|dc.description.abstract||Microfluidics has been grown up very fast recently, and widely used in biomedical and chemical analysis, and precision machinery lubrication. Microfluidic devices utilize microfabrication to minimize thier size, which can reduce the amount of test samples and reagents, enhance the accuracy of detection. The droplet-based microfluidic device is one of the promising technologies. The droplet can be driven by pressure difference, electro-wetting, capillary force, chemical gradient, thermophoresis, photopheresis and so on. Among these, the capillary force or the use of surface roughness changes has the advantage of simple operation and simple manufacturing process. However, most of the literatures only demonstrate the feasibility of water movement between two discrete surfaces with different roughnesses. In this study, we use metal assisted chemical etching to make nano porous silicon structure with continuous change in the surface roughness and investigate the drops movement on the surface.
Porous silicon structure has large surface to volume ratio Metal assisted chemical etching process is an simple and cost effective way to make porous silicon. In this research, we deposit platinum films and use thermal annealing to make nano particles for the following metal assisted chemical etching. The corresponding nano structures can be made by adjusting different thickness of platinum films and different etching times. The relationship between different thickness of platinum films and etching times is investigated. The contact angle and hysteresis are measured to study the wettability of the porous surfaces. Different metal thickness is made by steady pulling the sample out of the etchant, that is then annealed and etched to produce porous structural with continuous structure size gradients. The results show that the driving force given by continuous porous structural gradients is very small, and is unable to drive the liquid drops. On the other hand, we find that there is a different hysteresis between the structural gradients on the two sides from the contact angles measurements of the inclined surface. Finally, we use squalane to test the capillary motion on the surface, which shown that squalane will move further toward the area with smaller pore structures.||en_US|