( Changing a surface from sticky to slipp...)Sticky surfaces turn slippery with the flip of a molecular light switch

Changing a surface from sticky to slippery could now be as easy as flipping a molecular light switch. Researchers at Rensselaer Polytechnic Institute have created an "optically switchable" material that alters its surface characteristics when exposed to ultraviolet (UV) light. The new material, which is described in the June 19 issue of the journal Angewandte Chemie International Edition, could have a wide variety of applications, from a protein filter for biological mixtures to a tiny valve on a "lab-on-a-chip."

Synthetic polymer membranes are used in a variety of applications based on the science of "bioseparation" -- filtering specific proteins from complex liquid mixtures of biological molecules. But proteins often stick to these membranes, clogging up their pores and severely limiting their performance, according to Georges Belfort, the Russell Sage Professor of Chemical Engineering at Rensselaer and corresponding author of the paper.

"We asked ourselves, can one use light to help the proteins hop on and hop off? We have shown that when one changes light, the proteins don't stick as well," Belfort says.

Operators need an inexpensive way to clean these membranes while they are still in place, rather than periodically removing them from the application environment, Belfort says. But currently the only cleaning options involve expensive chemicals or labor-intensive procedures that result in significant process down-time.

To make the new materials, Belfort and his coworkers attached spiropyran molecules to a widely used industrial polymer, poly(ether sulfone). Spiropyrans are a group of light-switchable organic molecules that exist in a colorless, "closed" form under visible light, but switch to a reddish-purple, "open" form when exposed to UV light. This change leads to an alteration of the new material's polarity, or the chemical structure of its atoms.

In switching from non-polar to polar, the material becomes less attracti
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Source:Rensselaer Polytechnic Institute

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