Impact of Colloidal Stability on the Electric Field Driven Break-up of Non-Aqueous Suspension Drops

We examine the breakup of an oil drop containing a colloidal suspension of carbon black particles under a uniform DC electric field. A drop of squalane containing a fixed concentration 3.3 g/L of carbon black and varying amounts of polyisobutylene succinimide dispersant (OLOA) is exposed to field strengths that yield drop breakup. When a particle-loaded drop containing an appreciable concentration of OLOA (30 parts OLOA per 100 parts carbon black, pph OLOA) is subjected to an electric field of 2.5 kV/cm, the drop exhibits homogeneous breakup via the pinch-off of bulbous ends. Increasing the applied field to 5.3 kV/cm yields an inhomogeneous, nonaxisymmetric drop breakup mode. Since the added dispersant stabilizes the colloidal suspension of carbon black particles in this system, we observe no appreciable qualitative differences between the breakup of a drop containing both particles and dispersant, and a drop containing dispersant alone. When the concentration of dispersant is decreased to a value of 2 pph OLOA, the colloidal suspension becomes unstable within the timescale of the experiment, and the drop achieves inhomogeneous breakup via the formation of lobes that turn into fingers and eventually disintegrate. Here, the drop containing both particles and dispersant achieves a radically different field-induced breakup mode from a drop containing dispersant alone. The experimental systems in this study are modeled using the boundary integral method, which assumes that both the drop and medium phases are homogeneous. We implement our computations to assess the importance of surface charge transport and the heterogeneity of the particle-loaded drop. The method depicted in this study may be implemented to deduce the colloidal stability of particle-loaded drops exposed to electric fields.