Experimental and Computational Analysis of Fluid Interfaces Influenced by Soluble Surfactant

The present contribution is the result of a collaboration between the Max Planck Institute of Colloids and Interfaces and the Technical University of Darmstadt (MMA group). The main objective is to give a quantitative description of fluid interfaces influenced by surfactants, comparing experimental and computational results. Surfactants are amphiphilic molecules subject to ad- and desorption processes at fluid interfaces. In fact, they accumulate at the interface, modifying the respective interfacial properties. Since these interfaces are moving, continuously deforming and expanding, the local time-dependent interfacial coverage is the most relevant quantity. The description of such processes poses severe challenges both to the experimental and to the simulation sides. Two prototypical problems are considered for comparison between experiments and simulations: the formation of droplets under the influence of surfactants and rising bubbles in aqueous solutions contaminated by surfactants. Direct Numerical Simulations (DNS) provide valuable insights into local quantities such as local surfactant distribution and surface tension, but at high computational costs and restricted to short time frames. On the other hand, experiments can give global quantities necessary for the validation of the numerical procedures and can afford longer time frames. The two methodologies thus yield complementary results which help to understand such complex interfacial phenomena