Permeability of the lateral air flow through pillar-like nanostructures for microfluidic applications*

In many microfluidic devices represented as Lab-on-a-Chip, unwanted air can go inside during preparation processes. They can impede the flow of the device, and reduce the effectiveness of certain functions such as analysis and separation. To prevent this, we suggest a method for removing the air inside a channel using the nonwetting nanostructured substrate. In this concept, the permeability of the air passing between the nanostructures is very important. We prepared the pillar-like nanostructured substrate using the combination of dilute Ag-ink sintering and a metal-assisted chemical etching on a Si-wafer. The PDMS-based microchannel was fabricated and attached to the nanostructured substrate for experiments. By measuring the pressure change inside the initially pressurized microchannel, the permeability of air is compared with existing theories to analyze the results. Kozeny factors were determined, and the results were well explained with the previous studies. This work is to decide appropriate operating conditions for microfluidic applications, so the results are meaningful to suggest quantitative values for the appropriate operating pressure and expected degassing time in practical applications by evaluating the air permeability through the irregular nanostructures.