Relaxation of a fluid-filled blister on a porous substrate

The relaxation dynamics of a fluid-filled blister between an elastic sheet and a porous substrate are controlled by the deformation of the elastic sheet, the viscous stresses in the pores, and the capillary pressure at the fluid-air interface. We present experiments where fluid is injected between a porous substrate and an elastic sheet. First, fluid invades the pores and subsequently, the elastic sheet is peeled and uplifted from the substrate resulting in a fluid-filled blister. Further injection causes both the fluid front in the pores and the fracture front of the blister to propagate radially. After injection is stopped, the fluid continues to advance into the pores as the elastic stresses in the overlying sheet drive drainage of the blister. We conduct experiments and develop a mathematical model to study the effects of blister size, permeability of the porous substrate, and bending stiffness of the elastic sheet on the relaxation dynamics. We find that the bending stiffness of the elastic sheet and the permeability of the substrate largely control the dynamics, but for thin sheets and low permeability substrates, the capillary pressure at the fluid-air interface significantly affects the dynamics.