Font Size:
Hard colloidal rods in complex confinement: density functional theory vs. experiment
##manager.scheduler.building##: Edificio Santa Maria
##manager.scheduler.room##: Auditorio San Agustin
Date: 2019-07-08 11:45 AM – 03:30 PM
Last modified: 2019-06-15
Abstract
Despite their simplicity, (anisotropic) hard particles have become a standard model for colloidal systems, which can be effectively studied within classical density functional theory (DFT). Fundamental measure theory (FMT) and its recent generalizations allow to predict the phase behavior of such a fluid solely from the shape of the individual particles. Such density functionals, which are exact in the low-density limit, have been successfully applied to hard rods in three dimensions. However, implementing the most general framework, fundamental mixed measure theory (FMMT), usually requires systematic approximations of the comprised two-body term [R. Wittmann, M. Marechal, and K. Mecke, J. Phys.: Cond. Matt. 28, 244003 (2016)].
Recent experimental advances allow for the synthesis of colloids with a nearly hard interaction that can be analyzed on the single-particle level. Slices of a system of such silica rods confined in a three-dimensional chamber under gravity can be considered a quasi-two-dimensional fluid that exhibits typical liquid-crystal behavior in confinement [L. B. G. Cortes, Y. Gao, R. P. A. Dullens and D. G. A. L. Aarts, J. Phys.: Cond. Matt. 29, 064003 (2017)].
In this presentation, we apply the two-dimensional version of FMMT to a system of hard discorectangles. We first map out a full phase diagram including stable isotropic, nematic, smectic and crystalline phases [R. Wittmann, C. E. Sitta, F. Smallenburg, and H. Löwen, J. Chem. Phys. 147, 134908 (2017)], demonstrating that the free numerical minimization of the full FMMT functional is feasible in two dimensions, even for highly inhomogeneous systems. The second-order isotropic-to-nematic transition line is obtained analytically.
Finally, we show some new results for the density profiles in complex confinement, e.g., an annulus, where the bulk order phenomena compete with the requirement to match the confining geometry. With the focus on relatively dense system, we compare the topology of the predicted smectic structures to particle-resolved snapshots of experiments with silica rods.
Recent experimental advances allow for the synthesis of colloids with a nearly hard interaction that can be analyzed on the single-particle level. Slices of a system of such silica rods confined in a three-dimensional chamber under gravity can be considered a quasi-two-dimensional fluid that exhibits typical liquid-crystal behavior in confinement [L. B. G. Cortes, Y. Gao, R. P. A. Dullens and D. G. A. L. Aarts, J. Phys.: Cond. Matt. 29, 064003 (2017)].
In this presentation, we apply the two-dimensional version of FMMT to a system of hard discorectangles. We first map out a full phase diagram including stable isotropic, nematic, smectic and crystalline phases [R. Wittmann, C. E. Sitta, F. Smallenburg, and H. Löwen, J. Chem. Phys. 147, 134908 (2017)], demonstrating that the free numerical minimization of the full FMMT functional is feasible in two dimensions, even for highly inhomogeneous systems. The second-order isotropic-to-nematic transition line is obtained analytically.
Finally, we show some new results for the density profiles in complex confinement, e.g., an annulus, where the bulk order phenomena compete with the requirement to match the confining geometry. With the focus on relatively dense system, we compare the topology of the predicted smectic structures to particle-resolved snapshots of experiments with silica rods.