SIGNS OF STRESS

Abstract

PEOPLE UNDER STRESS may exhibit certain telltale signs that indicate they’re near a breaking point. Some, for example, will turn bright red just before they blow their top. Now, a new polymer does the same thing, changing color when stressed to the point of mechanical failure ( Nature 2009, 459, 68). Such a material could be used as a damage sensor that enables researchers to assess the effects of stress on polymeric materials before they fail. The new polymers can change color thanks to the addition of spiropyran molecules that undergo electrocyclic ring-opening in response to mechanical force. The resulting ring-opened merocyanine molecules are brightly colored, producing red or purple hues in the polymer, depending upon how the indicator molecule is covalently linked to the polymeric structure. The spiropyran undergoes “a force-induced reaction inside of a solid structural polymer,” explains University of Illinois, Urbana- Champaign, materials science professor Nancy R. Sottos, who spearheaded the rese...