Extended H-Bonding through Protic Ionic Liquids Facilitates the Growth and Stability of Water Domains in Hydrophobic Environment

Abstract

Discrete water domains in hydrophobic environment find relevance in aerosols, oil refinery, the human body, etc. The interfacial microstructure plays a crucial role in the stability of such water domains. Over the decades, the amphiphile-induced electrostatic interaction is considered to be the major stabilizing factor operating at these interfaces. Here we take the representative water/AOT/oil microemulsion to show that creating a strong Hbonding network through suitable additive, such as protic ionic liquid (IL) at the interface, helps both the growth and stability of water domains in the hydrophobic phase. On the other hand, common electrolytes and aprotic ILs fail to replicate such behavior as seen by Raman, Fourier transform infrared spectroscopy, dynamic light scattering (DLS), and electron microscopy measurements. Experimental results are further supported by the all-atomic molecular dynamics (MD) simulations that showed extended Hbonding mediated by the protic IL cations that were localized at the interface. High temperature DLS and rheology studies have shown greater thermal stability and mechanical strengths of our biocompatible microemulsions, which have potential to become suitable templates for in situ synthesis of nanoparticle and various organic compounds.

Effects of Ionic Liquids on Aqueous Urea Solutions: Insights into the Ionic Liquid-Assisted Protein Renaturation

“…These liquids exhibit large electrochemical stability, negligible vapor pressure, low flammability, and high ionic conductivity. , Due to these unique properties, the applications of ILs are ever expanding in biological sciences, − chemical processes, , batteries, and a multitude of other areas. , Moreover, by careful selection of cations and anions, a large number of ILs can be designed with tunable properties . This prompted the strategy of designing ILs appropriate for particular applications, , with this novel class of liquid being regarded as “designer solvents” . Interestingly, the structural organizations of the ILs change in the presence of low-to-moderate quantities of water ,− that enhances the applicability of the ILs manyfold. ,,, Moreover, addition of water not only reduces the viscosity of the ILs but also preserves the properties of the ILs when a requisite amount of water is added .…”

“…12,13 Moreover, by careful selection of cations and anions, a large number of ILs can be designed with tunable properties. 14 This prompted the strategy of designing ILs appropriate for particular applications, 15,16 with this novel class of liquid being regarded as "designer solvents". 14 Interestingly, the structural organizations of the ILs change in the presence of low-to-moderate quantities of water 8,17−19 that enhances the applicability of the ILs manyfold.…”

Structural Transitions at the Water/Oil Interface by Ionic-Liquid-like Surfactant, 1-Butyl-3-methylimidazolium Dioctyl Sulfosuccinate: Measurements and Mechanism

“…System compositions has been tabulated in Table S1. Force field parameters of AOT and IPM were taken from the reports of Abel et al 33 and Bardhan et al, 25 respectively. The interaction parameters and atomic charges on [BMIM] + were generated from ab initio calculations.…”

“…TIP3P water model was used, and the protocol for MD simulations was similar to our previous work. 25 Both the RM systems were energy minimized and subsequently equilibrated for 1 ns without any restrain. Equilibrated systems were subjected to production run under NPT ensemble at 300 K temperature with 1 fs time steps.…”

“…22,23 More recently, Senapati and co-workers have shown the occurrences of enhanced H-bonding interaction at the water/oil (W/O) interface of [Na][AOT]based microemulsions due to added IL, which the authors correlated to the observed increased stability and growth of these RM droplets. 24,25 The counterion of [AOT] also plays a major role in defining the micellar properties. For example, Levinger and co-workers 26 have shown that the change in alkali metal counterions has little impact on the water/[Na][AOT]/ oil microemulsions, whereas Mg 2+ can perturb the water structure significantly.…”