Surface Affinity of Tetramethylammonium Iodide in Aqueous Solutions: A Combined Experimental and Computer Simulation...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Surface Science

Background:

• Understanding the behavior of electrolyte solutions at interfaces is crucial in various chemical and physical processes.
• Tetramethylammonium iodide (TMAI) is an electrolyte with potential applications where interfacial properties are important.

Purpose of the Study:

• To investigate the surface affinity of tetramethylammonium iodide (TMAI) in aqueous solutions.
• To compare the accuracy of different molecular dynamics force fields in predicting TMAI's interfacial behavior.

Main Methods:

• Surface tension measurements using the pendant drop method across the full solubility range.
• Molecular dynamics simulations employing AMBER, CHARMM, OPLS, and GROMOS force fields.
• Analysis of ion distribution and charge compensation at the liquid-vapor interface.

Main Results:

• TMAI exhibits weak capillary activity, confirmed by pendant drop experiments.
• The AMBER force field accurately reproduces experimental surface tension data.
• Iodide ions demonstrate higher surface affinity than tetramethylammonium cations, with distinct adsorption and depletion layers observed.

Conclusions:

• The study validates experimental findings on TMAI's weak capillary activity.
• Force field selection significantly impacts the accuracy of simulating electrolyte interfaces; charge scaling may be necessary for some.
• The interfacial structure is characterized by preferential iodide adsorption and a diffuse layer of tetramethylammonium cations for charge neutralization.