Hi,
I am running a experiment which is basically a micromixer. The channel
itself is cast from PDMS on a mold of SU-8 on Si-Wafer. The two
solutions that I use in the channel to mix are
a) Phenolpthalein (0.03mol/litre) in Ethanol
b) NaOH (0.3mol/litre) mixed with a littel DI water and then Ethanol
is added to it.

The two solutions are pumped into the two inlets which evetually
converge inside the channel. On the NaOH side of the channel, after
running the solutions for about an hour or so, I see black deposits on
the PDMS. I am not sure what this is. Any suggestions to solve this
problem?

Thanks in advance

Vishwa