Combined AFM−Confocal Microscopy of Oil Droplets: Absolute Separations and Forces in Nanofilms

Abstract

Quantitative interpretation of the dynamic forces between micrometer-sized deformable droplets and bubbles has previously been limited by the lack of an independent measurement of their absolute separation. Here, we use in situ confocal fluorescence microscopy to directly image the position and separation of oil droplets in an atomic force microscopy experiment. Comparison with predicted force vs. separation behavior to describe the interplay of force and deformation showed excellent agreement with continuum hydrodynamic lubrication theory in aqueous films less than 30 nm thick. The combination offorcemeasurementand3Dvisualizationofgeometricseparationandsurfacedeformationis applicable to interactions between other deformable bodies.