Correlating molecular structure and surface forces in confined liquid films

Area of Science:

• Surface science
• Colloid and interface science
• Spectroscopy

Background:

• Thin films are crucial in foams and as models for confined liquids.
• Traditional methods link film thickness to disjoining pressure but lack molecular detail.
• Understanding molecular origins of film stability requires advanced techniques.

Purpose of the Study:

• To investigate molecular origins of thin film stability using combined spectroscopic techniques.
• To probe the structure of confined films and the forces governing them.
• To elucidate ion-specific and chain length effects on surfactant-stabilized foam films.

Main Methods:

• Coupled a Thin Film Pressure Balance with UV/Vis, IR, and Raman spectroscopies.
• Used IR spectroscopy for model-free water core thickness determination.
• Employed Raman spectroscopy to analyze surfactant adlayers and aqueous structures.
• Systematically varied halide counterions (Br-, Cl-, F-) and surfactant chain lengths (C12, C14, C16).

Main Results:

• Water structure varied with confinement, while surfactant properties remained constant with disjoining pressure.
• Counterion identity significantly affected monolayer dissociation (F- > Cl- > Br-).
• Spectroscopic methods accurately determined water and surfactant layer thicknesses without models.
• Revealed molecular-level insights into confined film structure and interfacial chemistry.

Conclusions:

• Combined spectroscopy offers a powerful method for studying confined films at the molecular level.
• Ion-specific interactions play a key role in the stability of surfactant films.
• This approach extends foam film studies beyond macroscopic properties to fundamental interfacial processes.