Researchers at the Massachusetts Institute of Technology (MIT) have created a new structured gel that can rapidly change color in response to a variety of stimuli, including temperature, pressure, salt concentration, and humidity. The gel could be used as a fast and inexpensive chemical sensor. These environmental sensors could be used in food processing plants, where it would indicate if food that must remain dry

has been exposed to

high levels of humidity.

Photonic gel crystals demonstrate the “tenability” of materials made fromalternating layers of hard and soft polymers. The soft polymers are easilyswollen with liquid or vapor causing the materials to reflect different colorsof light based on the way their molecules are chemically tuned. (Photoby Donna Coveney)
Structured gels have an internal pattern such as layers. A critical component of the structured gel developed at MIT is a material that expands or contracts when exposed to certain stimuli. Those changes in the thickness of the gel cause it to change color, through the entire range of the visible spectrum of light. Objects that reflect different colors depending on which way you look at them already exist, but once those objects are manufactured, their properties can’t change. The MIT team set out to create a material that would change color in response to external stimuli.

To do that, they started with a self-assembling block copolymer thin film made of alternating layers of two materials, polystyrene and poly-2-vinyl-pyridine. The thickness of those layers and their refractive indices determine what color light will be reflected by the resulting gel.

By keeping the thickness of the polystyrene layer constant and altering the thickness of the poly-2-vinyl-pyridine layer with external stimuli such as pH and salt concentration, the researchers were able to change the gel’s color in fractions of a second.

The MIT team is also working on a gel that changes color in response to applied voltages.

For more information, click here.

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.