Isotropic-nematic phase diagram for interacting rigid rods on two-dimensional lattices.

The phase behavior of interacting rigid rods of length k (k-mers) on two-dimensional square and triangular lattices has been studied by theoretical calculations in the framework of the lattice-gas model. The process was analyzed by comparing the dependence on coverage of the free energy per site of an isotropic submonolayer of interacting k-mers f(iso)(θ) with that corresponding to a fully aligned (nematic) system f(nem)(θ). The existence of an intersection point between the curves f(iso)(θ) and f(nem)(θ), which is indicative of the occurrence of an isotropic-nematic phase transition in the adlayer, allowed us to obtain the complete (temperature, coverage, k-mer size) phase diagram of the system.