MIT researchers 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.
A critical component of the structured gel 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.
"We wanted to develop something that was 'tunable,'" said Thomas, who is head of MIT's Department of Materials Science and Engineering.
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.
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