9. What is the difference between the wetting and penetrating effects of surfactants?
Answer: Drop a drop of water on a clean glass surface. The water droplets will spread quickly on the glass surface. The air-glass interface is replaced by the water-glass interface. This phenomenon shows that water can wet the glass. If a layer of paraffin is coated on the glass surface, the water droplets cannot spread on the paraffin surface and exist in the shape of balls on the paraffin surface, indicating that water cannot wet the paraffin surface. However, if an aqueous solution containing surfactants such as stretching powder or penetrating agent JFC is dropped on the surface of paraffin, the surface of paraffin can be quickly wetted. This effect of wetting an object with the help of surfactants is called wetting. However, this phenomenon cannot penetrate into the interior of the glass, because the glass has no capillary effect and can only produce wetting. For fabric products, if a drop of water is dropped on natural cotton cloth, the water drop will be in the shape of a ball, which is also considered non-wetting. The reason why it is difficult for water to wet natural cotton cloth is not only the presence of air in the fibers, but also the presence of grease and wax in the fibers. If the natural cotton cloth is scoured and bleached, the water droplets will quickly spread on the natural cotton cloth and penetrate into the fiber, displacing the air, and replacing the air-fiber interface with the solution-fiber interface. If a few drops of penetrant such as JFC are dropped on the same unbleached natural cotton cloth, the water droplets can also spread on the natural color cotton cloth and penetrate into the interior of the natural color cotton cloth. This effect of allowing water to penetrate into an object with the help of surfactants is called osmosis. The reason why water can wet and penetrate into the fiber is that the fiber is a porous material with a huge surface area, which allows the solution to quickly spread along the fiber and enter the fiber gaps due to capillary action, displacing the air until it is completely Moisturize. There is no essential difference between wetting and penetration. The former acts on the surface of the object, while the latter acts on the interior of the object. Both can use the same surfactant, so the wetting agent can also be called a penetrating agent.
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