Streaming potential trials

I’ve tested several membrane types with the streaming potential apparatus in order to calculate zeta potential.  Here are the results:

All materials in the above chart have negative zeta potentials.  Pnc-Si seems to have the highest overall potential, followed by PES then cellulose.  Cellulose is prone to cracking and bursting at pressure above 7 PSI.  UV/ozone oxidation of pnc-Si does not increase the zeta potential, which is not what I would have expected.  PES falls in a range of zeta potentials as found in the literature as does cellulose.  I would have guessed before looking that cellulose would have a stronger zeta potential than PES because it is more hydrophilic, but perhaps these things are not really linked.

These measurements, however, were done using water from the Nalgene containers.  As it is a pressurized format, there may be some deposition of organics.  I’m in the process of repeating the data with clean salts.

Last week we hooked up the YES system and tried some initial APTES silanization.  On glass slides there was a contact angle change (0 degrees unmodified, 50 degrees w/ APTES).  I silanized a couple of pnc-Si membranes for streaming potential experiments and here are the initial results:

Now, the zeta potential for this one is obviously not positive, but it is lower than standard pnc-Si.  The guys from Adarza suggested that the silanization in the glass petri dishes was not very complete. Perhaps we’ve added a little amino to this membrane, enough to maybe reduce the zeta potential, but not enough to fully coat the membrane surface.

UPDATE:

Some of the newer results with clean Barnstead water:

These trends agree well with previous “dirty” water trials.

Also, the equations say there should be no dependance of active area on zeta potential.  Here is a comparison of pnc-Si zeta potential in 9 and 3 well formats (each well is about .1 x .1 mm):

There’s a pretty good amount of overlap here.  The 3x well is from the clean water results while the 9x well is from dirty and probably should be repeated if published.