Measurements of dynamic forces between drops with the AFM: Novel considerations in comparisons between experiment and theory

Abstract

Dynamic forces between a deformable tetradecane oil drop (radius of curvature ≈ 25 μm) anchored on the cantilever of the Atomic Force Microscope (AFM) and similar oil drops (radii of curvature 80 to 500 μm) on the substrate in aqueous electrolyte with added sodium dodecyl sulfate surfactant have been studied. Measurements were made over a range of scan rates that span the range of Brownian velocities of such emulsion drops. The adsorbed anionic surfactants impart a stabilising electrical double layer repulsion between the drops so coalescence was not observed under present conditions. Force-displacement data follow reversible trajectories at low scan rates (<0.5 μm s-1) but exhibit increasin..