Spencer F. Silver, the chemist who invented the adhesive that makes 3M’s Post-it notes stick, died May 8 at the age of 80. Silver worked at 3M for 30 years, from 1966 to 1996. He was awarded 37 patents for his work with the company, along with numerous honors, including the 1998 American Chemical Society Award for Creative Invention. He was inducted into the National Inventors Hall of Fame in 2010.
Silver was born in San Antonio, Texas, in 1941. He earned his bachelor’s degree in chemistry from Arizona State University in 1962 and his PhD from the University of Colorado, Boulder in 1966. After graduating, he joined 3M where, in 1968, Silver made his most famous discovery—the pressure-sensitive adhesive on the Post-it note (US Patent No. 3,691,140).
Silver found that when he made an acrylate copolymer in a particular way, it formed a suspension of microscopic spheres that were cross-linked to one another. Surprisingly, the microspheres didn’t dissolve in solution but instead swelled to twice their original size. The microspheres didn’t clump when sprayed or coated on a surface. Once applied to a surface, the solvent evaporated and the spheres returned to their original size.
“The key to the adhesive is that it forms a sparse monolayer,” Silver told C&EN in 2004. This sparse monolayer, which looks like the surface of a basketball when viewed with a scanning electron microscope, has some points that are sticky and some that are not. This lets paper coated with the adhesive stick, be unstuck, and then restuck. Adhesive on a piece of permanent tape, by comparison, is flat and featureless.
It took many years for the adhesive to find an application that stuck. According to inventor folklore, in 1974, Silver’s 3M colleague Art Fry realized he could use a bookmark with the adhesive to mark his place in his hymnal during church-choir practice. 3M introduced Post-it notes to the US market in 1980. Post-it notes have since become ubiquitous and one of 3M’s most successful products. Even in an increasingly paperless age, 3M sells sticky notes in dozens of sizes and colors.
“The world has lost an amazing person and a world-class scientist,” Timothy E. Long says in an email. Long studies pressure-sensitive adhesives at Virginia Polytechnic Institute and State University and worked with Silver during a summer internship at 3M when he was a graduate student in the 1980s. “I have continued research in the field of pressure sensitive adhesives due to Spence’s infectious enthusiasm for science and adhesion. He encouraged me to think about adhesion at the molecular level. Spence was truly a gentleman and a scholar extraordinaire. Our world is better because of Spence Silver.”
Silver is survived by his wife of 56 years, Linda, daughter Jennifer, and two grandchildren, Zachary and Zoë. His daughter Allison predeceased him.
This story was corrected on May 25, 2021, to clarify that Silver discovered the pressure-sensitive adhesive on the Post-it note in 1968. Because of an editing error, the article originally said that he joined 3M in that year.