Oscillations of Sessile Drops of Surfactant Solutions on Solid Substrates with Differing Hydrophobicity

The paper reports results of experimental studies on the dynamic behavior of surfactant solution drops on substrates with differing hydrophobicity. Contact angle oscillations observed immediately after the drop deposition are studied, and a mechanistic interpretation of this phenomenon is put forward. The major emphasis is put on the physicochemical aspects of surfactant action, including the dynamic wetting enhancement and the effect of surface tension relaxation on the frequency of drop oscillation, which are characteristic of surfactant solutions. Appropriate scaling relations describing the drop dynamics are derived.