Fluid-structure interactions involving electrokinetic phenomena are increasingly relevant in microfluidics, biomedical systems, and soft robotics. One notable electrokinetic phenomenon is diffusioosmotic flow—the spontaneous movement of fluid along a stationary surface driven by a solute concentration gradient. In electrolyte solutions, diffusioosmotic flow arises from two effects: chemiosmosis, driven by osmotic pressure gradients within the electric double layer, and electroosmosis, which can be induced by a spontaneously generated electric field due to unequal ion diffusivities.
In this theoretical study, we analyze the fluid-structure interaction between diffusioosmotic flow of an electrolyte solution and a deformable microfluidic channel. We provide insight into the physical behavior of the system by developing a simplified one-dimensional model, in which a viscous film is confined between a rigid bottom surface and an elastic top substrate, modeled as a rigid plate connected to a linear spring. Considering a slender configuration and applying the lubrication approximation, we derive a set of two-way coupled governing equations describing the evolution of the fluidic film thickness and the solute concentration. Diffusioosmotic flow, driven by solute concentration differences at the edges, generates fluidic pressure acting on the plate, leading to fluid-structure interaction. Our theoretical predictions show that above a certain concentration gradient threshold, negative pressures induced by diffusioosmotic flow give rise to fluid-structure instability, causing the elastic top substrate to collapse onto the bottom surface.
