Hi,

To make your microchannels superhydrophobic, you'll need both a micro/nanostructuration (for example grooves, posts, microhole arrays) with dimensions around a few tens of micrometers maximum, and an hydrophobic coating. To my knowledge you can't perform this modification once the microchannel is assembled ; you'll need to realize the structuration beforehand on your master mold, then coat it with silane or teflon either before or after assembly.

I agree with Mahdi, plasma is the best way, or SAM layer deposition if possible. 

Hi 

Actually PDMS is hydrophobic in nature even though might not uniformly hydrophobic through out of the whole microfluidic channel. 

According to my knowledge, silanization technique could make PDMS uniformly hydrophobic, while plasma treatment could in contrast make PDMS hydrophilic.

Indeed to make PDMS superhydrophobic you have to create micro even nano structures on the surface. I have never heard a surface energy treatment to make PDMS microfluidic channels superhydrophobic. So I am looking forward to the answer too. 

Good luch!

Dear Florent, Mahdi, Hassan, and Shuaizhong;

Thanks very much for you response and suggestions.