Snakes Eating Elephants: Using Selective Withdrawal to Coat Micro Particles

Friday, January 12, 2001 - 4:00pm - 4:30pm
Keller 3-180
Itai Cohen (University of Chicago)
In the Selective withdrawal experiment a suspended tube, whose orifice rests slightly above a water-oil interface, is used to withdraw the fluids. By changing the rate of flow, we control a transition between a state where only oil is withdrawn through the tube and one where water is entrained in a thin spout along with the oil. Understanding the physics of this transition is vital for various engineering applications including the manufacture of coatings for micron-sized particles. Coating is achieved by replacing the water with a pre-polymer solution containing the particles to be coated. These particles are also entrained with the solution and, as they rise, they eventually become larger than the spout width. At this point the spout breaks up and the particles are left with a thin coat of pre-polymer. Depending on the pre-polymer, we harden the coat using chemicals, light, or temperature. We find that the thickness of the coat can be controled by varying the flow rate and controlling the hysteretic effects involved in the transition.