Incorporating particle flexibility in a density functional description of nematics and cholesterics

We describe a general implementation of the Fynewever-Yethiraj density functional theory (DFT) for the investigation of nematic and cholesteric self-assembly in arbitrary solutions of semi-flexible polymers. The basic assumptions of the theory are discussed in the context of other generalised Onsager descriptions for flexible polyatomic systems. The location of the isotropic-to-nematic phase transition is found to be in good agreement with molecular simulations for elongated chains up to relatively high polymer flexibilities, although the predictions of the theory in the nematic regime lead to gradual underestimations of order parameters with decreasing particle stiffness. This shortcoming is attributed to increasing overestimations of the molecular conformational entropy in higher-density phases, which may not be easily addressed in the formalism of DFT for realistic particle models. Practical consequences of these limitations are illustrated through the application of DFT to systems of near-persistence-length DNA duplexes, whose cholesteric behaviour is found to be strongly contingent on their detailed accessible conformational space in concentrated solutions.