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. The gel can be useful in a food processing plant, where the sensor could indicate whether food that must remain dry has been overly exposed to humidity.
Ingredients
Researchers wanted to develop something that was ‘tunable’ so 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. 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 Key
Key to manipulating the thickness of the poly-2-vinyl-pyridine (2VP) layer is to give the nitrogen’s on each segment of the 2VP block a positive charge, yielding a polyelectrolyte chain that can swell to more than 1,000 percent its volume in water. If the charges along the chain’s backbone are electrically shielded from each other, for example by adding a high concentration of salt ions to the water that has permeated the gel, the 2VP chains collapse into disordered tangles, like balls of string. When the salt ions are washed away, the 2VP positive charges again repel each other and the chain extends, causing each 2VP layer to expand and the material to reflect a different color.
Cool and interesting
This is an amazing creation - though different but a reliable sensor for sure, quite effective and informative too, changing color means that there is something wrong and you can react before hand. I can relate it to my Dad’s expression whenever I come late, if the color of his face turns Red, it gives me a clear indication that something is wrong and a much rooted excuse has to be implied this time around.
