Microporous filtration membraneThe core filtration principle is * * physical screening * *, which achieves the separation effect of "intercepting impurities larger than the pore size and allowing fluids smaller than the pore size and small molecular substances to pass through" through the evenly distributed small pores on the membrane body. At the same time, auxiliary effects such as adsorption and bridging are used to improve the filtration accuracy.
1. Core mechanism: Physical screening, precise interception according to "size"
This is the most fundamental and main principle of microporous filtration membrane, similar to the screening process of a "sieve".
-The membrane structure determines the retention capacity: the pore size of microporous filtration membranes is usually between 0.02 μ m and 10 μ m, and the pore distribution is uniform. When the liquid or gas to be filtered flows through the membrane surface, particles larger than the membrane pore size (such as bacteria, sediment, suspended impurities) will be blocked on the surface or pore inlet of the membrane and cannot pass through; Water molecules, solvents, and small molecule solutes smaller than the pore size can smoothly pass through the membrane pores, achieving solid-liquid or gas-solid separation.
-The aperture directly matches the interception target: for example, a 0.22 μ m microporous filtration membrane can intercept the vast majority of bacteria (common bacterial sizes range from 0.5 μ m to 5 μ m) and is commonly used for drug sterilization in the pharmaceutical industry; 0.45 μ m membranes are commonly used to remove suspended particles and some microorganisms from water bodies, making them suitable for conventional water purification scenarios.
2. Auxiliary mechanism: adsorption and bridging, enhancing filtration effect
On the basis of physical screening, adsorption and bridging effects may occur in some scenarios to further improve filtration efficiency, especially for small particles close to the membrane pore size.
-Adsorption effect: Membrane materials such as polyvinylidene fluoride (PVDF) and nitrocellulose (NC) have weak charges or polar groups on their surfaces, which can adsorb small particles (such as colloids and suspended solids) in the system to be filtered through van der Waals forces, electrostatic forces, etc. Even if these particles are slightly smaller than the membrane pore size, they may still be adsorbed and trapped, reducing the risk of "leakage".
-Bridge function: When multiple small particles flow towards the membrane pores at the same time, they will "bridge" each other at the entrance of the membrane pores to form a small "filter cake layer". The particles that flow through will be further intercepted by this filter cake layer, which is equivalent to forming a "finer secondary filter" on the basis of the original membrane pore size, indirectly improving the filtration accuracy.
3. Key premise: Smooth membrane pores and filtration driving force
To effectively apply the above principles, two key prerequisites must be met, which are also the core of ensuring filtering effectiveness in practical applications.
-The membrane pores need to be kept unobstructed: if the impurity concentration in the filtration system is too high, a large number of particles will quickly block the membrane pores, leading to a decrease in filtration flux or even failure. Therefore, in practical use, it is often necessary to combine pre-treatment (such as removing large particles through coarse filtration), or choose microporous filtration membranes with "hydrophilicity" (reducing impurity adsorption) and "pollution resistance" materials.
-Reasonable driving force is required: Due to the small pore size of the microporous filtration membrane, the fluid will experience certain resistance when passing through, and external driving force is needed to push the fluid through the membrane. Common driving forces include pressure difference (such as positive pressure filtration, negative pressure suction filtration), gravity (suitable for low-speed filtration of low viscosity, large pore size membranes), among which pressure driving is a commonly used method in industry and laboratory, which can improve filtration speed and efficiency.
In conclusion,Microporous filtration membraneThe filtration process is centered around "physical screening", which achieves size separation through precise pore size design, and then optimizes the effect through adsorption and bridging. Finally, with the support of reasonable driving forces, it completes efficient and accurate separation tasks. This is also the core reason why it can be widely used in fields such as medicine, food, and environmental protection.