Foaming and defoaming
First, foaming
A foam is a system in which many bubbles are separated by a liquid phase, that is, a dispersion in which a gas is dispersed in a liquid. The gas is the dispersed phase (discontinuous phase) and the liquid phase is the dispersion medium (continuous phase). Since the density of the gas and the liquid differ greatly, the bubbles in the liquid always rise to the liquid surface very quickly, forming a bubble aggregate which is separated from the air by a liquid film composed of a small liquid, that is, a so-called foam.
Pure liquids do not form stable foams, such as pure water. Only a suitable surface contact can be added to form a stable foam. The foaming property is a so-called foaming agent.
Foaming performance includes two aspects of "bubble force" and "foam stability". The former refers to the difficulty of foam formation and the amount of foam generated. The latter refers to the persistence of foam generation - the difficulty of defoaming, that is, the length of foam "life".
The process of foam destruction is mainly a process in which the liquid film separating the gas is thickened and thinned until it is broken. Therefore, the stability of the bubble is mainly determined by the speed of liquid discharge and the strength of the liquid film. The main factors affecting the stability of the foam are the factors affecting the thickness of the liquid film and the strength of the surface film. These factors mainly include surface tension, surface viscosity, solution viscosity, and "repair" effect of surface tension. Generally, the larger molecule has stronger intermolecular interaction, and the foaming stability formed by the aqueous solution is also relatively high. Generally, the surfactant having a large number of branches in the hydrophobic group has a poorer intermolecular action than the linear one, so that the surface viscosity of the solution is small and the foam stability is also poor. For example, a surfactant prepared by chemically combining unsaturated olefins (the SO4 group is in the middle of a hydrocarbon chain) has a poor bubble stability of an aqueous solution, and a linear surfactant such as potassium laurate or sodium lauryl sulfate is soluble in water. The foam stability of the crucible is better.
Second, defoaming
Foaming is a requirement of the industrial production sector. In some cases, the formation of foam and excessive stability may cause a lot of trouble in production. Therefore, how to defoam is also a major research topic.
Defoamers commonly used in the industry are liquids that are easy to spread on the surface of the solution. When the liquid spreads on the surface of the solution, it will take away a layer of solution on the adjacent surface, causing the liquid film to be partially thinned, causing the liquid film to rupture and thus foam. damage. Ether, isovaleryl, etc. are all such defoamers. Therefore, the reason for the satiety is on the one hand that it is easy to spread, and the adsorbed antifoaming agent molecules replace the getter molecules to form a film with poor strength. At the same time, part of the solution of the adjacent surface layer is taken away during the spreading process, so that the foam liquid film is thinned, the stability of the foam is lowered, and the foam is easily broken.
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