Structure and dynamics of dibutylphosphate/n-propylamine ionic liquid: A multi-scale theoretical study

Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (2018) that mixtures of short aliphatic chains compounds at room temperature, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, display ionic liquid–like behavior ascribed to phosphate-to-amine proton transfer. To gain a detailed molecular picture of the system structure and dynamics and to understand the molecular mechanisms at the basis of the observed behavior, in the present study a combination of ab initio Density Functional Theory (DFT) calculation and ab initio Molecular Dynamics (AIMD) simulation has been carried out on DBP + PA clusters. It was found that in these systems the proton transfer is a cooperative process boosted by the concerted interactions of more than one DBP-PA pair. Moreover, classical molecular dynamics (MD) simulations of large DBP + PA systems showed that, triggered by steric effects due to the alkyl chains of both components, these interactions are able to build an extended network of polar domains embedded in an apolar environment of alkyl chains.