Capillary force on colloidal particles in a freely suspended liquid thin film

The dynamic behavior of micron-sized polystyrene latex particles confined in a free-standing liquid film is experimentally studied. When the thickness of the film is less than the particle diameter and varies depending on position, the particles are accelerated toward the thicker region. Using a simple geometrical model and hydrodynamic theory, we calculate the capillary force on the particle. The drag coefficient of the particle is found to depend on the thickness of the film from the value of near zero to the Stokes' drag coefficient.