Wednesday, November 2, 2011

Clarifying the fog machine

This past Halloween weekend people across America enjoyed fog machines as special effects in the movies or on TV, to spook the neighbors, or to enhance a haunted house. What is this weird artificial cloud? Where does it come from? How does it work?

Chemistry has all the answers.

Fogs are created by the dispersion of small liquid particles. For artificial fogs, the most common type of fog fluid is made of water and glycols. A glycol is a chemical compound containing oxygen and hydrogen groups that are attracted to water molecules like magnets. The result is intermolecular hydrogen bonding which connects the water molecules to glycol molecules. When these two liquids are heated inside the fog machine, the water particles convert to gas at their boiling point (100°C) and the glycol substances remain liquid, as their boiling point is upwards of 180°C. Because of the intermolecular hydrogen bonding that latches the particles together, the gas released from the fog machine is visible because the gaseous water molecules have liquid glycol molecules attached to them.

While the fog may be spooky, their is no reason to panic. There is nothing magical about its creation. Just the clever application of chemistry in the special effects world.

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