Molecular Origin of the Sign Preference of Ion- Induced Heterogeneous Nucleation in a Complex Ionic Liquid–Diethylene Glycol System

Heterogeneous nucleation on charged seeds has been shown to frequently prefer a given sign of electrical charge (anion or cation), at constant seed size and (apparent) chemical composition. For some systems, this sign preference can be readily understood in terms of individual chemical interactions. However, experiments are in general unable to provide satisfying molecular-level explanations for the sign preference of chemically complex systems. Here, we experimentally demonstrate a positive sign preference for charged ionic liquid seeds (CILS) with diethylene glycol vapor (DEG) and explain the physicochemical origins of this preference via quantum chemical calculations. The computational results show that all enthalpies and free energies for adsorption of DEG onto the CILS clusters are lower for the positively charged seeds compared to those for the negatively charged seeds. The main reason for this difference is the stronger hydrogen bonds in the cationic clusters originating from the ability of imidazolium-based cations to act as hydrogen bond acceptors.