The ice

Researchers at the Massachusetts Institute of Technology (MIT) have created a gel capable of changing color rapidly in response to a wide variety of stimuli, such as temperature , pressure , salt concentration or humidity . Among other applications, the new material could be used as a fast and cheap chemical sensor , for example in a food processing plant, where a color change would indicate whether ingredients that should be kept in a dry environment have been exposed to excessive humidity.

Until now there were objects capable of reflecting different colors, but once manufactured their properties did not change. Scientists at MIT’s Department of Materials Sciences and Engineering have overcome this limitation by combining several layers of two materials, polystyrene and poly-2-vinyl-pyridine. The thickness of these layers determines which light waves the gel reflects at each moment, and therefore its color. External stimuli such as pH or salt concentration can change that thickness (and color) in a matter of seconds, according to its creators in the latest issue of the journal Nature Materials .