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. It is shown that intramolecular association is most important for shorter chains at low temperature, low density, and high chain concentration. The theory is also extended into a density functional theory formalism to study the effect of intramolecular association on the structuring of the different segments of the molecules close to a hydrophobic surface. Intramolecular association is found to be enhanced close to the surface, with the total density of the system having the most effect on structuring close to the surface.