Addition of spheres to a suspension of rods stabilizes the smectic phase. The illustration on the bottom is of a Monte Carlo simulation of aligned hard sphero-cylinders. The volume fraction is 30% and the rods are in a nematic liquid crystal phase - all pointing in the same direction, but no long range positional correlations in the positions of the rods. If the volume fraction were increased to about 50% then a smectic phase would be formed. On the top, spheres have been added to the suspension, but rods removed so that the total volume fraction is also 30%. Now, smectic ordering is observed. The positions of the rods have long range correlations in the direction parallel to the long axis, but no correlations in the two directions perpendicular to the rod axis. Because addition of spheres induces smectic layering at a total volume fraction that is less than is needed to induce smectic order for a pure rod system, we say that addition of spheres stabilizes the smectic phase.
There are two QuickTime animations of constant pressure Monte Carlo simulations of (1) the nematic - smectic transition in pure rod suspensions, and (2) the nematic - lamellar (or intercalated smectic) transition in rod/sphere mixtures. In each case the starting condition is low pressure and density where the rods are in a nematic phase. There is a large, sudden pressure jump and the system compresses and densifies. This increase in concentration drives the phase transition.