Contact Line Stability and “Undercompressive Shocks” in Driven Thin Film Flow

We present new experimental results for films driven by a thermal gradient with an opposing gravitational force. When the gravitational effect becomes non-negligible, the advancing front produces a very large capillary ridge which shows a remarkable tendency to remain stable. This phenomenon can be explained by new mathematical results for a lubrication model of the experiment. The advancing front evolves into an ``undercompressive'' capillary shock structure which is stable to contact line perturbations, unlike typical capillary ridges in driven film flows.