aspect ratio. When compared to the available simulation data it is found that the theory underestimates this critical aspect ratio.