Enhanced stability of layered phases in parallel hard spherocylinders due to addition of hard spheres

There is increasing evidence that entropy can induce microphase separation in binary fluid mixtures interacting through hard particle potentials. One such phase consists of alternating two-dimensional liquidlike layers of rod s and spheres. We study the transition from a uniform miscible state to thi s ordered state using computer simulations, and compare results to experime nts and theory. We conclude the following: (1) There is stable entropy driv en microphase separation in mixtures of parallel rods and spheres. (2) Addi ng spheres smaller than the rod length decreases the total volume fraction needed for the formation of a layered phase, and therefore small spheres ef fectively stabilize the layered phase; the opposite is true for large spher es. (3) The degree of this stabilization increases with increasing rod leng th.