All electrokinetic phenomena are connected by a form of the Helmholtz-Smoluchowski equation.  In the case of electroosmosis, the equation can be written as follows: where v is the velocity (in m/s) of water flow through the pores, epsilon the permittivity, E the electric field, zeta the zeta potential, and eta the viscosity.  Since we do…

During the past few weeks, I have been experimenting with different array setups for diffusion. I have been working with BSA, but I will move to APOBEC3G protein once the arrays Barrett designed are finished. All of the pnc-Si arrays used were treated with UV-ozone. Treating with UV-ozone cleans the surface and helps prevents the…

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….

Chris asked me to do some scans of samples last week but I didn’t have time to get to them.  I was able to scan them today since I was setting the AFM up for my class anyway. I took 1um square scans (512×512) at 1Hz for all samples.  The target and set point voltages…

Today I tried to pass 5 nm gold through three different membranes with similar cut-offs but distinct mean diameters and porosities.  All the samples I used were ozoned yesterday and tested for water permeability. Based on the absorbance measurements, it seems that the 5 nm Au passes through 582 and 558 but not the carbonized…

I tested four membranes with different porosities today, including one that had been carbonized.  Here are the pore size distributions with TEM micrographs. I ozone treated all the samples prior to running the experiments, including the carbonized sc 582.  I expected some of the carbon ring to oxidize, which TEM confirms: It would appear that…

Last week, I finished up an initial experiment to investigate whether pnc-Si membrane geometry affects cell morphology.  To do this, I used a mask with 2×2 arrays of different size squares and also samples with 4 slits of different lengths and widths.  A lot of the samples broke before I got the wafer, so this…

I did two tests using water straight out of the Barnstead and with water from the cleanroom in Hopeman.  I was able to maintain high permeability using the same membrane for at least three successive trials with both.  It looks like the culprit is the Nalgene container used to store the water.  For any sensitive…

Hi all! Above is an image of the bioreactor made from the square, 5-slit pnc-Si chip and a PDMS structure.  Fused-silica capillary tubings were inserted into the bioreactor to form the inlet and the outlet for the transfer of the cells into the lower compartment, which is made entirely out of PDMS.  Note that the…

I’ve become increasing suspicious of the membrane clogging during the hydraulic permeability experiments.  I ran an experiment where I took three fresh samples (sc 582) and pushed water through for 5, 10, and 20 minutes.  Ideally, the permeability would be the same for all three time points.  However, I observed a decrease at each increasing…