It seems plausible that you should place the chip inside a vacuum chamber, create vacuum and seal the chip inside there: vacuum causes the air bubbles to grow in size, thereby becoming more buoyant and thus moving towards the surface, the air inside them to be subsequently removed from the chamber.

Could you flush the channel with isopropanol or ethanol and then switch the feed medium to water/oil without trapping air bubbles? 

hello Farid and Pesch 

Thanks for the suggestion. I will try both. Much appreciated. 

You are welcome Sahana. Please let us know the outcome of your experiments.

hello,

I tried both the suggestions. But the problem is, my microfluidic chip has a storage chamber (not a continous design where I can collect drops)!

In these cases, It is very difficult for me to flush isopropanol and take it completely out of the system. I tried flushing with isopropanol and blow drying with nitrogen later, it seems a bit better.. but not good enough to remove the air bubbles.

With the vaccum chamber, My chip is a open end chip, therefore even if I vacuum desicate it, by the time I remove them and use it for my experiments, its a good enough time to loose all the vacuum..

This sounds like you would need to make the channel hydrophilic. Do you bond the PDMS using standard plasma or UV cleaning? This should give you hydrophilic surface. If you use the chip directly after bonding (up to some hours max) it should still be hydrophillic and there should be no problem with trapped air... I guess, have not tried it.

You can also coat the surface with some surfactant for hydrophilicity.

Something else I thought of when I wanted to add a reservoir is to add another outlet at the reservoir which is always closed, except when flushing the chip with Isoprop. By this, you can easily fill the channel with isoprop first, then fill it with your medium and flush the reservoir through the additional opening. Afterwards, close it and it is as if it would not be there! Is this something that could work?

Best

Georg

Hello Georg

Thanks for your feedback. Right now, I have to do some experiments with the design that I have been provided. But at later stages, what you suggested might be of great help. I use plasma for PDMS bonding with glass. I use it max 4 hours after it is treated with plasma ( I keep the plasma bonded chip at 95C for 3 hours). But flushing the PDMS with oil ( fluorophilic or hydrophobic) is helpful though which I tried recently.

Bubble traps can help reduce the bubbles in channel, if you can implement those in your channel. I also agree with the idea of using surfactant and flowing the liquid forcefully before the experiment. Check this article for bubble trap, it might be helpful: http://blogs.rsc.org/chipsandtips/2006/11/22/in-line-microfluidic-bubble-trap/