Wetting Induced Fluid Spread On Structured Surfaces At Micro Scale

Downsizing fluidic devices raises many problems, one being the rapid increase of pressure gradient that drives the fluid flow. In this context, surface induced fluid spread has attracted increasing interest. Here, we investigate experimentally how the surface properties such as structure profiles and wetting properties play a role in driving fluid spread. The structured surfaces with different structure profiles were fabricated by using nanosecond laser in line scanning mode on the Si substrates (typical hydrophilic material) and their wetting properties were adjusted by sputter-coating different material films with low surface energy. Then the spread of the red ink solution on the as-prepared surfaces was observed by microscopy. We found that in all cases with different structure profiles and wetting properties, the red ink solution spreads along the grooves on the structured surfaces. The relation of the spreading distance of the red ink solution in these grooves (z) with the spreading time (t) is in accord with the typical relation z = ct1/2. With the increase in both the width of the grooves and the wetting properties, the parameter c increases, indicating that the red ink solution spreads in the grooves with a higher velocity. These results indicate that the structured hydrophilic surfaces can offer certain drag force for fluid over them. Such drag force may provide an effective approach for fluid flow in microfluidic devices.In this paper, we do the following work:(1) Using nanosecond laser by line scanning mode to process silicon, we obtain different widths micro-groove in silicon surfaces. We investigate the width of the microchannel having inflence on flowing characteristics of the liquid.(2) We adopt magnetron control sputtering device by sputter-coating different material films with low surface energy.of silicon in the prepared silicon surface to study the wettability of different materials inflencing on the fluid flowing characteristics, the better wettability of the material obtained, the quicker liquid flows in micro-channel.(3) Using nanosecond laser by line scanning mode to process silicon, we get U-shaped micro-channel in the silicon surface. We investigate that once phenolphthalein comes across alkaline, the phenolphthalein will become red. We can find that not only the chemical reaction can also react in the micro-channel (or micro-reactor), but also the micro-reactor is with less reagents and the reaction is more easily controlled.