The effect of vibration on liquid drop motion

The innate desire of mankind to understand himself and his environment drives him to advance technology that assists in learning about the natural world. This age-old passion, coupled with recent technological innovations in computer science and genetics, spurred development of myriad miniature fluidic devices that aid in efficient collection and analysis of biological and chemical data. The purpose of the first generation devices was to miniaturize, automate, and integrate operations of bench-top chemists on a planar chip. Many of these devices use a continuous flow paradigm, where a stream of inert liquid carrying plugs of reactants circulates through a channel network etched in a chip. But for numerous bench-scale batch processes, continuous flow designs do not properly mimic the real process. Two significant drawbacks are dispersion and accumulation of reactants within the channels. However, these and other problems can be remedied via channel-less corpuscular flow of liquids on a surface. This thesis discusses new methods to actuate droplet motion and integrate several unit operations on a chip to carry out truly miniaturized batchwise processes.; Liquid drops can migrate on surfaces possessing a gradient of adhesion; however, the critical drop size for mobility and speed is determined by the contact-angle hysteresis of the surface. One way to mitigate the effect of hysteresis is to induce a shape fluctuation in the drop using sinusoidal vibration. Asymmetric hysteresis in the surface free energy gradient rectifies the oscillatory inertial force, generating unidirectional drop motion. The magnitude of the rectification and the associated amplification of drop motion depend on the resonant modes of the drop, and the frequency and amplitude of the forcing function. Thus, drop motion can be controlled by modulating the vibration signal. However, a drawback of this technique is the inability to change drop direction because of the permanent, irreversible surface energy gradient.; This limitation is eliminated when a drop on a uniformly hydrophobic surface is subjected to a periodic asymmetric inertial force. Because the surface has no bias in wettability, drop direction depends only on the shape, frequency, and amplitude of the forcing signal, and the resonance modes of the drop.