Liquid-Liquid Phase Separation Produces Fast H-Bond Dynamics in DMSO-Water Mixtures

Area of Science:

• Physical Chemistry
• Spectroscopy
• Nanoscale Science

Background:

• Liquid-liquid phase separation (LLPS) is prevalent in complex mixtures.
• The physical behavior of nanoconfined liquids, especially during LLPS, remains poorly understood.
• Dimethyl sulfoxide (DMSO) is an amphiphilic molecule exhibiting concentration-dependent properties in aqueous mixtures.

Purpose of the Study:

• To investigate the hydrogen-bond (H-bond) dynamics of nanoconfined liquids in DMSO-water mixtures.
• To probe the microscopic environments experienced by different molecules within these mixtures.
• To characterize the relationship between nanoscale phase separation and ultrafast dynamics.

Main Methods:

• Utilized ultrafast two-dimensional infrared (2D IR) spectroscopy.
• Employed formamide (FA) and dimethylformamide (DMF) as vibrational probes of varying polarity.
• Performed molecular dynamics (MD) simulations to complement experimental data.

Main Results:

• Picosecond H-bond dynamics were fastest in the intermediate DMSO concentration regime (20-50 mol %).
• Nanoscale phase separation creates unique microscopic environments for each probe molecule.
• MD simulations revealed dynamics spanning femtoseconds to nanoseconds.

Conclusions:

• Identified a novel liquid environment termed
• local bulk
• characterized by ultrafast H-bond dynamics similar to bulk water.
• Despite local heterogeneity due to nanoscale phase separation, the dynamics in this
• local bulk
• environment are surprisingly similar to bulk water.
• The findings provide new insights into the physical behavior of nanoconfined liquids during phase separation.