Hello!
I have a question about the pores in membranes.
Membranes made of nitrocellulose, PVDF, nylon and other polymers are widely used in laboratories for blotting, filtering, etc.
Almost any membrane has an inscription with the typical pore size, e.g. 0.2 um, 0.45 um and fey others.
If we take any of these membranes and analyze the surface with a scanning electron microscope, we will find a wide variety of shapes and sizes of individual pores. Thus, where does a specific number come from? Is it the mean pore size? If yes, what analytical method (BET? SEM? ...?) is typically used to determine the pore size in such membranes?
The attached image shows the surface of a nitrocellulose membrane with 0.45 um pore size declared by the manufacturer. The scale bar is 5 um. The pores seem far larger than 0.45 um, and it is a very typical case...
You may find this url relevant Dmitry Bagrov
https://wiki.anton-paar.com/en/pore-size-measurement/
For pores this size the most adequate method would be mercury porosimetry. You can look here for an introduction to the method:
https://wiki.anton-paar.com/en/mercury-intrusion-porosimetry-basics-measuring-pores-in-solids/
It explains for solid but you can use the same method for membranes.
Some of the methods that can be used are visual examination using scanning electron microscopy, porosimetry, mercury porosimetry, bubble pressure and gas transport method, gas–liquid equilibrium method (permporometry), thermoporometry, and rejection of simple uncharged solutes in hydraulic pressure-driven experiments
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