Scaled particle theory of hard rods in two dimensions: Effect of variable rod size and attractive interactions

The thermodynamic properties of hard-rod fluids confined to a plane are derived using scaled particle theory, and restricting the number of possible orientations to six. Results for simple systems are compared with earlier results for three-dimensional spherocylindrical systems. Mixtures of rods of different lengths are also studied as possible models for systems in which the constituent molecules may change conformation. Upon inclusion of a van der Waals attractive potential energy, interesting and unusual phase changes can occur.