Why do plastic cups coming out of the dishwasher usually have water left on them but the glass cups are dry?
In: Chemistry
Water likes glass a lot more than it likes plastic. So it spreads out on the glass in a thin film, unlike how it beads up on plastic. (Plastic is essentially oil that is so heavy that it’s always solid, and you know oil and water don’t mix.) Beads of water that are too small cannot fall off of the plastic, while the sheet of water on glass slips right down to the bottom where it can fall off. The tiny amount of water left as a film on the glass dries very quickly: there’s almost no water in it, and it has a huge surface area.
So-called “drying agents” like Jet-Dry are special types of soap that help make all dishes act “wet” like clean glass does. No matter what material your dishes are, a drying agent helps the water stick in a thin film to them. That way, water can sheet off the way it does on very clean glass.
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