Defoaming Principle of Defoamer
Generally speaking, defoaming can be divided into four processes: the defoamer adsorbed to the surface of the bubble membrane; the defoamer penetrated into the surface of the bubble membrane; the defoamer diffused on the surface of the bubble membrane and absorbed surfactants; and the defoaming was caused by the unbalanced surface tension of the bubble membrane wall.
(1) the bubble breaking agent penetrated into the bubble wall through adsorption of foam and surface tension. Thereafter, the surface tension diffuses the defoamer on the surface of the bubble membrane, making the membrane wall thinner and the bubble burst. The infiltration coefficient E and diffusion coefficient S of defoamer are respectively
Infiltration coefficient E=ow+a-00>0
The diffusion coefficient S = awGi-00 > 0_w-surface tension of membrane wall;
_ 0 - surface tension of defoamer;
_-interfacial tension between membrane wall and defoamer.
Infiltration coefficient E and expansion coefficient S of different Defoamers in Waterborne Coatings
(2) Antifoaming agents and foaming substances in coatings are adsorbed on the bubbles together. The surface tension of the bubble wall decreases and the membrane wall becomes thinner, leading to damage. So the foam becomes unstable, and the upper surface disappears.
(3) Defoaming agent is adsorbed on the surface of bubbles in the coating. After the bubbles adsorb each other, a big bubble is formed at the adsorption interface. The increase of buoyancy accelerates the rising speed of bubbles in coatings and promotes defoaming.
(4) The infiltration expansion coefficient of the theoretical surface interfacial tension of the bubble wall viscoelasticity of defoamer has a corresponding relationship with the defoaming effect, but in fact there are still undetermined types. For example, in the paint with high emulsion concentration, the surface tension of the coating is similar to the surface tension of the added defoamer. Even if the defoaming agent is added to the coating, the change of surface tension is very small, so the theory of bubble breaking can not be explained. However, although the surface tension of the coating hardly changes, the length of the sheet decreases greatly due to the addition of defoamer. Therefore, compared with metal soap and paraffin defoamer, silicone and composite silicone defoamer have smaller plate length and less surface elasticity on the surface of foam film wall, so it is easy to defoaming.
The results show that when the interfacial activator is added to acrylate coatings, the anionic surfactant is more foaming than the non-ionic surfactant, and it is not easy to defoam. This phenomenon is due to the pushing effect of the liquid on the bubble wall, resulting in the enhancement of the binding force and hydrophilicity of the molecules in the adsorption layer of the liquid. Moreover, the stabilization of bubbles is achieved by the charge action on the wall of the bubble membrane. Therefore, compared with non-ionic, the coating is not easy to defoam after adding anionic interfacial activator with strong charge. At the same time, metal soap and paraffin defoamers have better effect in coatings with non-ionic interfacial activator, but not in coatings with anionic interfacial activator. However, silicone and composite silicone defoamers not only have good effect on adding non-ionic interfacial activator, but also have significant defoaming effect on coatings with anionic interfacial activator. Because of the different kinds of defoamers, the ion types of anionic surfactants related to foaming factors have different choices. Therefore, compared with metal soap and paraffin defoamers, silicone and composite silicone defoamers, no matter what kind of interfacial activator is added in the coating, their defoaming effect is very good.
Originality: Old Paint Workers