Water-mediated aggregation of 2-butoxyethanol

Water plays an important role in mediating hydrophobic interactions, and yet open questions remain regarding the magnitude, and even the sign, of water-mediated contributions to the potential of mean force between a pair of oily molecules dissolved in water. Here, the water-mediated interaction between 2-butoxyethanol (BE) molecules dissolved in water is quantified using Raman multivariate curve resolution (Raman-MCR), molecular dynamics (MD) simulations, and random mixing (RM) predictions. Our results indicate that the number of contacts between BE molecules at concentrations between 0.2 M and 1 M exceeds RM predictions, but is less than some MD predictions. Moreover, the potential of mean force between BE molecules in water has a well depth that is shallower than the direct interaction between 1-ethoxybutane chains in the gas phase, and thus the water-mediated contribution to BE aggregation is repulsive, as it pulls BE molecules apart rather than pushing them together. Water plays an important role in mediating hydrophobic interactions, and yet important open questions remain regarding the magnitude, and even the sign, of water-mediated contributions to the potential of mean force between a pair of oily molecules dissolved in water.