We present a new equation of state for hard chain fluids. This equation of state is developed by applying an extension of Wertheim’s theory for associating fluids to a nonspherical reference fluid. Since the equation of state is developed in a similar manner to the statistical associating fluid theory (SAFT) we call this improved equation of state SAFT-Dimer (SAFT-D). The equation of state requires only the contact values of the hard sphere and hard disphere site–site correlation functions as input. We compare the compressibility factor from SAFT and SAFT-D with molecular simulation data for flexible hard chains with chain lengths of 16, 51, and 201 segments. The second virial coefficient and compressibility factor from SAFT-D are in better agreement with molecular simulation results than the generalized Flory dimer, TPT2, and Percus–Yevick compressibility equations of state.
A perturbation density functional theory for the competition between inter and intramolecular association J. Chem. Phys. 136, 154103 (2012); 10.1063/1.3703015Mean field theory for the intermolecular and intramolecular conformational transitions of a single flexible polyelectrolyte chain A new theory to explain the competition between inter-and intramolecular association in flexible hard chain molecules is presented. The theory has been tested through comparisons with Metropolis Monte Carlo simulation results. For intermolecular association we use Wertheim's theory which has been shown to be accurate for intermolecular association in flexible associating hard chain molecules. For intramolecular association we use a theory we developed for intramolecular association in the absence of intermolecular association. These two theories are combined to develop a theory for the competition between inter-and intramolecular association. The new theory is in good agreement with simulation results and is able to predict some salient features of associating chain molecules. The theory predicts that intermolecular association becomes more important at high densities and that intramolecular association dominates at low density and low temperatures. In addition, theory and simulation show a minimum in the compressibility factor when plotted against the association energy at low density. This minimum is due to the presence of intramolecular association and is not observed for intermolecularly associating fluids.
Due to the flexibility of associating polymer and protein molecules, intramolecular association can have a significant affect on the thermodynamic properties and structure of associating polymer and protein solutions. The equilibrium state is determined by the minimization of the appropriate free energy with respect to intermolecular association between like and unlike species and intramolecular association. As a first step to understanding this competition between intramolecular and intermolecular hydrogen bonding, we have conducted a molecular simulation study of flexible hard chain molecules that intramolecularly associate in the absence of intermolecular association. To explain the simulation results, we have developed a new simple and accurate theory of intramolecular association. By considering the limit of total bonding, we have also developed an accurate equation of state for hard rings. The theory is in good agreement with new molecular simulation results for intramolecularly associating hard chains, rigid hard rings, and bent triatomics. 6880
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