What are the commonly used measurement methods for microporous filtration membranes?

When we measure microporous filtration membranes, we usually use several main tools, such as optical microscopes, scanning electron microscopes (SEM) and transmission electron microscopes (TEM), etc. These are tools for visualizing and characterizing the membrane surface and structure, and can provide insights into the pore size, shape, distribution and overall morphology of membrane materials. There are many applications of such tools and related measurement methods. Here is a brief introduction.

1. The bubble point measurement method mainly determines the pore size and the minimum pore size corresponding to the pressure by measuring the pressure when the liquid or bubble begins to flow through the membrane, so as to provide information about the maximum pore size in the membrane, such as using a bubble point meter to apply increasing pressure to the membrane until bubbles emerge from the pores, and the pore size distribution data is determined by the pressure.

2. Capillary flow porosimetry, this method mainly measures the flow rate of non-wetting liquids through the membrane. By using different liquids with known surface tension, applying pressure according to the gradient to measure the flow rate of non-wetting liquids through the membrane, analyzing the flow characteristics (such as pressure, flow rate and liquid characteristics), etc., the pore size distribution data can be determined.

3. Mercury intrusion porosimetry, this technology measures the intrusion of mercury into the membrane pores under increasing pressure. By analyzing the volume of intruded mercury under different pressures, the pore size distribution, pore volume and specific surface area are determined. Since this type of technology can measure the intrusion or adsorption of fluid mercury (or including the use of other gases, etc.) under relatively precise controlled conditions, it is a relatively common method, especially in the measurement of relatively small micropores.

4. Gas adsorption (BET) Brunauer-Emmett-Teller method, commonly used to measure the specific surface area and pore size distribution of microporous membranes, measure the adsorption of gas (such as nitrogen) at different pressures, and use the BET equation to analyze the data to determine the paging data of membrane surface area and pore size distribution.

5. Scanning electron microscopy (SEM) method, using electron microscope to scan the membrane surface and cross section with high resolution, so as to obtain the morphology and structure of the membrane (including pore size and shape), combined with image analysis software, to analyze the microscopic image of the membrane, and obtain quantitative pore size, shape and distribution data. SEM can provide qualitative information about the microporous properties of the membrane.

6. Atomic force microscopy (AFM) method, AFM method is a high-resolution imaging technology, mainly using a sharp probe to scan the membrane surface, which can provide detailed information about the pore size and shape and surface roughness, and some can even measure the height of a single hole.

7. Laser diffraction method, laser diffraction is a technology that measures the scattering pattern generated when a laser beam passes through a particle suspension. By analyzing the diffraction pattern, the particle size distribution can be determined, thereby indirectly providing information about the pore size distribution of the membrane.

In short, there are many methods and techniques for measuring microporous membranes. Simply using one of them will have its limitations depending on the needs. Because different methods are suitable for different specific measurement items, in actual applications, multiple technologies should be combined for combined measurement. In this way, the pore structure and size distribution of the microporous filtration membrane and its content can be fully understood.