Correlating molecular structure and surface forces in confined liquid films

Surfactant surface excess and molecular orientation were independent of disjoining pressure across the studied range, whereas water structural features varied with confinement. Counterion identity strongly influenced monolayer dissociation, following the order Br^- < Cl^- < F^-, consistent with headgroup binding affinities. The combined spectroscopic approach resolved both core water and surfactant layer thicknesses without reliance on model assumptions. This methodology provides a powerful new route to interrogate molecular structure in confined films, extending the scope of foam film studies beyond macroscopic stability to the fundamental chemistry of interfaces.