Quantitative and structural analysis of water association in water-lithium bromide-1

Identifier:  imarina:9287121

Handle: https://hdl.handle.net/20.500.11797/imarina9287121

Authors:  Latorre-Arca, David; Soledad Larrechi, M; Salavera, Daniel; Coronas, Alberto; Rodriguez-Fortea, Antonio; Rivera-Pousa, Alejandro; Mendez-Morales, Trinidad; Varela, Luis M

Abstract:
In this work we report on the quantitative and structural analysis of the water association in water-lithium bromide-1,3-dimethylimidazolium chloride mixtures using multivariate curve resolution based on alternating least squares (MCR-ALS) of Near Infrared (NIR) spectra and Molecular Dynamics (MD) simulations. (NIR + MCR) methodology was used to determine the bulk water amount, as well as the mole ratio between the H2O/absorbent of the solvated structures. Measurements were performed for ternary mixtures prepared with absorbent mole fraction (LiBr + [Dmim][Cl]) from 0 to 0.5987 and the MD simulations were carried out at selected compositions within this concentration range. The results revealed the existence of three water chemical environments: bulk water in absence of solutes, bulk water coexisting with solvated water and solvated water. The comparative analysis of results with those obtained for binary mixtures (H2O + LiBr) and (H2O + [Dmim][Cl]) evidenced that the water amount that remains as bulk water in ternary solutions is higher than in binary mixtures. Classical MD simulations for five different concentrations of absorbent confirmed that water environment evolves from being essentially coordinated with other water molecules in the most diluted system, to being mainly surrounded by monoatomic ions for the most concentrated mixture. Furthermore, higher interaction between the ions appears with increasing the absorbent mole fraction, which is confirmed by Car-Parrinello MD simulations.