Ion Pairing and Molecular Orientation at Liquid/Liquid Interfaces: Self-Assembly and Function

Area of Science:

• Physical Chemistry
• Surface Science
• Supramolecular Chemistry

Background:

• Molecular orientation is crucial for interface functionality but difficult to measure.
• Buried liquid/liquid interfaces present unique challenges for experimental probing.
• Supramolecular assemblies at interfaces are key to novel functions.

Purpose of the Study:

• To investigate molecular orientations at buried oil/aqueous interfaces.
• To understand how salt addition affects self-assembled oligomer structures.
• To elucidate the mechanisms behind salt-induced orientational changes.

Main Methods:

• Vibrational sum-frequency generation (VSFG) spectroscopy.
• Numerical polarization analysis.
• Atomistic molecular dynamics (MD) simulations.

Main Results:

• Oligomer orientation at oil/aqueous interfaces is sensitive to aqueous salt concentration.
• Salt addition induces changes in oligomer self-assembly and tail orientation.
• Anionic effects, ion pairing, and altered solvation/H-bonding networks drive these changes.

Conclusions:

• Quantitative insights into salt-modulated molecular orientations at buried interfaces.
• Demonstrated the role of competitive ion effects in self-assembly.
• Findings support the design of functional interfaces for chemical separations and biomimetic applications.