Magazine article Science News

Wettable Latex Makes for Drier Surroundings

Magazine article Science News

Wettable Latex Makes for Drier Surroundings

Article excerpt

Diapers absorb urine, but they don't hold it very well. To keep babies' bottoms drier, one needs a material that likes being wetter.

Disposable diapers, like many consumer products, contain elastomer - a stretchable material made of chain-like molecules called polymers. Elastomers make room for urine as then baby wets. But because elastomer surface lack the energy to hold on to water, droplets bead up and spill off, and the diaper leaks.

Adding soap can lower the surface tension so that the drops stay on longer, but eventually the soap washes off. Thus, most elastomers are swellable but not "wettable," says Isao Noda, a polymer scientist with Procter & Gamble in Cinnati.

A new latex film promises to fix that, he says. In the March 14 Nature, Noda describes an elastomer that any water molecule can love. Unlike other rubber materials, its surface attracts water. So instead of rolling off, the droplets spread flat and stay put.

"Up to now, you've never had that property before [in rubber]," says Carl C. Gryte, a chemical engineer at Columbia University in New York City.

The secret lies in a hybrid molecule known as a block copolymer, which Noda mixes with latex particles when making his elastomer. This hybrid consists of two molecular chains attached at their tail ends. One, called the polar chain, sticks out of the finished elastomer film and contains lots of oxygen, which attracts water molecules. The other chain branches as the elastomer forms, entwining itself with the latex particles like an overgrown root. …

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