Convenient Method for Modifying Poly(dimethylsiloxane) To Be Airtight and Resistive against Absorption of Small Molecules

In this paper we present a simple and rapid method of modifying poly(dimethylsiloxane) (PDMS) surfaces with paraffin wax. PDMS that contains a layer of paraffin wax at its surface resists the absorption of hydrophobic molecules; we used fluorescence microscopy to confirm that paraffin-modified PDMS resists the absorption of rhodamine B. Furthermore, we demonstrated that microfluidic devices made from PDMS that contains a surface layer of paraffin wax prevent efficiently the transport of gas molecules through the bulk and into microchannels. We characterized the surface of PDMS that contains paraffin wax using the water contact angle, optical transmission, and X-ray photoelectron spectroscopy. We show that PDMS that contains paraffin wax can be substituted for native PDMS; specifically, we fabricated peristaltic valves in PDMS that contains paraffin wax, and the valves showed no degradation in performance after multiple open/close cycles. Finally, we show how to use PDMS that has been treated with paraffin wax as a mold for the fabrication of PDMS replicas; this approach avoids silanization of PDMS, which is a time-consuming step in soft lithography. The wax-modified PDMS channels also show performance superiro to that of bare PDMS in micellar electrokinetic chromatography for quantitative analysis.