How to judge and test the hydrophobicity of microporous membranes

To discuss the hydrophobicity of microporous membranes, we must first know the concept of hydrophobicity. The so-called hydrophobicity is a term used to describe the physical properties of substances or materials that repel water or tend to be unreactive or insoluble in water. The characteristics of hydrophobic substances are the repulsive force generated by the non-polar nature of hydrophobic materials, that is, the interaction between hydrophobic materials and polar water molecules. The intermolecular forces produce a hydrophobic effect and tend to form hydrogen bonds with each other rather than with hydrophobic substances, which causes the hydrophobic materials to aggregate or separate in the presence of water.

Based on the above characteristics, microporous membranes also exhibit varying degrees of hydrophobicity, depending on the materials used in their construction and the specific surface treatments applied. By hydrophobicity we mean the ability of a material to repel water or resist wetting. In practical applications, in order to effectively utilize this property of hydrophobic membranes, hydrophobic microporous membranes are designed, mainly made of materials that naturally repel water, such as polytetrafluoroethylene (PTFE), polypropylene (PP) or polyvinylidene fluoride (PVDF). These membranes are carefully designed to prevent water from passing through while allowing gas or other non-aqueous substances to pass through.

When selecting a microporous membrane for a specific application, it is important to consider the hydrophobicity level of the required membrane according to the intended use, so as to select a membrane with appropriate hydrophobicity to ensure optimal performance and efficiency during filtration or separation. It is necessary to design some methods for testing hydrophobicity. The commonly used methods for judging and testing the hydrophobicity of microporous membranes are as follows:
1. Contact angle measurement method, which is a widely used technique for evaluating the hydrophobicity of the surface of a membrane (including microporous membranes). The larger the contact angle, such as greater than 90 degrees or more, the stronger the hydrophobicity. The contact angle goniometer is usually used to measure the angle at which a water drop contacts the membrane surface.
2. Water inlet pressure test method. The water inlet pressure test of the membrane is mainly to determine the pressure of liquid (usually water) penetrating the microporous membrane. Hydrophobic membranes have higher water inlet pressure due to their repulsion of water, which also shows that they have anti-wetting and anti-liquid penetration properties.
3. Bubble point test method. The bubble point test measures the pressure of bubbles passing through the membrane pores when the membrane is wetted by liquid. Since hydrophobic membranes will have higher bubble points, they will also show their resistance to wetting and liquid intrusion.
4. Dye penetration test method. In this test, a colored dye solution is applied to one side of the membrane and the appearance of the dye on the other side is observed. Since hydrophobic membranes resist the penetration of dyes, the color change on both sides indicates the hydrophobicity.
5. Wettability test method. The wettability test method mainly observes the changes in the behavior of liquid (usually water) on the membrane surface. Since hydrophobic membranes will show the beading or repulsion of liquids, hydrophilic membranes will show the diffusion and absorption of liquids.
6. Flow rate measurement method. The hydrophobicity of liquids can also be reflected by the flow rate of liquids through the membrane. Compared with hydrophilic membranes, hydrophobic membranes usually have lower aqueous solution flow rates because they are anti-wetting.
7. Surface energy calculation method. Surface energy calculation can provide insight into the hydrophobicity of the membrane. Lower surface energy values indicate higher hydrophobicity because hydrophobic materials tend to have lower surface energy.
8. Chemical resistance test method. Testing the resistance of the membrane to various chemicals (including water and organic solvents) also helps to measure its hydrophobicity because hydrophobic membranes will show minimal swelling or degradation when exposed to liquids.

The above summarizes the methods used to measure the hydrophobicity of microporous membranes. We can use these methods in a comprehensive and diverse way to effectively evaluate and judge the hydrophobicity of microporous membranes and select the most suitable microporous membrane according to our specific filtration requirements.