Serendipity: Hitting on the right note

SOME PEOPLE view serendipity as a form of divine intervention, a notion that is supported by the story of Art Fry, who worked for 3M in St Paul, Minnesota. Fry sang in the choir of his local Presbyterian church, where he was in the habit of slipping scraps of paper into his choir book so that he could find the next hymn more quickly. One Sunday in 1974, a paper marker fell from his book, and he found himself in the embarrassing position of not being ready to sing.

During the sermon that followed, he sat in his pew wondering if there was a way to make a more efficient bookmark. "I don't know if it was a dull sermon or divine inspiration," recalls Fry, "but my mind began to wander and suddenly I thought of an adhesive that had been discovered several years earlier by another 3M scientist, Dr Spencer Silver."

Silver had been trying to develop a new type of strong glue, but all his attempts ended in failure, since he only managed to create something that was slightly sticky.

Luckily, slightly sticky was exactly what Fry needed to create his sticky bookmark, now known as the Post-it Note. Silver's concoction was strong enough to support the weight of a piece of paper, yet weak enough not to tear the paper fibres when the note was removed.

Fry worked on the idea for the next three years, exploiting 3M's "15 per cent policy", which allows researchers to spend 15 per cent of their time doing whatever they like. Today there are over 400 Post-it Note products, including virtual Post-its for computer screens.

The science of stickiness is one of the most challenging areas of modern research, and it was only this year that researchers uncovered a new explanation for the sticking power of materials such as Post-it glue. The standard theory for predicting the force required to remove an object from a sticky surface assumes that all the stickiness is caused by the attraction between the glue molecules and the molecules of the object. This theory turns out to be inadequate, because it implies that the stickiness should be 10,000 times weaker than it actually is.

Recently, French physicists Cyprien Gay and Ludwik Leibler calculated the effect of an added factor, namely the millions of tiny bubbles at the interface between the sticky glue and whatever it is stuck to. Each bubble is roughly one thousandth of a millimetre in diameter, and each one acts as a miniature suction cup. When we attempt to pull an object away from a sticky surface, the bubbles are reluctant to expand, and they resist the pull. Gay and Leibler's idea seems to make sense, but it still has to be tested, so right now experimenters are filling their labs with sticky stuff in an attempt to measure the effect of the bubbles.

Simon Singh is the author of `Fermat's Last Theorem' (Fourth Estate, pounds 6.99)