Thin Liquid Films

Abstract

The first studies of thin liquid films were inspired by the vivid colors of films surrounding soap bubbles. These liquid films are stabilized by two monolayers of soap molecules adsorbed at both their inner and outer surfaces. The films thin due to gravity, and when their thickness reaches values of the order of 1 μm, beautiful colors are observed, which are familiar to everyone. They arise from interferences between white light reflected by the inner and outer film surfaces. The color changes were studied by Newton who also reported the existence of ``black films'', i.e., films much thinner than the wavelength of light, that reflect so little light that they can no longer be seen by eye (Newton 1704). Black films can be found during the last thinning stages, before films rupture.