Small-scale glues stick to surfaces

A blob of glue might work for assembling a model airplane, but connecting microscopic particles for nanotechnology applications requires more precise adhesives. A new study shows that by choosing materials known to bind to a particular surface at the molecular level, researchers can create the nanoscale glues they need.

Roger J. Davey and his colleagues at the University of Manchester Institute of Science and Technology in England, used crystals of saccharin to test the ability of three compounds to act as molecular glues. Saccharin crystals can assume a structure known as a twin: The planes of atoms come together to form an interface with one side presenting the mirror image of the other.

“Since we had a structural model of the twin interface,” says Davey, “we decided to see if we could design a molecule that would bridge the interface and act as a glue.”

The researchers chose ethylene glycol, indigo, and hydroquinone as adhesives that could bind to exposed oxygen atoms on both sides of an interface. When Davey and his colleagues added ethylene glycol or indigo to a solution of saccharin and allowed the mixture to crystallize, the saccharin formed twins much more frequently than a pure saccharin solution did, indicating that the added molecules helped twin surfaces adhere to each other.

“Knowing the interfacial structure, we could select glue molecules that fit across the interface like pieces in a jigsaw,” Davey says. Ethylene glycol and indigo molecules are both 0.47 nanometers across—just the right size to bridge the gap and stabilize the twinned crystals.

Hydroquinone, however, is too large to fit in the space, so it destabilized the crystals. Indeed, the researchers saw that almost no twins formed in that saccharin solution. Davey and his colleagues report their findings in the Dec. 16, 1999 Nature.

In addition to gluing together tiny particles, molecular adhesives could attach small amounts of active chemicals to a crystal matrix that would later dissolve, Davey suggests, thus creating controlled-release drugs.

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