Buckling at the Fluid - Soft Solid Interface; A Means for Advanced Functionality within Soft Materials

Soft materials and compliant structures often undergo significant deformation without failure, a unique feature making them distinct from classical rigid materials. These substantial deformations provide a means for faster or more energy efficient deformations, which can be achieved by taking advantage of elastic instabilities. We intend to utilize structural instabilities to generate advanced functionality within soft materials. In particular, we use the buckling of thin, flexible plates to control or enhance the flow of fluid in a micro channel. The buckling deformation is created or altered via two different stimuli, first a mechanical strain and then an electrical signal. We investigate the behavior of each system under different conditions experimentally, numerically, or theoretically.

We also show that the coupled interaction between fluid and the soft film plays a critical role in the shape of deformation and consequently in the functionality of the mechanism.

We first embed a buckled thin film in a fluid channel within a soft device. By applying a mechanical strain to the device, we show both experimentally and numerically that the height of the buckled film changes accordingly as does the flow rate. We then offer an analytical solution by extending the classical lubrication theory to higher-order terms as a means to more accurately describe the flow in a channel with a buckled thin film, and in general, the flow in channels with any constrictions provided the Reynolds number is low.

Next, we use an electrical signal to make a confined dielectric film undergo out-of-plane buckling deformation. The thin film is sandwiched between two flexible electrodes and the mechanism is implemented in a microfluidic device to pump the fluid into a micro channel. We show that the critical buckling voltage at which the thin film buckles out of the plane is mainly a function of voltage while the shape of deformation and so the functionality of this mechanism depend considerably on the applied boundary conditions. Finally, we enhance the fluid-soft structure response of the actuating mechanism by substituting flexible electrodes with fluid electrodes, resulting in a significant increase in the actuation frequency as well as a reduction in the critical buckling voltage.