Capillary Stop Valve Design with Modified PDMS

摘要

This paper describes a new capillary stop valve sealed with a modified polydimethylsiloxane (PDMS) cover. The valve is based on the control of the capillary burst pressure and uses the surface tension as a driving force which can be adjusted by the contact angle of the modified hydrophilic PDMS cover. The capillary valve and the capillary channel are fabricated on a silicon wafer and then bonded with a modified PDMS cover to produce the proposed device. The key characteristic of the proposed device is the adjustment of the contact angle of the modified PDMS to effectively operate the capillary action of the channel and the stop valve. The polydimethylsiloxane-ethylene oxide polymer (PDMS-b-PEO) is utilized in this work as a surfactant additive to the PDMS base and the curing agent mixture during the polymerization to create a hydrophilic PEO-PDMS elastomer. The contact angle of the fabricated PEO-PDMS can be adjusted from 80.9° to 21.5° with different mixing ratios. The concentrations of PDMS-b-PEO (PEO) accepted for our application are from 0.2% to 0.4%, and the contact angles of the PEO-PDMS are from 80.9° to 58.5°, which are the conditions needed to make the capillary channel and valve function efficiently in the testing device. The experimental results show that the flow velocity and stop valve property can be achieved in a large range by adjusting the contact angle of PEO-PDMS. This new stop valve in the capillary system, which is bonded with a PEO-PDMS cover, can be applied in numerous microfluidic devices and pumpless fluidic actuation mechanisms. It is an ideal design for cost-effective diagnostic tools and other biomedical applications.