Shulou(Shulou.com)11/24 Report--

Original title: "how on earth can glass not get foggy? Hey!" | serious play "

Everyone must have observed the phenomenon of glass fogging.

Like on a car window when it's cold or on a mirror in the shower.

The difference in temperature and the presence of water vapor may cause fog on the glass surface.

If you want to prevent fog, you must first know where the fog comes from.

Let's explore the horn!

Laboratory equipment standard cup, electric kettle, glass container, soapy water, oil, moisturizing milk

In the course of the experiment, first of all, we use an electric kettle to boil the right amount of water to about 90 degrees.

Generate enough water vapor to speed up the experiment

Pay attention to safety and avoid burns during the whole process.

Buckle up the glass bowl

In an instant, there was a layer of mist on the glass bowl

This is true even in places where there is water left.

You may have heard of such a method when facing the fog of swimming goggles: apply soapy water.

Let's try it.

For comparison, here paper is used to wipe off the soapy water on one side of the bowl.

The effect is very good.

The soaped part is still clear and transparent.

What if we continue to steam this glass bowl?

As more water vapor pours in

The parts that were originally protected also began to be eroded by fog.

In the last century, astronaut helmets removed fog by using electric heating wire and blowing dry oxygen.

It will also be combined with a simple anti-fog agent to remove fog.

Antifogging agent is a mixture of surfactant and oil.

Although we can't produce a stable antifogging agent.

But we can try adding oil to the glass bowl soaked in soapy water.

Driven by hot air and gravity

The excess oil will gather together and flow out.

Reveal a clean transparent surface

Because the flowing oil body will flow away with part of the soap.

Local fog occurs more often than pure soapy water.

But the rest of the place seems more lasting.

The local fog is also finer than before.

It's kind of like ground glass.

As another group of controls

We can also try to apply oil only.

The result is almost no antifogging effect.

But the resulting droplets will be more uniform than the dried parts.

In the experiment, we should also pay attention to avoid letting the water boil completely.

Boiling water vapor cools into larger droplets as it rises

Cause the protective film to disintegrate quickly.

A lipophilic and hydrophilic coating similar to an antifogging agent.

The editor looked at the house and his head was crooked.

Does moisturizer have the power to fight a war?

Try to spread it evenly and give it a try:

It still seems to have a certain effect.

But it's a little nearsighted.

Zoom in.

The moisturizing milk converges the fog into larger droplets

So you can not see the other side of the glass very clearly.

The principle explains that the fog on the glass is composed of small water droplets that are not liquefied as expected. the radius of these small water droplets is very small, and the surface with large curvature makes the adjacent parallel light go their separate ways after refraction, making it difficult to image the objects behind the glass. so it's foggy as a whole. Shall we just make the droplets larger and the curvature smaller? After all, if the water is a complete film, it should not have much impact on the imaging.

The finished antifogging agent does use this principle to remove fog, reducing the surface tension through the action of surfactants or hydrophilic particles, so that the liquefied water vapor forms a water film instead of water droplets. However, when doing experiments at home, because the soapy water itself is not uniform enough, the soap components in places with low concentrations will gather together due to the affinity between the hydrophobic ends after natural evaporation, leaving parts that have lost their ability to remove fog. is gradually "eroded". Adding the right amount of oil also makes the structure of some local water-soap-oil more lasting.

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: litchi & Hetang & Tingzi

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