In this post I show the sieving coefficients of simulations with a thin membrane, a thick membrane, or a no membrane case as they approach equilibrium. The simulations were carried out for 48 hours, and plotted for 1 hour time points. Both thin and thick membrane had the same pore distribution – monodisperse 10 nm…
Here is the most up to date figure that I’ve made to compare the simulated and experimental separation results. I went back through the x-ray crystals and remeasured the longest distances in the molecules. I used the radii to rerun the simulations and plotted them against protein and rhodamine diffusion data. Here are the results:…
In this post I will explain how I tried to use the 1D diffusion model to check the results we had in the Nature paper. Unfortunately I didn’t get the same results in the simulation and I present some ideas for the discrepancy. In the Nature paper we made simple small volume diffusion chambers and…
In this post I will show that the analytical 1D model of diffusion is similar to our 3D COMSOL model, with the exception that the times do not seem to line up. This is reasonable though since the 1D model does not take into account the non-membrane silicon pieces and enlarged volumes that occur in…
Using the same procedure as in the last post, I was able to simulate a 6um thick membrane with the same pore characteristics as the experimental pnc-Si membranes. Material diffuses more slowly through this membrane, but not as slowly as I expected. The following figure shoes the filtrate/retentate concentration ratios at 24 hours for a…
Follow up to this post. As a brief reminder, I have performed 3-D simulations of separations in large and small volume systems. I have defined an effective diffusion coefficient that takes into account the membrane hindrance and compared this to free diffusion. As the Deff/D0 ratio drops, this means the membrane has a higher impact…
This device was built similar to the device featured in the Burns(Zydney) 2000 J. Mem. Sci. paper. Our device seals in a SepCon formatted pnc-Si chip and allows 2 electrodes to be positioned by the chip. A feed line pressurizes the chip with saline, and the generated potential can be measured using the electrodes. The…
In the previous post it seems that the membrane pores do not significantly retard proteins and that the separation characteristics are due more to the slower diffusion coefficients of the proteins. However, in certain circumstances, the membrane may provide more of an effect. All of these experiments and simulations took place in a relatively large…
Tweaking simulation was not bringing it any closer to the experimental shown in the last post. This led me to try the experimental once more. I set up the same system and used 1:2 dilution of the standard protein mixture. I then homogenized the retentate and filtrate and ran 10 ul of each on a…
I’ve been attempting to simulate protein sieving using the COMSOL model. This first figure shows the comparison of the simulated separations to the actual results as determined by gel densitometry. The simulated separations tend to lag behind the experimental data for smaller proteins. This is surprising since the simulation is faster than experimental results for…