What material is the raincoat? Why is it rainproof?

Why can rainproof cloth protect against rain?

On rainy days, people who go out either wear umbrellas or raincoats. Why is the raincoat impervious? The secret lies in making materials. Take the cloth raincoat for example, it is made of rain-proof cloth (ordinary cotton cloth treated with waterproof agent). Waterproofing agent is a kind of paraffin emulsion slurry containing aluminum salt. Paraffin wax becomes fine particles after emulsification, which are evenly distributed on the fibers of cotton cloth. Paraffin and water don't get along. When water meets paraffin, it will form oval drops and roll on them. It can be seen that paraffin wax plays a role in rain protection. In physics, this watertight phenomenon is called "impermeable phenomenon". Once water meets ordinary cotton cloth, it permeates through capillaries between fibers, which is the so-called "infiltration phenomenon".

Objects are made up of molecules. The interaction between molecules of the same substance is called cohesion; The interaction between molecules of different substances is called adhesion. When cohesion is less than adhesion, "infiltration phenomenon" will appear; On the contrary, there will be "no infiltration phenomenon". Raincoats are watertight precisely because the cohesion of water is greater than the adhesion of water to raincoats.

Physics also tells us that the cohesion of water forms surface tension on the surface of water. The surface tension of water makes the water surface form an elastic film. When water comes into contact with other objects, as long as the water does not penetrate into it, this elastic membrane is complete and can tightly wrap the water. Someone has tried: cleverly pour water into a metal mesh soaked in wax, so that water does not leak out of the mesh.

Ordinary glass looks smooth and bright. However, when the water meets it, it is tightly entangled, which brings all kinds of troubles: when it rains, the rain on the windshield of the car blocks the driver's line of sight, which is very unsafe, so we have to start the paddle to drain water; When people who wear glasses drink hot water, their lenses are immediately covered with fog and steam, blocking their vision and seeing nothing.

Knowing the characteristics of water surface tension and the relationship between water cohesion and adhesion, people not only skillfully made raincoats, but also made a novel "annoying" water glass-coating a silicone chemical film on ordinary glass, which greatly weakened the adhesion of fog to glass. The use of this waterproof glass as a lens relieves the fogging distress for people wearing glasses; If this kind of glass is installed on the front window of the car, there is no need to pick it. Now you should be able to tell the truth that tarpaulin umbrellas don't leak!