on the surface of the hydrophobic material, round water droplets tumble and jump, which always looks very comfortable. In addition to looking good, hydrophobic materials are also very practical. For example, it can be made into an umbrella that stays dry at all times.

how do hydrophobic materials come from?

if you want to drive water off an object, you first need a material that is inherently incompatible with water. For example, the surface of lotus leaves is covered with non-hydrophilic wax, while many waterproof fabrics use materials such as polytetrafluoroethylene (yes, Teflon).

if we want to further improve the hydrophobicity, we should focus on the microstructure of the object surface. If you look at the lotus leaf under a microscope, you can see that there are actually many small protuberances on the surface, these structures further reduce the contact between water droplets and the surface, and many man-made hydrophobic surfaces adopt the same idea.

how hydrophobic is it?

to measure how hydrophobic an object's surface is, we usually look at the "contact angle" between it and the water droplet, that is, the angle between the edge tangent of the water droplet and the solid surface.

(the angle marked in the figure is the contact angle. Joris Gillis~commonswiki)

the more the droplet shrinks like a round sphere, the larger the angle, which means that the surface is more hydrophobic. When the contact angle is greater than 90 °, it can be called hydrophobic. If it can reach more than 150 °, it is very hydrophobic.

(the super-hydrophobic material can make the contact angle of the water drop reach more than 150 °, even close to 180 °, and the water drop looks like a glass bead. Photo Source: web.mit.edu)

so how is the performance of the hydrophobic umbrella? The following picture shows small water droplets (pigment staining) on the surface of a hydrophobic umbrella. Although the water droplets have not completely shrunk into a sphere, it can be seen that the contact angle is an obtuse angle, and it is easy to roll off when the umbrella is tilted, which is enough for daily waterproofing.

Why are umbrellas hydrophobic?

ordinary umbrellas are naturally made of fabric that is not very absorbent, but many umbrellas are not that waterproof and the cloth will still be soaked with water. The umbrella is always wet after use, not only should it be bagged to prevent dripping, but also should be held up to dry. On rainy days, offices, classrooms and hallways are always full of umbrellas. If you don't have a place to say, you have to lose a few of them.

(fruit shell offices also covered with umbrellas …... )

and if you improve the hydrophobicity of the umbrella cover, Rain Water will no longer infiltrate the fabric of the umbrella surface, and it will easily roll down by himself, which will be much easier to use. As long as you throw it away, you can put it away.

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