Milk Fracking (Apker Award, Undergrad Institution)

When a solution of dish soap, water, and food dye is touched to the surface of cow's milk, something remarkable happens: a symmetric, sharp pointed starburst emerges from the contact point. While an outward expansion is expected due to the Marangoni effect, the appearance of the star tips can only be explained by the fracture of a thin protein film at the milk-air interface. 

To characterize this phenomenon, we develop a mechanical model that predicts hypocycloidal brittle fracture in adsorbed protein films subject to an in-plane, radial Marangoni pressure.

Using high speed imaging, we capture the early-time evolution of starburst fracture on aqueous beta-Lactoglobulin (bovine whey) protein solutions, and apply our model to measure the fracture energy of these protein films.