Interfacial mechanics of drop deformation of viscous and anisotropic fluids
Abstract
The interfacial mechanics of deforming drops was studied. Steady state drop shapes of fluids with a yield-stress behavior were examined. Shapes were found that were inconsistent to the Laplace-Young equation, which equates the hydrostatic pressure drop across an interface with the mean curvature of the interface times the surface tension. In order to understand the experimental data a boundary element method was developed for solving axisymmetric free-surface time-dependent Stokes flows. This method solves the problem by obtaining the solution on the boundary and thus presents many advantages compared to traditional finite element techniques. The problem of a deforming drop in an infinite domain was solved. New results on the details of drop breakup were obtained. Unstable drops were found to deform and develop three daughter droplets joined together in an extending tail from the mother droplet. This appears to correspond to the onset of drop breakup. By examining the internal solution it was found that stress minima and maxima occur in the daughter droplets and that some internal circulation has begun even before the breakup. The deformation of a drop hanging from a solid substrate was also studied. The imposed contact line boundary condition and the accuracy of the curvature calculations limited the program to mostly unstable drops (small surface tension). For the unstable hanging drops the stress on the axis showed a double peak right before breakup. This was attributed to relaxation of the surface tension forces that occurs even before breakup was completed. The simulations revealed large stress concentrations near the contact line. Also internal stress levels increase from the solid substrate to the tip of the drop indicating that if the fluid had a yield behavior its interface would yield nonuniformly. This would produce shapes that are not described by the steady-state Laplace-Young equation.
Degree
Ph.D.
Advisors
Wiest, Purdue University.
Subject Area
Chemical engineering
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