Spreading of a viscous fluid between an elastic sheet and a porous substrate

The dynamics of a thin film of viscous fluid spreading between an elastic sheet and a porous substrate are controlled by the deformation of the elastic sheet, the hydrostatic pressure gradient in the flow, and the viscous resistance of the flow in the gap and in the pores. We present experiments where fluid is injected between a rigid porous substrate and an overlying elastic sheet. First, fluid invades the pores, and after reaching a critical pressure, the elastic sheet is peeled and uplifted from the porous substrate forming a thin fluid-filled gap. Further injection causes the fluid front in the pores and the peeling front of the elastic sheet to advance radially. We study experimentally and theoretically the spreading dynamics in various regimes which are a function of the permeability of the porous substrate, bending rigidity of the elastic sheet, and injection rate.