Continuous isotropic-nematic transition of partially flexible polymers in two dimensions

Two-dimensional, partially flexible polymers interacting with each other through the Onsager-like excluded-volume interaction are shown to exhibit a second-order, isotropic-nematic transition at a sufficiently high density. The instability of the free energy under the influence of a nematic state is investigated and the critical density at which the isotropic-nematic phase transition takes place is determined analytically. It is shown that both second- and fourth-rank order parameters must be included in order to deduce a Landau expansion of the free energy.