Track etched nanoparticle permeability
I used the transwell track etched membranes for these permeability experiments. I first looked at 5nm gold in 10mM KCl. After 24 hours the retentate and filtrate had just about equilibrated:
We can compare these scans to the stock 5nm stock solution and see that the height of the 525nm peak is related to the concentration.
| Sample | Height of 525 peak |
| 5nm stock | .0397 |
| polycarb retentate | .0196 |
| polycarb filtrate | .0138 |
| polyester retentate | .0184 |
| polyester filtrate | .0119 |
It looks from this that we’re not exactly at equilibrium because the filtrate peaks are a little lower than the retenates. If this did hit equilibrium, then the peaks would be less than half of the stock. The discrepancy could be related to loss.
10nm separations – 10nm particles go through both polyester and polycarbonate in 24 hours
30nm separation – 30nm particles go through both polyester and polycarbonate in 24 hours
What is the cutoff of these membranes? For a TE membrane to let 30nm particles through by diffusion over 24 hours, the pores must be quite large.
These are transwell devices, 400 um pores. We already knew from the TECAN data that the flux was superior (although the permeablity is lower). But the membranes have 400X more internal surface area than pnc-Si and so I was hoping to detect loss to the membrane. Unfortunately, there is nothing obvious.
Do you mean 400 nm pores? 400 um pores would be visible by eye, 400 nm pores are nearly visible with a good optical microscope. Either way, pores this large are in a totally different regime, so I understand why the flux is so good.
400 nm pores!
Yep, you can see these pores on our microscopes. Also keep in mind that there’s a porosity difference between these membranes – the PC is 10^8 pores/cm2 the PET is 4*10^6 pores/cm2.