Small particles can adsorb strongly at fluid interfaces and form monolayers which can be studied using a Langmuir trough. For sufficiently large particles the monolayers can be viewed microscopically. The driving force for particle adsorption is the concomitant removal of fluid/fluid interface. For very small adsorbed particles, the free energy of forming the three-phase contact line around particles (hence the line tension) may also contribute significantly to the free energy of adsorption. Adsorption can be enhanced by having areas of particle surface with different wettability (Janus particles). Monolayers have structures dependent on lateral interactions between particles; for particles at the oil/water interface, electrical repulsion through oil is often the dominant interaction, which can give rise to highly ordered monolayers. Adsorbed particles can either inhibit or facilitate the formation of stable thin liquid films, depending on particle wettability.
Ion-Specific Effects on Equilibrium Adsorption Layers of Ionic Surfactants
