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Name: Nathan
Status: Other
Grade: Other
Location: CO
Country: USA
Date: July 2006

When fluorine is used to repel water on fabrics such as DWR-Durable Water Repellency (a topical surface treatment used on garments), is it increasing or decreasing the surface tension on the fabric?

Fluorine (the element) is not used to make fabrics water repellant. Fluorine is a toxic, corrosive gas. What is used are compounds formed between carbon fluorine and occasionally other elements, generically referred to as "fluorocarbons". The fluorine atoms in these compounds hold on to their electrons very tightly, so they are not able to be attracted to other molecules such as water. As a result the surface tension of the fabric coated with the fluorocarbon is decreased. This causes the water molecules, which already like to associate with one another, do so even more when in contact with the fluorocarbon. The result is that the water "beads up" and flows off the fabric rather than being attracted to the fibers.

Vince Calder

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