Diffusioosmotic flow or diffusioosmosis is the spontaneous movement of fluid adjacent to a surface, driven by a solute concentration gradient. With the advent of microfabrication technology in the 2000s, diffusioosmotic flow has become a common driving mechanism for fluid manipulation in microfluidic and lab-on-a-chip devices. Microfluidic configurations are often fabricated from soft materials such as poly(dimethylsiloxane) (PDMS). As a result, internal pressure gradients generated by diffusioosmotic flow to conserve mass induce elastic deformation of the channel walls, giving rise to fluid-structure interaction.

 

We study the low-Reynolds-number fluid-structure interaction between diffusioosmotic flow and a deformable microchannel using a combination of theoretical modeling and finite-element numerical simulations. This multidisciplinary problem brings together fluid mechanics, mass transfer, electrokinetics, and elasticity. Recently, we demonstrated that soft microfluidic systems driven by diffusioosmosis may exhibit fluid-structure instability. To elucidate the mechanism underlying this instability, we developed a theoretical model in which the deformable boundary is represented as a rigid plate connected to a linear spring. This reduced-order model captures the interaction between the flow and an elastic substrate, and predicts that above a critical solute concentration gradient, the negative pressures induced by diffusioosmotic flow lead to collapse of the elastic top substrate onto the bottom surface. We are now extending this model, originally focused solely on the temporal dynamics of the fluidic film thickness, to study the viscous-elastic interaction and the spatiotemporal evolution of the deformable walls of a soft microchannel driven by diffusioosmotic flow.

​​​