The pore size distribution of ultrafiltration membrane material can be accurately measured by liquid - liquid replacement method

The method to test the pore size distribution of the ultrafiltration membrane is mainly liquid-liquid replacement method. Other orifice methods such as capillary flow method (also known as bubble point method, bubble pressure method, gas-liquid method), BET method, mercury injection method, electron microscopy are not applicable or have great limitations. The basic principle of capillary flow method is similar to that of liquid-liquid replacement method, both of which firstly wet the ultrafiltration membrane fully with a wetting agent, and then use compressed gas or another liquid that is not soluble with the wetting agent to push out the wetting agent and open the membrane pore. Among them, the smaller the aperture is, the greater the opening pressure is required, that is, the aperture is inversely proportional to the opening pressure, and the aperture can be calculated according to the interfacial tension of the opening pressure and the wetting agent. As the interfacial tension between the two liquids is far less than that of the gas-liquid interfacial tension, the capillary flow method is generally not suitable for measuring the pore diameter below 100nm. Although the aperture under 10nm can be measured as long as the test pressure is increased by 10 times, it is not feasible in practice. High pressure test not only lead to a difficult sealing, the pore gas resistance is high, the gas is used up big, big measurement error, and the strength of the sample put forward very high requirements, such as measuring 10 nm aperture required test pressure at least 50 kg, such high enough to cause the deformation of the sample or even damaged, and most of the ultrafiltration membrane is a soft polymer material.

Relevant knowledge can be found in chapters 2.2 and 2.3 of the literature "new carbon materials, 2014, 29(6): 409-418." Literature "Separation and Purification Technology, 2010, 70(3): 314-319"

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