Abstract
This paper designed a micro fluidic chip containing passive micro valve to control flows in micro channel stopping and continuing flowing after specific time. It depends only on the physical energy, which is surface tension, to activate this chip operate sample loading, flow transfer, and flow switch correctly without any input power. According to Young’s Equation, flows in micro channel will encounter a negative pressure barrier when liquid meniscus goes through an abruptly increase of side wall angle. After that, hydro-gel which was UV solidified in side channel absorbs water and swells into main channel, pushes valve and restarts flow going. The gating time from flow stopping to reflowing is about 15s for prototype. The micro channel is fabricated by PDMS modeling with SU-8 mold, and then bonding this micro channel to a glass slide after surface plasma treatment. First, fabricate different depth of channel to find out whether gating time can varied with it or not, then prepare several portions of hydro-gel with different concentration to obtain better gating time. The swelling and UV light solidified property of hydro-gels is mainly from short chain gels, therefore the existence of long chain gels will reduce the expansion, refines whole time gating efficiency, and reduce the flow rate drop resulting from over swelling of hydro-gel furthermore.