Evaluation of Emulsion Film Thickness at the Nanoscale Level by the Optical Evanescent Wave Effect

The advancement of the knowledge about the rheology and hydrodynamics of thin films assists in a specific manner the industrial applications concerning emulsions and foams. Actually, the stability of these complex systems is largely influenced by the dynamics of the thin interfacial film intervening between approaching or separating droplets or bubbles. During the recent years, the project LIFT (Liquid Film Tensiometer) was supported by the national Italian Space Agency (ASI) with the aim of pursuing fundamental achievements in the field of thin emulsion films. In a future LIFT microgravity mission the film thickness, as the most important film parameter, will be measured at the nanoscale level by two simultaneous complementary methods, namely by the well-established interferometric technique and by a new application of the optical evanescent wave technique. The scope of the poster is the illustration of the above-mentioned new methodology for the evaluation of the film thickness by the evanescent wave technique. Example results are reported for the liquid/liquid system " n-decane/SDS aqueous solution / n-decane ".