The most commonly reported technique in the literature to measure pore size is by SEM. However, I am doubtful regarding the accuracy of this technique for various reasons, the primary one being, the obtained nano fibers are mostly randomly oriented (not criss cross). They are deposited on top of each other randomly, hence dont have a constant spacing (pore) between the fibers as can be seen in the attached picture.
Has any one been able to successfully measure their pore size using an alternative technique? Perhaps something like size exclusion chromatography or positron annihilation spectrometery?
Dear Aisha,
welcome,
After inspecting your picture mesh, i would propose to define precisely what is meant by pores. Your structure can best described by multilayer network of wires laid on each other in a random manner. So, One can better speak from multiple layers of wires. Describing each single layer of wires and then stacking them on the top of each other one gets the whole structure.
One may define pores with different depths. The darkest pore will be that one with the greatest depth among the mesh.
So you can determine the pores by an optical method depending on the degree of the gray of the pixels. Assuming that the pixel intensity at a position x,y is P(x,y), then the pore will be that area where P(x,Y) smaller than certain threshold value Pth. Varying Pth one can classify the pores with different depths.
Best wishes
Dear Aisha,
welcome,
After inspecting your picture mesh, i would propose to define precisely what is meant by pores. Your structure can best described by multilayer network of wires laid on each other in a random manner. So, One can better speak from multiple layers of wires. Describing each single layer of wires and then stacking them on the top of each other one gets the whole structure.
One may define pores with different depths. The darkest pore will be that one with the greatest depth among the mesh.
So you can determine the pores by an optical method depending on the degree of the gray of the pixels. Assuming that the pixel intensity at a position x,y is P(x,y), then the pore will be that area where P(x,Y) smaller than certain threshold value Pth. Varying Pth one can classify the pores with different depths.
Best wishes
I think we need more information. What are you actually trying to characterize? Scientifically, this must be defined to next determine what types of techniques may be applicable. The key is first formulating the right question, then you can research to possible solutions or techniques which may aid you.
As noted, the picture you provided shows a wide range of layering and opening sizes (commonly seen in "mesh"). SEM would only provide a very general physical description. What other information do you need? Define your goal. Is your goal to characterize the amount of "open" area in the material? Or maybe you need a method of permeability determination ? Once you specify the goal, then use a key word search on the web to find books, articles and papers which address your interest to find solutions.
Dear Tanvir,
Micro CT can be used to analyze pore size distribution. Please check: https://www.bruker.com/products/microtomography/academy/2015/pore-size-distribution.html
Regards,
Fatih.
I am not aware of any direct measurement techniques which could be applied directly to your problem. That being said, if you don't need to map the pores and just want to calculate the average porosity of the film then may I suggest using a volumetric approach.
One of the mothods to do it would be to cast your film in resin of known density and then do an X-ray tomography. This will allow you to visualize the structure in 3d and hence, determine the average pore size. Alternately, just calculate the desnity difference using Archimedes principle for an identical resin block without the mesh with that of the mesh. The difference in density (accounting for fibers) is the pore volume.
Disclaimer: These methods will only be considered accurate if the mesh geometry/morphology is reproducible in your experiments.
„A CFP-1100-AI capillary flow porometer (PMI Porous Materials Int. USA) was used in this study to measure the pore size. Galwick with a defined surface tension of 21 dynes cm−1 (PMI Porous Materials Int. USA) was used as the wetting agent for porometry measurements. Electrospun fibrous scaffolds were cut into 3×3 cm2 squares and then soaked into the wetting agent. The soaked scaffolds were placed in adapting pan and sealed with O-rings for porometry measurement.”
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0112885
”Pore size of the nanofibrous membrane was measured by capillary flow porometry (PMI CFP-1100-AI, Porous Materials, Inc., Ithaca, NY, USA) using a wetting agent of 21 dynes/cm surface tension from four samples with three independent measurements for each sample.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3310718/
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