# In-Depth Study of Several Filter Membrane Pore Size Tests

First, bubble point method
1. Test principle: When the channel is blocked by liquid wetting agent, due to the surface tension of the wetting agent, if the hole is opened by gas at this time, it is necessary to apply a certain pressure to the gas, and the smaller the hole is, the more the hole is opened. The pressure required for the hole is greater. By comparing the relationship between the pressure and the gas flow rate of the porous material in the dry and wet state, the pore size distribution of the sample can be obtained by calculation according to a certain mathematical model.
2. Aperture test range: 20nm-500um
3. For the gas-liquid discharge method, since the gas-liquid interface tension is large, the smaller pore diameter can only be measured by increasing the gas pressure, but the high pressure is liable to cause a series of problems such as gas leakage, sample deformation, and pressure drop. The drawback of the bubble point method is that it is not suitable for measuring filter membrane materials with small pore sizes.

Second, suspension filtration
Test principle: the spherical particle suspension is used as the medium, and the sample to be tested is used for cross-flow filtration. The pore size distribution can be calculated by comparing the particle size distribution of the original suspension and the permeate, and the largest particle in the permeate is calculated. The diameter is the maximum pore size of the porous material.

Third, liquid and liquid elimination method
1. The test principle is similar to the bubble point method, and is also used to measure the pore throat, except that another liquid that is incompatible with the wetting agent is used instead of the gas as the cell opener;
2. Test principle: 10nm-200um
3. Test filter membrane material pore size advantages and disadvantages: Because the liquid-liquid interface tension is small, only a small pressure is required to measure a large aperture, so the pressure measurement error is large, and the optimal measurement range is 10 nm to 200 μm.

Bubble pressure method (gas-liquid displacement) pressure-aperture correspondence
Calculation formula: D=4γCosθ/△P