Study and applications of liquid behavior on microtextured solid surfaces

摘要

Engineering the behavior of liquids on solid surfaces has wide applications ranging from the design of water-repelling surfaces for daily use to fluid flow manipulation in lab on chip devices and inhibiting corrosion of machinery. Given the ubiquitous interaction of liquids with solids, these applications only represent a drop in the seemingly endless ocean of opportunities. Thus it is not surprising that researchers have been trying to decipher this phenomenon for several centuries now but the complexity of this multi-scale phenomenon has left much to be understood. Recent advances in micro/nano manufacturing have granted researchers an unprecedented ability to control surface texture and properties. This, combined with the fact that surface forces become increasingly important at small scale, makes it an opportune time to focus studies in the area. Understanding liquid-solid interaction and developing applications around the same has been a central theme of this thesis. In this work, I have explored the solid-liquid interaction at a fundamental level and developed a thermodynamic model of a liquid drop on a rough surface. The model is validated by several experimental observations from other researchers. Using the model, I have shown that the geometry of roughness features could play an important role in the determination of thermodynamic state of the liquid on the surface as well as characterization of solid surface. Further, I have used this understanding to predict wetting anisotropy on asymmetric sawtooth surface and demonstrated the same experimentally. I also demonstrate a passive cascadable microfluidic logic scheme. The design is centered around interfacial phenomena and does not require any external power and has no electronic components. The scheme could replace electronic controls in diagnostic systems leading to increased portability and reduced costs. It can also be used in environment harmful for silicon electronics. In another application, geometry based surface patterning is explored in creating wall less flow in microchannels. I have used the latter to add scalability to the passive cascadable logic scheme. Wall less flow could also provide tremendous increase in liquid-gas surface area and open up opportunities to develop liquid-gas reactions systems or possibly ???self-cleaning??? air-filters.