Light-induced color changes of microgel-based etalons.

Poly(N-isopropylacrylamide) (pNIPAm) microgel-based etalons were used to fabricate systems that change visual color in response to light exposure. These systems were fabricated by adding pH responsive microgel-based etalons to a solution composed of the photoacid o-nitrobenzaldehyde (o-NBA). Upon exposure of this system to ultraviolet (UV) irradiation, the photoacid released a proton, lowering the pH of the solution. Since the pNIPAm microgel-based etalon was responsive to pH, the etalon changed its optical properties and, hence, visual color. We went on to show that patterned etalons could be fabricated, which only contained pH-responsive microgels in specific regions. These etalons only changed color in the pH-responsive regions, to yield patterns that change color upon UV light exposure. Finally, the color of the etalon was shown to be fully reversible and could be switched multiple times. These unique systems could potentially be used for display technologies, and as a controlled/triggered drug delivery system.