Molecular simulation and theory of polyatomic associating fluids
Garcia-Cuellar, Alejandro Javier
Chapman, Walter G.
Doctor of Philosophy
In this thesis the thermodynamic properties of model polyatomic molecules with association interactions was studied using molecular simulation and theory. The Metropolis Monte Carlo technique was used to perform simulations and the results were compared with extensions of Wertheim's theory of association (first order thermodynamic perturbation theory, TPT1). Excellent agreement was found for wide ranges of state conditions. The case of a telechelic polymer in an associating solvent was studied. This represented one of the first molecular simulation tests of TPT1 for mixtures. The effect of intramolecular association and ring formation was accounted for by a new statistical mechanical theory. The quantities of both intermolecular and intramolecular bonds that form in the chain can be predicted with theory and obtained from molecular simulation. Thermodynamic properties were also calculated and good agreement was obtained. The limit of complete bonding of the theory for intramolecular association gives an equation of state for cyclic molecules. The case when these cyclic molecules associate is studied for trimer cyclics with one and three bonding sites. The effect of shape and association is captured by the resulting theory. Similar models could be used to study dendritic structures. The agreement with simulation is remarkable for a wide range of densities and bonding energies. The case of a chain molecule with a varying density of bonding sites was simulated along with an associating solvent. The solvent molecules can associate with the chains and with themselves. This is another simulation study of mixtures of molecules with dissimilar sizes. The effect of bonding site density on the distribution of bonds in the solvent and on thermodynamic properties was examined with simulation and theory. TPT1 agrees well with the simulation results.
Physical chemistry; Polymer chemistry; Chemical engineering