Surfactant effects on contact line alteration of a liquid drop in a capillary tube

In this paper, the effect of an insoluble surfactant on the moving contact line of an interface between two fluids filling a capillary tube is studied. The governing equations are the incompressible Navier-Stokes equations with the couple of Eulerian fluid variables and Lagrangian interfacial markers. In our model, capillary force plays a role in the fluids motion. Here, we propose that besides lowering the interfacial tension which affects the capillary force, the surfactant also decreases the surface tension between fluids and a solid surface. That condition is applied to the unbalanced Young condition at the contact line. The front-tracking method is used to solve numerically the free boundary motion of the interface. Results show that the surfactant has a significant effect on the motion of the contact line. (paper)