| To advance understanding of the thermodynamic properties of complex liquid mixtures, molecular-thermodynamic attention is given to several types of asymmetric mixtures: asphaltene-containing crude oils, water-hydrocarbon mixtures with or without salt, and aqueous saline solutions of proteins and colloids. The phase behavior of these liquid mixtures is important for optimum design of industrial processes including production of petroleum and natural gas, separation of protein mixtures, and synthesis of new materials. The objective is to provide molecular-thermodynamic models for describing thermodynamic properties of these industry-oriented liquid mixtures.; Our model for an asphaltene-containing crude oil represents asphaltenes by attractive hard spheres, resins by attractive hard-sphere chains, and all other components by a continuous medium that affects interactions between asphaltene-asphaltene, asphaltene-resin, and resin-resin pairs. We consider explicitly associations between asphaltene and asphaltene, and between asphaltene and resin. Thermodynamic properties are described in the McMillan-Mayer framework using the statistical-associated-fluid theory (SAFT). Our model can semi-quantitatively explain essentially all experimental observations concerning asphaltene precipitation from crude oils. This model has been applied to identify approximately the operating conditions at the onset of asphaltene precipitation, and the amount of precipitation under various petroleum-reservoir conditions. For the prevention of asphaltene precipitation, we recommend the use of amphiphiles that like both asphaltenes and the oil medium, but not the resins.; For water-hydrocarbon mixtures with or without salt, we have developed theoretically-based extensions of the Peng-Robinson equation of state by including associations and electrostatic interactions. Illustrative examples show that these extensions are successful for correlating vapor-liquid equilibria for hydrocarbon-water systems with or without salt. However, because SAFT cannot properly represent water structure, it is not possible to give a good representation of liquid-liquid equilibria at temperatures where hydrophobic effects are significant.; We have built two membrane osmometers and measured osmotic pressures of bovine serum albumin in aqueous sodium-chloride solutions at a variety of pH and salt concentrations. Two theories have been proposed to represent the experimental data. The first is based on the Carnahan-Starling equation for repulsion and the osmotic second virial coefficient for attraction. The second is based on the random-phase approximation. Agreement with experiment is only approximate. Improvement of theoretical representation requires not a more sophisticated statistical-mechanical model, but a better potential of mean force.; For colloidal dispersions, we have shown from Monte-Carlo simulations that the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is inappropriate to describe the potential of mean force between like-charged macroions in an electrolyte solution containing divalent counterions. We obtained the potential of mean force between two identical negatively-charged macroions in 1:1, 1:2, 2:1 and 2:2-electrolyte solutions. Contrary to the DLVO theory, our simulation results show attractions in 2:1 and 2:2-electrolyte solutions. We find that attraction follows from the internal-energy contribution of counterion mediation.; Finally, we present an alternate derivation of Wertheim's first-order perturbation theory for associated fluids and for chain fluids. Our derivation explicitly illustrates physical assumptions and limitations of this theory. We find that Wertheim's theory cannot describe structural properties of strongly hydrogen-bonded fluids, and it is not valid for fluids containing very long chains.; Results reported here contribute toward a better understanding of liquid mixtures containing components that differ strongly in molecular siz... |
