QUESTION: I heard on some science TV show that "they," to this day, don't know for sure what makes glue work. Is this true? What does make glue stick? Does it depend on the type of glue? What do glues share in common?

– Louise McGarvey, La Jolla

ANSWER: We take sticky notes, glue sticks, super glue and tape so for granted it may come as a surprise that developing new adhesives is a very active area of research. Understanding what makes stuff sticky is key to making stickier adhesives or adapting them to new purposes.

Although people use the words glue and adhesive interchangeably, glues, which are made from natural materials, have been around a lot longer than adhesives, which are made from synthetic materials. According to archaeologists, ancient civilizations used sticky materials like tree sap to repair broken pottery as far back as 4000 B.C.

White glues (or adhesives), such as Elmer's, work by evaporation. As the water in Elmer's evaporates, the polyvinyl acetate latex that has spread into the crevices of the material being glued forms a pliable bond.

Super glue has as its main ingredient a chemical called cyanoacrylate. The presence of water causes cyanoacrylate molecules to start linking up with each other until they form a strong plastic mesh. Super glue is all-purpose because pretty much everything has trace amounts of water on its surface.

Sticky notes are easily removable and restickable because the adhesive on the back of the notes consists of a thin, bumpy layer of microspheres. These little spheres stick to a surface, but the gaps between the spheres remain unstuck.

Even with synthetic sticky materials, scientists still have a thing or two to learn from Mother Nature. Geckos, with their amazing ability to run up walls, have been a recent source of inspiration. Geckos have about 500,000 microscopic hairs, called setae, on each foot. At the end of each of the setae are 1,000 branches tipped with pads called spatulae.

Unbalanced electrical charges around molecules in the spatulae and molecules in the surface to which the gecko is clinging interact, drawing the molecules together. These interactions, summed over the millions of spatulae in each foot, create a very strong bond.

Using this knowledge, researchers have developed a super sticky material with "nanobumps" that resemble the spatulae on geckos' toes. If it can be mass-produced, this material could be made into reusable tape that even works under water.

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Sherry Seethaler has a doctorate in science education and is a UCSD science writer and educator. Send your scientific questions to her at Quest, The San Diego Union-Tribune, P.O. Box 120191, San Diego, CA 92112-0191. Or e-mail sseethaler@ucsd.edu. Please include your name, city of residence and phone number.

copyright 2004 The San Diego Union Tribune