A molecular simulation study of aqueous solutions of amines and alkanolamines: mixture properties and structural analysis

Abstract

The behaviour of different aqueous solutions of amines and alkanolamines has been studied in terms of the intermolecular radial distribution function using the anisotropic united atom force field for amines and alkanolamines and the TIP4P/2005 force field for water. We have also calculated the excess volumes and mixture densities at several concentrations, comparing in all cases with available experimental information. Different pair distribution functions have been qualitatively analysed for several molecules, namely methylamine, ethylenediamine, diethylenetriamine, monoethanolamine, diethanolamine and methyldiethanolamine. A qualitative study of the intramolecular structure of multifunctional amines in aqueous solutions has also been included. In general, we have found that amines at all concentrations prefer to be surrounded by water molecules rather than by amine molecules. Although the force field overestimates the excess volumes of alkanolamines in aqueous solutions, their sign and non-monotonic behaviour are well represented for all the studied systems. Finally, a very good numerical agreement has been found for the predictions of the mixture densities.