Interfacial instability of thin films in soft microfluidic configurations actuated by electro-osmotic flow

Electro-osmotic flow is a commonly-used method to manipulate fluids in microdevices, often fabricated from soft materials like PDMS. We show that electro-osmotic flow systems may exhibit viscous-elastic interfacial instability. To provide insight on the underlying instability mechanism, we theoretically model an electro-osmotic flow interacting with an elastic substrate, and find that instability can result in asymmetric deformation, even for symmetric actuation. In addition to instability, the system nonlinearity, arising from the inverse dependence of the electro-osmotic actuation on the film thickness, results in hysteresis.