Relationship between air permeability and water pressure resistance of microporous membrane

Air permeability and water pressure resistance of microporous membrane are one of the key factors reflecting its application performance. Generally, when the air permeability of microporous membrane increases, it may lead to a decrease in water pressure resistance. However, the relationship between them will also be affected by many factors. We can discuss the relationship and influence between them.

The so-called air permeability of membrane refers to its ability to allow air to pass or flow through its structure, that is, the measure of the permeability of membrane to air or gas, usually expressed in units such as liters/square meter/second (L/m²/s) or cubic feet/minute/square foot (CFM/ft²).
The water pressure resistance of microporous membrane refers to its ability to resist water penetration under a certain pressure, which is a measure of the ability of the membrane to block liquid water from passing through the barrier during the filtration process. The water pressure resistance of the membrane is usually expressed in units such as millimeters of water column (mmH2O), Pascals (Pa) or pounds per square inch (psi).

The relationship between the air permeability and water pressure resistance of microporous membranes is affected by many factors, such as the pore structure, surface characteristics and hydrophobicity/hydrophilicity of the membrane material:
1. The influence of pore structure. The size of the pore size will determine its air permeability and water pressure resistance data. Generally, the larger the pores and the stronger the connectivity, the higher the air permeability and the lower the water pressure resistance. On the other hand, the smaller and more tortuous the pores are, the lower the air permeability will be. It is more difficult for gas to pass through, which will cause the water pressure resistance to increase.
2. The surface characteristics of the membrane. If the surface of the microporous membrane is rough or the surface energy is low, it will affect the interaction between the membrane and air or water. The smooth surface with low surface energy tends to repel water, which will lead to higher water pressure resistance, but similar characteristics have a relatively small effect on air permeability.

3. The influence of the hydrophobicity and hydrophilicity of the membrane. First of all, the hydrophobic membrane repels water, and its special air permeability makes it easier for air to pass through the membrane. When the air permeability increases, its water pressure resistance will be lower. On the contrary, the hydrophilic membrane tends to retain water, so its air permeability is relatively low, but the water pressure resistance will become higher.
4. In addition to the above points, the specific relationship between air permeability and water pressure resistance may also vary depending on the membrane material, manufacturing process and intended application, because different membrane technologies, such as ePTFE (expanded polytetrafluoroethylene), polymer membranes or ceramic membranes, will show different changes between air permeability and water pressure resistance.

Based on the relationship and mutual influence between the two, microporous membrane manufacturers usually optimize the membrane's pore structure, surface properties and hydrophobic/hydrophilic properties to achieve the balance between air permeability and water pressure resistance required for specific applications, design special membrane materials or multilayer membranes to meet specific air permeability and water pressure resistance requirements, and provide customers with different needs for their applications.