Studying vapor-liquid transition using a generalized ensemble.

Homogeneous vapor-liquid nucleation is studied using the generalized Replica Exchange Method (gREM). The generalized ensemble allows the study of unstable states that cannot directly be studied in the canonical ensemble. Along with replica exchange, this allows for efficient sampling of the multiple states in a single simulation.

Electrostatic and induction effects in the solubility of water in alkanes.

Experiments show that at 298 K and 1 atm pressure, the transfer free energy, μ, of water from its vapor to liquid normal alkanes CH (n=5…12) is negative. Earlier it was found that with the united-atom TraPPE model for alkanes and the SPC/E model for water, one had to artificially enhance the attractive alkane-water cross interaction to capture this behavior. Here we revisit the calculation of μ using the polarizable AMOEBA and the non-polarizable Charmm General (CGenFF) forcefields.

Competition between Intra- and Intermolecular Association of Chain Molecules with Water-like Solvent.

Fluid properties and phase behavior of systems such as glycol ethers, carboxylic acids, and proteins are affected by the competition between intra- and intermolecular hydrogen bonding. Here we study this competition by extending Wertheim's first-order thermodynamic perturbation theory to include intramolecular hydrogen bonding in chain molecules in the presence of an explicit water-like solvent. The theory derived here is found to be in good agreement with molecular simulation.

Isolating the non-polar contributions to the intermolecular potential for water-alkane interactions.

Intermolecular potential models for water and alkanes describe pure component properties fairly well, but fail to reproduce properties of water-alkane mixtures. Understanding interactions between water and non-polar molecules like alkanes is important not only for the hydrocarbon industry but has implications to biological processes as well. Although non-polar solutes in water have been widely studied, much less work has focused on water in non-polar solvents.

Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface.

Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory.

Wertheim's association theory applied to one site patchy colloids: beyond the single bonding condition.

We apply Wertheim's theory to develop an equation of state for one site patchy colloids where the patch can bond multiple times. We allow for the possibility of ring formation without the introduction of empirical parameters and show that for moderate patch coverage the infinite series of chain graphs is well represented by the first two terms. The theory is found to be in excellent agreement with new NVT and NPT Monte Carlo simulations.