The nematic-smectic transition in suspensions of slightly flexible hard rods

A second virial theory is presented to study the influence of a slight flexibility on the nematic-smectic A transition in fluids of freely rotating hard rods. The spinodal is located by performing a bifurcation analysis of the equation describing the single-particle distribution function. A closed expression for the structure factor is also derived. The structure factor diverges at the spinodal, confirming the results of the bifurcation analysis. The theory shows that flexibility i) shifts the critical concentration to higher values and ii) decreases the smectic layer spacing. It is concluded that flexibility destabilizes the smectic state, and that sufficiently flexible rods may not form a smectic at all.