(722b) The Breakup of an Oil Drop Containing a Colloidal Suspension in an Electric Field

When an electric field is applied across a drop of fluid suspended in another fluid, electric stresses are generated at the interface, which deform the drop and cause it to break above a critical field strength. In this work, the breakup modes of a squalane drop in silicone oil is studied experimentally, first for a pure squalane drop, and then for a squalane drop with added polyisobutylene succinimide (OLOA 11000) surfactant. A drop of pure squalene undergoes breakup with pointed ends from which tiny drops are ejected, a breakup mode called tip streaming. The addition of the surfactant changes the breakup mode to end pinching, characterized by the formation of lobes at the two ends of the drop, which eventually detach into drops having a size comparable to the original drop. Using axisymmetric boundary integral computations, we predict Marangoni stresses generated by a non uniform distribution of surfactant to change the breakup mode. Next, the breakup modes of a drop containing a colloidal suspension of carbon black with OLOA is probed. It is observed that a drop of a stable suspension of carbon black has the same breakup mode as a drop with surfactant alone, i.e., without added carbon black. However, a drop of an unstable suspension shows a drastically different breakup mode as compared to a drop with surfactant alone. These drops get stretched and start forming asymmetric lobes that develop into fingers and eventually disintegrate in an inhomogeneous fashion. We attribute this inhomogeneity in breakup to the unstable nature of the suspension. Our work shows that breakup modes of a drop of a colloidal suspension under electric fields could be used to quickly assess the stability of the suspension.