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Many people use hydrophobic additives when making coatings, waterproofing, and ink formulations. So why does it make the coating hydrophobic? Core sentence: Hydrophobic additives migrate to the surface of the coating, reducing the surface energy of the coating and making it difficult for water to spread, resulting in the rolling effect of water droplets.

Common types of hydrophobic additives include wax (polyethylene wax, polypropylene wax), organosilicon (polydimethylsiloxane, silane, silicone resin), and fluorocarbon additives. They have a common feature: the molecule is divided into two segments, one segment is compatible with the resin system and anchored inside the coating; The other segment is a low surface energy hydrophobic chain segment that migrates and accumulates towards the air interface.

During the coating film-forming process, resin and pigment fillers form the main skeleton. Hydrophobic additives, due to their limited compatibility with resins, will spontaneously migrate to the outermost layer of the paint film. After the coating is cured, a large number of low surface energy functional groups (siloxane, long-chain alkane, fluorocarbon chain) are neatly arranged on the outermost surface of the coating. The surface tension of water is approximately 72mN/m. If the surface energy of the coating is lower than the surface tension of water, water cannot spread on the surface and shrinks into spherical water droplets, which is known as hydrophobicity and lotus effect.

Simple differentiation of different additives

1. Wax based hydrophobic additives: Long alkyl carbon chains migrate to the surface to form a thin layer of wax. Moderate ability to reduce surface energy, improve hydrophobicity and scratch resistance, low cost; The disadvantage is that a high amount of additives can easily affect gloss and interlayer adhesion.

2. Organic silicon hydrophobic additive: Si-O main chain, with side methyl groups arranged outward. Methyl has a low surface energy, good hydrophobic effect, and enhances smoothness and water resistance. Excessive use can lead to shrinkage and decreased recoating properties.

3. Fluorocarbon hydrophobic additives: Fluorocarbon chains have the lowest surface energy and the strongest hydrophobic effect. But it is expensive and difficult to regulate compatibility, and is mostly used for high-end stain resistant self-cleaning coatings.

Two key misconceptions

❌ Misconception 1: Hydrophobic additives do not “block and waterproof” coatings. It is not blocking pores, but mainly changing the surface interface characteristics. If the coating itself has pinholes or pores, water will still penetrate, but the surface will not be wetted.

Misconception 2: Adding more hydrophobicity is not necessarily better. Excessive addition can cause a large amount of additives to migrate to the surface, resulting in paint film loss of gloss, decreased interlayer adhesion, affecting recoating, and even surface adhesion and precipitation.

The core mechanism of hydrophobic additives to achieve hydrophobicity is the migration and enrichment towards the surface of the paint film during the film-forming stage, and the construction of a low surface energy molecular layer on the outer surface of the coating, reducing the spreading ability of water on the surface and achieving the hydrophobic effect of water droplets. It improves surface hydrophobicity and cannot replace resin based shielding and waterproof structures.

The core mechanism by which hydrophobic additives endow coatings with hydrophobic properties is interface migration and surface energy regulation. Hydrophobic additive molecules generally contain anchoring segments compatible with the matrix resin and low surface energy hydrophobic segments; During the film-forming and curing process of coatings, additives spontaneously migrate and accumulate towards the coating air interface due to limited compatibility, forming a low surface energy molecular layer on the surface of the coating. When the surface energy of the coating is significantly lower than the surface tension of water, liquid water is difficult to wet and spread on the coating surface, thus forming a hydrophobic effect of water droplets. Common hydrophobic additives include polyolefin wax, organosilicon, and fluorocarbon compounds, among which fluorocarbon chains have the lowest surface energy and the best hydrophobic effect. This type of additive mainly regulates the surface hydrophobicity, cannot seal the internal pores of the coating, and cannot replace the shielding and waterproof effect provided by the resin matrix; Excessive addition can easily cause defects such as paint film loss of gloss, poor recoating performance, and decreased interlayer adhesion.