The field of microfluidics involves the ability to manipulate small volumes of fluid (typically 10's of nanoliters) through small channels (diameters of 10's to 100's of microns). The main application of microfluidics to date has been in Lab on a Chip (LOC). The term Lab on a Chip implies that all of the analyses performed in a standard laboratory are consolidated onto a single chip device. This allows for: the use of less sample volume and reagents, improved separations, lower costs, shorter analysis times, and smaller footprints of analyzers. Recently there has also been a growing interest in the ability to manipulate small volumes of fluids (particularly colored ones) in the displays industry. Here, the ability to precisely control the fluids can be leveraged into making a highly reflective display.
In both LOC and display applications it is imperative to be able to move the fluids reliably within the device. To date the dominant approach in microfluidics is to create a solid channel and flow the fluid through it using an external application of pressure. While this approach has proven to be very reliable it is not easily reconfigurable. If any change in the fluid path is desired a new channel configuration must be fabricated. The most robust approach to microfluidics leading to the widest range of applications would be one where fluid shape and/or position could be manipulated reversibly such that the same chip area could be utilized for a variety of fluidic functions.
Various electrical approaches have been demonstrated to have the capability of manipulating fluid shape. This behavior of electrically manipulating a bulk fluid is commonly referred to as electrofluidics. To date, none of the electrofluidic approaches have shown the ability to maintain fluid shape after the electrical stimulus has been removed. This is a major issue as constant application of electrical stimulus causes high power consumption, increases the complexity of the drive electrodes and electronics, can interfere with other processes such as electrical separations, and can reduce device lifetime.
Presented in this dissertation is the first platform capable of electrical reconfiguration of fluid shapes and paths, while maintaining those shapes even after the electrical stimulus is removed. The platform utilizes local increases in Laplace pressure to act as barriers to free fluidic flow, and has thus been given the title ‘Laplace barriers'. The physics and performance of Laplace barriers is presented using theoretical equations, experimental results, and dynamic numerical modeling. The various parameters of Laplace barriers are also optimized to show that a platform can be achieved with >60% open channel area, >5cm/s fluid transport, and for display applications with >80% reflectance and ~50:1 contrast ratio. Finally, a demonstration device utilizing Laplace barriers is presented, providing one example of how Laplace barriers can be used for practical applications.