Whenever we agitate a liquid or pass through a gas, many bubbles are formed inside the surface area of the liquid. Some of the bubbles produced by the liquid quickly break up and disappear.Some liquids do not disappear, and more and more, the formation of foam.Foam is a dispersing system with a large number of bubbles dispersed in the liquid. The dispersing phase is gas and the continuous phase is liquid.The volume fraction of foaming liquid is very small, and the foam occupies a large volume.The gas is separated by a continuous liquid film, forming bubbles of varying sizes, which accumulate to form foam.

    Bubbler media, like surfactants, adsorb a layer of surfactant molecules in a directional arrangement on the surface of the bubble. When the concentration reaches a certain level, the bubble wall forms a solid film.Surfactant adsorbs on the gas-liquid interface, causing the surface tension of the liquid to decrease, thus increasing the gas-liquid interface, so that bubbles are less likely to merge.The relative density of the bubbles is much smaller than that of the liquid itself, and when the rising bubbles penetrate the liquid surface, a layer of surfactant molecules adsorb on the surface.Therefore, the bubble film with surfactant adsorbed in the air is not the same as the bubble film in solution. It contains two layers of surfactant molecules, forming a bimolecular film, and the adsorbed surfactant has a protective effect on the liquid film.Defoaming agent is to destroy and inhibit the formation of this film, defoaming agent into the bimolecular directional film of foam, destroy the mechanical balance of the directional film and achieve the bubble breaking effect.

    The defoamer must be insoluble in the foaming medium and can be dispersed into the foaming medium in the form of droplet, or droplet, or solid particle wrapping solid particle.The defoamer has lower surface tension than the foaming medium and can spontaneously enter the liquid film to break the bubble.

    Antifoam agent is easy to spread on the surface of the solution, automatically spread on the surface of the foam, will take away a layer of solution on the adjacent surface, so that the liquid film local thin, reach the critical thickness, liquid film rupture, foam destruction.The faster the defoaming agent spreads on the solution surface, the thinner the liquid film becomes, the faster the foam destruction rate is accelerated, and the defoaming effect is strengthened.Therefore, on the one hand, the reason for defoaming lies in the ease of spreading. The adsorbed defoaming agent molecule replaces the foaming agent molecule, forming a film with poor strength.At the same time, part of the solution adjacent to the surface layer is taken away in the spreading process, which thinns the liquid film of the foam, reduces the stability of the foam, and makes it easy to destroy.

    An excellent antifoaming agent must take into account both antifoaming and antifoaming effects, that is, it should not only destroy the foam quickly, but also prevent the formation of foam for a long time.The reason for this may be related to whether the critical micelle concentration of foaming agent (surfactant) in the solution exceeds.In excess solutions, defoaming agents (generally organic liquids) may be solubilized so that they lose their ability to spread on the surface and their defoaming effectiveness is greatly reduced.After a period of time, as the defoaming agent is gradually dissolved, the defoaming effect is weakened accordingly.