Columnar phases of discotic spherocylinders

Abstract

The liquid crystal phase diagram of the discotic hard spherocylinder fluid is investigated by Monte Carlo simulations. Thickness-to-diameter aspect ratios within L/D=0.2-0.5 are considered. Three distinct columnar phases are found, namely, a hexatic interdigitated phase (D(hi)), a hexatic ordered phase (D(ho)), both with long-range spatial correlations, and a hexatic disordered phase (D(hd)), in which the columns become fluidlike. Local domains of stacked particles are also observed in the isotropic phase. The stability of the D(ho) and D(hd) phases is favored with increasing anisotropy of the particle shape. As a consequence, the packing fraction versus the aspect ratio representation of the phase diagram features D(ho)-D(hd)-I and D(hi)-D(ho)-I triple points. The study involved the development of an efficient algorithm to compute the shortest distance between two oblate spherocylinder particles. The study provides a general coarse-grain methodology to explore discotic behavior, with fundamental advantages against alternative molecular models.

Phase behavior of hard colloidal platelets using free energy calculations

“…6(c)], χ I f (1) II can be estimated to be of order 1 for all aspect ratios. Equation (8) shows that Gibbs ensemble simulations for weakly first order transitions (ρ c II − ρ c I ρ c I , ρ c II ) have to be performed on either very large systems or at a value of N /V chosen such that N I N II . However, the Gibbs ensemble method has been used previously 5,37 to find the isotropic-nematic phase transition and, therefore, we also made an attempt to locate the isotropic-nematic coexistence using Gibbs ensemble simulations for OHSC with L/D > 0.…”

“…8,13,14,[18][19][20][21][22][23] Therefore, we will only briefly describe the shape of our platelets. The OHSC consists of a flat cylindrical core with diameter σ and height L, and a toroidal rim, with tube diameter L (see Fig.…”

“…We detect overlaps between OHSC using the efficient, although partially numerical algorithm, which was introduced in Ref. 8. Since that work, the overlap algorithm has been improved and some brief remarks on these changes are presented in the Appendix.…”

“…8,14,15 an isotropic fluid at the lowest densities for all aspect ratios L/D, a (discotic) nematic phase at low densities and aspect ratio L/D 0.1, and phases in which the OHSC form aligned columns at high densities. However, using the pressure annealing method, we found two different crystals, X tilted and X aligned , which were found to be stable (using free energy calculations) in, respectively, the lower and 46 the transition from D ho to D hd , where the correlation length of the particles within a column becomes smaller than a certain threshold value (e.g., a few particle dimensions) is not sharp at all; the spatial correlations within a column will always have a finite correlation length.…”

“…[14][15][16] In Refs. 8,14, and 15, the phase diagram of oblate hard spherocylinders (OHSC) was tentatively explored using direct simulations. Three columnar phases were found for 0.1 ≤ L/D ≤ 0.5, where L is the thickness of the platelet and D its diameter.…”