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Analytical Chemistry

Sticky Notes

Serendipitous chemical discovery and a bright idea led to a new product that is ubiquitous

by Bethany Halford
April 5, 2004 | A version of this story appeared in Volume 82, Issue 14

Do taxes. call mom. buy milk. In the modern world of multitasking, sticky notes are like memos from my memory. And I'm not alone. By some estimates, more than 1 trillion individual sticky notes have been sold worldwide since the product was first introduced.

The adhesive that allows the omnipresent little notes to be stuck, unstuck, and restuck was discovered nearly 35 years ago. It may seem surprising, then, that the sticky notes weren't readily available throughout the U.S. until 1980.

Back in 1968, Spencer F. Silver, a chemist working on pressure-sensitive adhesives for 3M, found that when an acrylate copolymer was made in a particular way, it formed a suspension of cross-linked microspheres. The microspheres didn't dissolve in solution, but instead swelled to twice their original diameter. Silver says that the "pasty mass" of microspheres could simply be sprayed or coated on a surface without clumping. Once sprayed on, the solvent quickly evaporated and the microspheres returned to their original size.

"The key to the adhesive is that it forms a sparse monolayer," Silver explains. Viewed with a scanning electron microscope, the adhesive has a pebbled surface, a bit like the surface of a basketball. By comparison, the adhesive on a piece of permanent tape looks flat and featureless under the same degree of scrutiny.

Although he didn't have any particular product in mind when he made the adhesive, Silver knew that he had something special. It was truly serendipity, he says. Still, turning the fortuitous discovery into a profitable product took perseverance. 3M spent years trying to develop an application for the adhesive, and at one point came up with a sticky bulletin board coated with the glue. However, dust and dirt eventually built up on the board, diminishing its sticking power as well as its popularity. Then, Silver says, in 1974 "Art Fry turned the concept around and transformed the world into a bulletin board."

Legend has it that Fry, a chemical engineer for 3M, was singing in his church choir when he hit upon the idea for a removable sticky bookmark. He remembered Silver's glue, and the sticky note, or Post-it note, as it would come to be known at 3M, was born.

Fry's story has become inventor's folklore, but Silver says it's important to remember that in the years between its discovery and Fry's idea, the adhesive "didn't just sit on some executive's desk." Many people at 3M were working hard to make sure the unique adhesive wasn't abandoned.

Luckily, Silver's adhesive turned out to be perfect for Fry's idea. According to Greg Anderson, technical director of 3M's office supplies division, the adhesive's bumpy surface of microspheres allows for a limited number of touchpoints and makes paper coated with the adhesive removable and restickable. Silver adds that the adhesive layer is just the right thickness--about the same thickness as the paper, in fact--to give it the desired stickiness. He also points out that even though the adhesive is as thick as the note it's stuck to, the microspheres' size and softness are such that they fit within the structure of the paper when compressed. That's why, in an unopened package of Post-its, it's hard to figure out which one is the sticky edge.

There's also plenty of other chemistry that goes into making the notes. For example, the notes require a coating on one side so that the adhesive stays stuck to the paper. As 3M explains at length on the Post-it website, the company wanted to ensure that the coatings and adhesive wouldn't render the note unrecyclable.

Since their introduction, sticky notes have managed to gain quite a following, even in some unexpected circles. "Post-it notes are smart, beautiful, and cheap. That's the apotheosis of great design," gushed Paola Antonelli, curator of architecture and design at New York's Museum of Modern Art, to Newsweek last year. Post-its have garnered a spot in MoMA's collection, and from April 8 to Sept. 27, they'll be featured, along with 120 other everyday items, at the museum's "Humble Masterpieces" exhibit.

While you may find sticky notes in MoMA's exhibition halls, don't try using them on books in MoMA's library. They're banned there and at several other libraries. That's because archivists have found that the adhesive leaves behind a slight residue that over time accumulates dirt and could damage books and other historical documents.

In 1988, Susan Lee-Bechtold, a chemist with the National Archives & Records Administration's document conservation branch, was asked to investigate the effects of sticky notes on paper-based records following some reports that the notes might be harmful. "We found people were putting them on original records, and that concerned us," Lee-Bechtold says.

Her experiments showed that charcoal dust stuck to areas of paper that had once adhered to sticky notes. It didn't matter if the notes had been left on the paper for a couple of weeks or just a second. Lee-Bechtold also concluded that while the acrylate copolymer wouldn't discolor paper over time, it did have the potential to leave "long-term stickiness," which could eventually damage records by sticking to file folders, other records, or polyester sleeves meant to protect delicate documents.

Lee-Bechtold recommends not using the notes on permanent records. And it's probably not a great idea to use sticky notes to mark important passages in rare books and journals. Nevertheless, for the millions of us who are continually snowed under by paper in our offices and homes, sticky notes have proven to be an indispensable asset. They're also reminders of the success that comes from sticking to a good idea.



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