one,
Gas Adsorption Method
1.
Test Principle:
The gas adsorption method measures pore volume by using low-temperature nitrogen adsorption, which helps determine the porosity of the material. This technique is effective for pores smaller than 200 nm but cannot characterize larger pores, making it unsuitable for many types of membranes that have larger pore structures.
2.
Pore Size Testing Range:
0.35–500 nm
3. Defects in Membrane Pore Size Testing:
This method can only test pores within the range of 0.35–500 nm, and it is not suitable for testing micron-sized pores. Additionally, it cannot distinguish between through-holes and blind holes, leading to significant errors when measuring the throat diameter of pores in membrane materials. This is especially critical as the throat diameter represents the narrowest point of the pore structure.
4. Method Test Schematic:
Second, Mercury Intrusion Method
1. Test Principle:
In this method, mercury is forced into a dried porous sample under external pressure, and the amount of mercury that enters the pores is measured as a function of pressure. This allows for the calculation of pore size distribution. However, this technique also has limitations, such as the inability to differentiate between sealed U-shaped pores and true through-pores, which reduces the reliability of the results. For very small pores (e.g., below 100 nm), extremely high pressures (20 MPa or more) are required, which may cause deformation or collapse of the membrane structure, leading to inaccurate measurements.
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2.
Aperture Test Range:
50 nm – 500 µm
3. Defects in Membrane Pore Size Testing:
(1) The pore size range tested is from 50 nm to 500 µm. To test smaller pores (below 100 nm), extremely high pressure (20 MPa or more) is needed, which is often too much for organic materials. Under such conditions, the pore structure may deform or even collapse, causing the measurement results to deviate significantly from theoretical values. Unlike the bubble point method, which applies lower pressure, this method is less suitable for delicate materials. (3) Like nitrogen adsorption, mercury intrusion also fails to distinguish between through-holes and blind holes, limiting its ability to accurately characterize pore throats.
4. Test Schematic
The liquid mercury is pressed into the pores of the sample, and the pore size invaded by mercury depends on the applied pressure. On the right, the sample tube is filled with mercury via a metal jacket and electrode cap (plate electrode). The mercury injection volume is then measured.
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Measurement of mercury discharge volume.
Three,
Bubble Point Method
Test Principle:
When a channel is blocked by a wetting agent, surface tension prevents gas from passing through. To open the pore, a certain pressure must be applied. The smaller the pore, the higher the pressure required. By comparing gas flow in dry and wet states, the pore size distribution can be calculated using a mathematical model.
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2.
Aperture Test Range:
20 nm – 500 µm
3.
For the gas-liquid displacement method,
Due to the high interfacial tension between gas and liquid, increasing gas pressure is necessary to measure smaller pores. However, this high pressure can lead to issues like gas leakage, sample deformation, and pressure drop. One major limitation of the bubble point method is that it is not ideal for measuring very small pore sizes in membrane materials.
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The drawback of the bubble point method is that it is not suitable for measuring small pore size membrane materials.
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4. Instrument Test Report Screenshot
5. Instrument Picture
Four,
Crossflow Filtration
1.
Test Principle:
This method uses a spherical particle suspension as a medium. The sample is subjected to cross-flow filtration, and the pore size distribution is determined by comparing the particle size distribution of the original suspension and the permeate. The diameter of particles in the permeate corresponds to the pore size of the membrane.
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Five,
Liquid-Liquid Displacement
1
.
Test Principle:
Similar to the bubble point method, this technique is used to measure pore throats, but instead of gas, an immiscible liquid is used as the displacing agent.
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2.
Test Principle: 10 nm – 200 µm
3. Advantages and Disadvantages of Membrane Pore Size Testing:
Because of the low interfacial tension between liquids, only a small pressure is needed to measure large pores, but this leads to larger measurement errors. The optimal measurement range is between 10 nm and 200 µm.
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Bubble Pressure Method (Gas-Liquid Displacement) - Pressure-Pore Diameter Relationship
According to the formula: D = 4 γCos θ / ΔP, the relationship between pressure and pore diameter is calculated as follows:
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