Phase diagrams of binary mixtures of hard rods in an external orientational field
Abstract
We
study a binary mixture of hard spherocylinders with the same diameter (D) and different length (L2>L1) in the absence
and presence of a static external electric (magnetic) field on the basis of the Onsager theory. In the
zero field, we find that the usual isotropic–nematic phase transition takes place only between the length
ratio (L2/L1) of 1–2.9, the reentrant phenomenon occurs for L2/L12.7, and the nematic–nematic phase transition
starts to be stable for L2/L1>2.9. In the external field, the isotropic–nematic transition is replaced by
a weakly ordered nematic–nematic transition. The increasing external field strength shifts the transition towards
lower densities and narrows the density gap terminating the first order transition at
a critical
point. The critical
field strength
is found to increase rapidly with increasing length ratio.