Thin-film approximations of the two-phase Stokes problem

Passing to the limit of small layer thickness in the two-phase Stokes problem we obtain when including only gravity (resp. surface tension) effects a strongly coupled parabolic system of second (resp. fourth) order. In the non-degenerate case we prove that the corresponding evolution problems are locally well-posed. For the gravity driven flow though, we have to assume that the less dense fluid lies on top of the less dense layer. Moreover, we show that the solutions converge exponentially fast towards a flat steady-state, which is uniquely determined by the volume of the two fluids, provided they are initially close to this rest state.