Yifan, sounds like a delta p problem, you might want to check the lengths,
widths, and depths of the respective channels. I worked on a H-channel (where
the vertical legs of the H were carrying separate liquids, and the center of the
H was wide and should have 0 velocity) gradient generator. I ran into a problem
where it would cross talk between the two legs. Sometimes in microfluidics
intuitive designs just won't work if you look at the numbers.

David Casale
R&D Engineer
www.maxlevy.com
Drexel University
Kim Group BAST Lab
Microfluidics.tripod.com

-----Original Message-----
From: Yifan Wu [mailto:fanclean@gmail.com]
Sent: Thursday, August 13, 2009 12:27 PM
To: General MEMS discussion
Subject: [mems-talk] Microfluidic problem

Dear all,

I was fabricating a microfluidic device which consists of glass substrate,
SU-8 channel (30um thick) and PDMS cover lid. The device has 2 inlets and 1
outlet. 2 inlet channel are 100um wide and once they mix into one outlet
channel, the channel shrink to 24 um. It is easy to suck the water from 2
inlet tubes into the channel. But after liquid reach the channel it is
impossible to suck it out from the outlet. The liquid can go from inlet to
inlet easily but not to outlet. Is this related to the hydrophobic property
of SU-8 and PDMS? How could I solve it? Thank you very much.

Yifan
University of Missouri