Surface-Mediated Fluid and Particulate Transport in Microchannels with Patterned Wettabilities

• Main Authors: Cheng-Ming Chiu, 邱振銘
• Other Authors: Hsien-Hung Wei
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/56040060902903686816

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 94 === Abstract The aim of this thesis is to examine the transports of fluids or particles in microchannels with non-uniform wettabilities. We utilize the PDMS-based microfabrication techniques to fabricate microchannels. With the aid of the techniques developed by our group, we can selectively modify surface properties of a microchannel for our study. There are two parts in this thesis. In the first part, we examine the behaviors of a liquid in a T-shape microchannel that has a hydrophilic/hydrophobic contrast between the main and branch channels. We measure the hydrostatic pressure (through the liquid height), the minimum driving force required for the water to enter the hydrophobic branch, to characterize the effect of the wettability on transporting the liquid in the channel. It is also found that the smaller the channel width, the greater the liquid height. We also employ the Young-Laplace equation to explain the underlying force balance, and find an excellent agreement between experiment and theory. This research can be applied to develop “microvalves” for controlling the fluid motion using hydrophilic/hydrophobic differences. The second part of the thesis is to examine the motions of oil drops in a bifurcating microchannel with hydrophilic and hydrophobic branches. We find that the drops can move towards the hydrophilic end due to the difference in surface-slip effects. The behaviors of the drop movements, however, can change at different applied flow rates. This is caused by interactions between surface effects and other hydrodynamic influences. We devise a scaling analysis to estimate the orders of magnitudes for relevant effects. The analysis also provides a rationale for explaining our observations. This research has potential applications in separating particles with differences in their affinities to the channel surfaces.