Facile design and fabrication of capillary valve for mixing using two‐step PDMS moulding

Abstract

The traditional capillary mixing using a closed channel and a mixing unit without the delay valve encounters problems of backflow and clogging. Here, the polydimethylsiloxane (PDMS) mixing channel with the facile delay valve and open surface design has been demonstrated using the two-step moulding for long-term-hydrophilic capillary-pumping. The triggering of delay valve before the mixing unit is controlled by the specific channel height calculated using capillary theory. It can eliminate the problems of backflow, clogging and bubble defect. Also, the channel height in an open channel is reduced to 150 μm compared to the close one of 250 μm by numerical analysis. The CO 2 -laser-ablated polymethylmethacrylate (PMMA) mother mould can avoid the complicated fabrication process using photolithography and SU8 mould. Using the unique two-step PDMS moulding method can greatly diminish the defect from the laser-ablated PMMA mould for a smoother surface. The naturally hydrophobic PDMS is modified using the polyethylene glycol and O 2 plasma treatment to solve the sticking problem and prolong the hydrophilicity up to 164 h and more which is tested in the contact angle aging measurement.