I have a PDMS microfluidic device with one channel (10mm X 5mmX 50 um) having an inlet (2mm diameter hole) and outlet (2mm diameter hole). I am trying to pass solutions through inlet and pulling out at the outlet with a syringe pump. I find a back flow at the outlet and air bubbles also. How can I avoid these air bubbles and back flow ?
Hello Sasank,
I attach a link to a guide by Elveflow that may provide some suggestions:
http://www.elveflow.com/microfluidic-tutorials/microfluidic-reviews-and-tutorials/air-bubbles-and-microfluidics/
My personal suggestion would be to try adding a 'bubble trap'. I only have experience with Diba's product:
http://www.dibaind.com/labware/omnifit-labware-filters-check-valves-bubble-traps/
I also usually follow your method of creating negative pressure at the outlet and found this to be better than creating a positive pressure at the inlet (I do this with a range of pumps: syringe, peristaltic and pressure pumps). However, could you try reversing the configuration and pushing? Do you have problems with bubbles at all flow rates?
RSC's blog 'Chips & Tips' may have some suggestions. Below is a link to a quite an interesting suggestion of purging the system with CO2 prior to liquid:
http://blogs.rsc.org/chipsandtips/2013/05/10/a-simple-effective-and-cheap-means-to-reduce-bubbles-in-microchannels/
Sorry I cannot give you a definitive answer.
Hope you find a solution.
Jules
The most simple solution to avoid air bubbles is to treat the device with oxygen plasma and de-gas in a vacuum desiccator. However, PDMS hydrophobically recovers within a few hours esp. when exposed to air. Pre-priming the channels with ethanol also helps.
This paper gives an in-depth discussion of bubble formation:
https://pdfs.semanticscholar.org/50fb/ce1ccd457488e0430f0782818dbd1cd13a19.pdf
If you can be flexible with your chip design, you may draw inspiration from a few of these papers:
http://pubs.rsc.org/en/Content/ArticleLanding/2010/LC/c005274d#!divAbstract
http://pubs.rsc.org/en/Content/ArticleLanding/2012/LC/c1lc20817a#!divAbstract
Best,
Jonathan
To prevent backpressure you may use a larger diameter tubing at the outlet with respect to the inlet.
Is their any criteria or correlation exists that can predict length of multichannel to avoid backflow...I have the same problem in cfd simulations at shorter lengths.
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