Buckling as a Tool for Spatiotemporal Sensing in Micromechanical Fluidic Systems

Stimulus-responsive deformations in soft materials are central to emerging strategies in microscale sensing and actuation, yet translating such behaviors into confined fluidic environments remains a challenge. Here, we introduce a microfluidic platform integrating upright polydimethylsiloxane (PDMS) membranes, which buckle predictably in response to binary isopropanol–water mixtures. Static experiments reveal that the critical buckling concentration increases with membrane thickness, while the buckling wavelength remains invariant. Finite element simulations incorporating nonlinear swelling accurately capture both the onset and amplitude of buckling. Under dynamic conditions, we observe traveling buckling waves driven by propagating solvent fronts – a phenomenon governed by the coupled kinetics of swelling, diffusion, advection, and elastic instability. These soliton-like deformations serve as self-reporting signatures of local composition gradients. Our findings establish a paradigm for solvent detection based on geometry-controlled elastic instabilities, offering a robust platform for passive, label-free chemical sensing, programmable fluidic responses, and the design of soft robotic and logic-enabled microsystems.