Surface structure modification and wettability control are very crucial for the advancement in microfluidic systems. The wettability control of the surface is achieved by depositing a Self-Assembled Monolayer (SAM) on the surface. The technology of SAM has been advanced by coating the selective interior regions of silicon wafer. This was accomplished using a mask wafer with open slots attached to define the areas that need to be coated. Besides the capability of controlling the wettability, structure modification such as controlling hole size leads to the magnification of the influence of surface tension force. As the size of the hole gets smaller, the surface tension could become a dominant force. This paper utilizes a unique approach to improve the water and air management at the cathode of a micro Direct Methanol Fuel Cell (DMFC). Both structure modification and local surface wettability control are utilized. A two-inch silicon wafer is formed of alternate strips of hydrophobic and hydrophilic zones with arrays of holes of different sizes. Water will be guided along the hydrophilic wetting zones with large hole openings; while the air goes into the cathode from the hydrophobic dry areas with smaller holes. This process ensures that the cathode is not flooded by water while air passes easily. The excess water at the cathode could be pumped back by a micro-pump to the anode so that the size of water storage will be minimized. Therefore, most of the storage reservoir space is used for the pure methanol, which enables the achievement of a high power density of the system. In this study, a silicon-based membrane is built accordingly to observe the water and air management. Images of the CCD camera showed clearly that the water drained from the big holes without blocking the air passages.

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