The following is a plot of rhodamine diffusion for the experimental system at various time point: In this figure, the rhodamine approaches equilibrium, as defined as a filtrate/retentate value of 1. The 9x well chips have a larger active area and quicker diffusion. I have performed simulations of this system using COMSOL, and in this…
Due to the discrepancies between the 1D model and experimental runs with rhodamine, I have switched over to using COMSOL to solve for a 3D model. In this system, 200×200 um membrane squares with a 45 degree etch separate the two wells. The top well is set up with .5 mol/m3 of rhodamine, and the bottom…
In order to further test the model, I’ve set up additional rhodamine diffusion assays. In each case, the setup is similar to the nanoparticle/protein/dna separations – 20 uL of .5 mM rhodamine on the top of a SepCon and 20 uL .1 M KCl on the bottom. Two different membrane geometries were used so far…
Frustration with the lack of agreement with experimental device has led me to check if the diffusion in the wells within the model is physically relavent. To do so I’ve solved a partial differential equation pertaining to a concentration of 1 on the left half of the system and a concentration of 0 on the…
In effort to understand the model, I have been studying simple diffusion experiments using rhodamine, a small molecule expected to experience little hindrance. The model currently expects a small molecule the size of rhodamine to reach equilibrium within 1.5 hours. In the following figure, the retentate is blue while the filtrate is green. I…
This is an update of my progress with the diffusion model. Sieving coefficients for standard setup (Renkin only) In this image there’s a strong sigmoidal curve for the 24 hour diffusion. However, the cutoff (~34nm) is higher than cutoffs found in experiments. The lower time curves have unexpected shapes. This may be due to…
In an effort to measure the effects of bsa adsorption on pnc-Si, I made some samples from SC 073 (a good wafer for separations) and with the help of Graham Marsh (Waugh Lab), looked at them using AFM. We did our first studies of the samples in water, just in case that drying somehow distorted…
Here is the analysis of the wafers used in the pressurized gold separations: SC 199 Stat Result Mean Equiv Diameter 17.84 nm Median Diameter 18.30 nm Porosity 2.2% Weighted Mean Diameter 20.81 nm 90% Diameter 26.64 nm Roundness .782 Separates 10 nm from 15 nm w225 Stat Result Mean Equiv Diameter 18.33 nm…
This previous post contrasted how gold could be separated by pressure in deionized water, but not by diffusion (w199). I checked up on that diffusion sample again after 6 days, and while the retentate had mostly evaporated, there was no gold within the remaining filtrate. As you may recall, there has been some discrepency with…
A paper by Munch (from Kodak), Zestar, and Anderson in J Mem Sci (1979) writes that charge has a big effect on albumin separations in track etched membranes. They show in their paper that they can make the theoretical sieving match the results better if they simply add the Debye length to the molecular radius…