Dynamic Interfacial Tensions of Aqueous Triton X-100 Solutions in Contact with Air, Cyclohexane, n -Heptane, and n -Hexadecane

Measurements of the dynamic interfacial tensions of aqueous Triton X-100 solutions in contact with air, cyclohexane, n -heptane, and n -hexadecane were performed with the drop-volume method using different flow rates for subsequently falling drops. In the longer time range the plots of the dynamic interfacial tension versus 1/ radicalt show linear dependence in all four cases. Additional equilibrium surface tension measurements with the Wilhelmy-plate technique were performed at the interface to air. Equilibrium results from the Wilhelmy-plate measurements and dynamic data extrapolated to t --> infinity at the interface to air coincide well. The extrapolated data from dynamic investigations were used to calculate the maximum adsorption of Triton X-100 via the Gibbs equation at the four interfaces. In order to calculate the equilibrium adsorption at a specific bulk phase concentration the Langmuir-Szyskowski equation was used and from the data it was possible to calculate effective diffusion coefficients via a long time approximation of the Ward and Tordai equation. The resulting amounts of adsorbed surfactant at the four interfaces show acceptable values. The calculated diffusion coefficients at the water/air interface are in the right order of magnitude. For the interfaces to oil the effective diffusion coefficients are smaller due to the solubility of Triton X-100 in the oil phases. Additionally the distribution coefficients between water and the oil phases for Triton X-100 are given.