Microstructures of hydrophobic ionic liquids via tuning water networks: Theoretical and experimental investigations

Abstract

Ionic liquid (IL)/water mixtures with specified structures can aggregate or assemble in solutions to form clusters, which can be widely used as templates in the design and preparation of functional materials. However, microstructures with different water contents remain unclear, especially near the phase boundary. Herein, we explored the effects of water on the structure of a hydrophobic IL, [C2mim][Tf2N], and proposed the formation of nanodomains as the composition approached phase separation points through the combination of experiments, molecular dynamics, and statistical analyses. Results show that xw = 0.25 is a turnover point near the phase boundary, and some aggregations among water molecules, cations, and anions gradually begin to form two phase regions. Below xw = 0.25, the mixtures are a uniformly dispersed system, and the interstices formed between [C2mim]+ and [Tf2N]− can only accommodate the water monomer. When xw > 0.25, density profiles show that [C2mim][Tf2N] makes a distinct boundary with water molecules. The analyses of the microstructure and size of nanodomains in this work may provide a theoretical basis and new strategy for improving the design of soft templates for porous materials.