Everyone knows it: If you get into your car early in the winter morning and the windshield is frozen, your first choice is usually an ice scraper. Window defrosters promise much less effort and no cold hands. But how do these actually work?
De-icing sprays consist of a mixture of alcohols, such as isopropanol and glycerin. Isopropanol lowers the freezing point of water on the plate and causes the ice to melt. Glycerin is a viscous liquid and evaporates much less quickly than other alcohols. Glycerin is added so that the de-icer stays on the car window longer and prevents ice from forming again.
The principle that certain substances can lower the freezing point of water is also used in nature. Examples of this are fish that live in the Arctic. They produce antifreeze proteins and glycerol to hibernate safely in cold water.
Although it may seem tempting, hot water is not a recommended method for defrosting. A rapid temperature difference can cause cracks in the windshield as the glass on the side that has been soaked with water expands faster than the other side that is still cold.
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