Godin:Protocols/Multilayer PDMS

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Safety Safety goggles Nitrile gloves Lab coat Clean room gowning Fume hood Materials Valve and Microchannel masters Distilled water Ethanol Isopropanol Stereo microscope Scotch tape Pipette tip Tweezers Polystyrene dish Vacuum Oven Aluminum foil Scalpel Weighing dish Scale PDMS Godin:Protocols/Sonicator Godin:Protocols/Spin coater Godin:Protocols/Mask aligner Description This protocol details the fabrication of a 2 layer PDMS device, consisting of a valve layer (top) and channel layer (below). It is assumed that masters for respective layers have already been fabricated (see Godin:Protocols/SU-8 Master, Godin:Protocols/AZ Master). The idea is to modify the silicone elastomer base to curing agent ratio, thereby modifying PDMS elasticity. Valve Layer Mix PDMS 7:1 For most devices, 80g of PDMS is sufficient to produce reasonably-sized devices. Weigh 70g of silicone elastomer base on the scale using the weighing dish, then add 10g of curing agent. Make sure to maintain the 7:1 ratio; if too much is added, add more base as required. Use a pipette tip to mix the solution for 10 min under the fume hood. Blow dry the valve master with nitrogen, and place in a polystyrene dish. Use Scotch tape to fix the wafer at the center of the dish by taping all sides. We want to prevent the wafer from floating up, or PDMS from getting under the wafer. Close the dish with the lid. 30 min degass Place the dish in the vacuum chamber, and allow it to degass for 30 minutes, or until it stops bubbling. To prevent overflow, you may have to periodically break vacuum and allow some bubbles to escape. 12 min @ 80°C The dish is now placed in the oven for 12 min at 80°C. The idea is to partially cure the PDMS, so it's solid but still sticky. Let the PDMS cool for about an hour afterwards; this will facilitate the next step. Punch valve holes Cut out each device from the wafer. Be careful to avoid cutting near master features, as it will be reused for future devices. Use the 0.75 mm hole punch to make a hole at the valve inlet for each PDMS device. The stereo-microscope is great for finding your features. Keep the light arms at a low incidence angle with respect to the PDMS surface so the features stand out. Place your PDMS piece on a junk piece of PDMS so you can easily go through without damaging the punch, and keeping holes consistent. The PDMS should be fairly sticky, so do your best to make it smooth. Try to keep holes vertical. Cleaning Rinse devices thoroughly with distilled water, making sure the water goes through the valve hole. Next, sonicate for 5 min in each of these solutions: soapy water, deionised water, ethanol and isopropanol. Dry with nitrogen, store in a closed clean dish. Fluidic Layer Mix PDMS 20:1 30 min degass Spin coat 10 min @ 80°C Device Fabrication Alignment >2 hrs @ 80°C Punch fluidic holes Cleaning