In the production and construction process of water-based coatings, due to mechanical mixing, brush coating, roll coating, spraying and other operations, air is easily brought into the paint system to form bubbles. These bubbles are stabilized by the following two effects: Electrostatic action: The surfactant molecules in water-based coatings form directional micelles at the gas-liquid interface, with the hydrophilic end towards the water phase and the hydrophobic end towards the air, forming stable bubbles.
Marangoni effect: The presence of a surfactant causes the surface tension on the top of the bubble to be higher than on the sides of the bubble, creating a reverse flow of liquid that helps the bubble film remain stable.


1. Action mechanism of defoamer
The main function of the defoamer is to destroy the stability of the bubble and release the wrapped gas. Defoamer is usually composed of carrier oil, active solid particles and emulsifier, and its mechanism of action can be divided into the following three categories:


Bridging - dewetting action: When the permeability coefficient of the defoamer E > 0, the defoamer can enter the bubble film and form a bridge with the bubble double film. Due to the strong hydrophobicity of the surface of the active solid particles, the liquid on the film layer is dehumidified, resulting in the puncture of the bubble film and the bubble rupture. Carrier oil also has a dewetting effect. After entering the bubble film, oil droplets decompose and deform, resulting in dewetting.
Bridging and stretching action: After the oil droplets enter the bubble film layer to form the bridging effect, when the spread coefficient of carrier oil is > 0, the spread and diffusion of oil droplets will gradually stretch and thin the oil droplets until they break and cause the bubble to break. The action of silicone defoamer is mainly through the bridging and stretching mechanism.


Fluid entrain: When the permeability coefficient E < 0, the defoamant is repulsed to the Platonic channel near the bubble film, and enters the bubble film under the action of non-equilibrium capillary pressure. The carrier oil moves with the bubble film, causing the local bubble film to gradually thin and eventually break. The prerequisite for the fluid entrainment mechanism is that the carrier oil has a good spreading ability, that is, S > 0.


2. Classification of defoamer
Mineral oil defoamer: with mineral oil as the carrier, mainly used in matte and semi-gloss latex paint, the main mechanism of action is fluid entrain.


Silicone defoamer: silicone oil as the carrier, suitable for high-end coatings, the main role is bridging - stretching mechanism.


Molecular defoamer: non-ionic surfactants that destroy the bubble stabilization force at the molecular level, suitable for low viscosity, high gloss and low PVC paints and varnishes.


These mechanisms of action and classification explain how the defoamer interferes with and destroys the stability of bubbles through physical and chemical ways to achieve the purpose of defoaming. Understanding these mechanisms helps to select the best defoamer solution and provides a theoretical basis for the development of novel and highly effective defoamer