Fluidic Technologies
Laboratory

We developed a theoretical model and experimental demonstration of thin liquid film deformations due to a dielectric force distribution established by surface electrodes. We model the spatial electric field produced by a pair of parallel electrodes and use it to evaluate the stress on the interface through Maxwell stresses. By coupling this force with the Young-Laplace equation, we obtain the deformation of the interface. To validate our theory, we design an experimental setup which uses microfabricated electrodes to achieve spatial dielectrophoretic actuation of a thin liquid film, while providing measurements of microscale deformations through digital holographic microscopy. We characterize the deformation as a function of the electrode-pair geometry and film thickness, showing very good agreement with the model. Based on the insights from the characterization of the system, we pattern conductive lines of electrode pairs on the surface of a microfluidic chamber and demonstrate the ability to produce complex two-dimensional deformations. The films can remain in liquid form and be dynamically modulated between different configurations or polymerized to create solid structures with high surface quality.

We explore different physical mechanisms that could enable a fully reconfigurable microfluidic device - one which can change its shape, flow pattern or function dynamically, thus allowing researchers to ‘put their hands’ into a microscale experiment and enabling real-time decision making.

Electroosmotic flow is a well-established and efficient method for driving microchannel flows that relies on the interaction of an externally applied electric field with charge arising at the interface between the liquid and the channel walls. However, its relatively low velocities together with its dependence on the pH of the liquid severely limit its utility. Here, we experimentally demonstrate fast electroosmotic flow over microstructured superhydrophobic surfaces. By suspending the electrolyte in a Cassie-Baxter state over hierarchical surfaces, we create stable gas-liquid interfaces on which we induce charge through a gate electrode. We provide a detailed investigation and characterization of the electroosmotic velocity as a function of the surface geometry by utilizing particle tracking velocimetry in a microfluidic device, and show that the resulting electroosmotic velocity scales with the ratio of slip length to double-layer thickness. Compared to no-slip surfaces, we demonstrate an order of magnitude enhancement in velocity, and complete pH independency, enabling wider utility of EOF in manipulation of microscale flows.

We are developing a one-step rapid fabrication method that leverages the thermocapillary effect to shape thin liquid films into useful DOEs with sub-nanometeric surface roughness. Our system consists of a projection system, which illuminates any desired pattern onto the bottom of a fluidic chamber patterned with heat-absorbing pads. The heat induces surface tension gradients in the polymer-air interface, resulting in the polymer film deformation. The polymer is then photocured to yield a solid device.

We explore the ability to shape liquids into useful optical components by controlling surface tension.

The LiquiFab approach transforms a volume of liquid polymer into a desired 3D shape. In contrast to 3D printers, which create structures point by point, LiquiFab uses the natural physics of fluids in a zero-gravity environment to shape the entire liquid at once. Both full and hollow elements can be formed, characterized by extreme smoothness—surpassing the finish quality of conventional polishing methods. The resulting elements can be used independently or as building blocks for larger constructs.

FLUTE aims to find out if giant lenses and mirrors – the high-quality optical components needed for future large-aperture space telescopes – can be created from liquids in space.