MLC

Abstract

Random packing of mixtures of hard spherocylinders and hard spheres are studied for $d \approx L$, where $L$ is the length of the spherocylinder and $d$ the diameter of the spheres. Packing fractions of mixtures of hard spherocylindres with aspect ratios $ 4 < L/D < 20$ and how this packing fraction changes with different concentrations of spheres are investigated. The results obtained are compared with observations of mixtures of sterically stabilized rod-like particles and spheres. These colloidal suspensions of rod-like particles are made with sepiolite clays and have previously been found to show liquid crystal behaviour [1]. The addition of spheres to a colloidal rod suspension affects the isotropic-nematic phase transition that occurs in pure suspensions. One might expect that the addition of spheres would lead to a wide phase gap between rod-rich and sphere-rich phases [2]. An experimental study did find some evidence for nematic rod domains with spheres accumulating at their grain boundaries [3]. Very easily however these systems got stuck in gel states consisting of (bundles of) rods trapping spheres [3]. Rather than trying to calculate equilibrium phase diagrams, we are therefore investigating random close packed configurations which may resemble the experimental observations more closely.

References [1] Z. X. Zhang and J. S. van Duijneveldt, J. Chem. Phys., 124, 154910 (2006). [2] Henk N.W. Lekkerkerker and Remco Tuinier, Colloids and the Depletion Interaction, Springer, 2011. [3] N. Yasarawan and J.S. van Duijneveldt, Soft Matter, 6, 353-362 (2010).