Pinchoff and satellite formation in surfactant covered viscous threads

The breakup of viscous liquid threads covered with insoluble surfactant is investigated here; partial differential equations governing the spatio-temporal evolution of the interface and surfactant concentrations are derived in the long wavelength approximation. These one-dimensional equations are solved numerically for various values of initial surfactant concentration, surfactant activity and the Schmidt number (a measure of the importance of momentum, i.e., kinematic viscosity, to surfactant diffusion). The presence of surfactant at the air-liquid interface gives rise to surface tension gradients and, in turn, to Marangoni stresses, that affect drastically the transient dynamics leading to jet breakup and satellite formation. Specifically, the size of the satellite formed during breakup decreases with increasing initial surfactant concentration and surfactant activity. The usual self-similar breakup dynamics found in the vicinity of the pinchoff location for jets without surfactant Eggers 1993, however, are preserved even in the presence of surfactant; this is confirmed via numerical solutions of the initial boundary value problem.

Co-authored with Matar O. K. and Papageorgiou D. E.

To appear subject to revisions Phys Fluids