Aqueous solutions of hydroxyl-functionalized ionic liquids: Molecular dynamics studies

A series of aqueous solutions of 1-(n-hydroxyalkyl)-3-(n-hydroxyalkyl) imidazolium bromide ([HOC(n)C(m)OHIm][Br], with n and m = 2, 6,10 and 14) were studied by atomistic molecular dynamics simulations. Structural properties were characterized by the radial distribution functions between different pairs, angular distributions and aggregation numbers. Dynamics of the system has been investigated by computing the diffusion of the ions and molecules. Structures of the aggregates formed depend upon the length of the hydroxyalkyl chains. The long-distance spatial correlations observed in solutions with cations having long chain substituent are arising due to the formation of intercalated structures. A thin film like structure is formed in solutions having longer hydroxyalkyl chains, with the structure stabilized by the dispersion interactions between the interdigitated alkyl chains and the hydrogen bond formation between the hydroxyl group of a cation with head group of a different cation. Anions are dispersed near the surface of the film. (C) 2020 Elsevier Inc. All rights reserved.