| Abstract |
Microgels are excellent building blocks for photonic band gap materials (PBG) in water. Aqueous dispersions of temperature and pH responsive microgels composed by isopropylacrylamide (NIPA, 92 mol\%) and methacrylic acid (MA, 8 mol\%) show structural color in the concentration range of 44-88 mg/mL. At temperatures below the LCST of pNIPAM in water (similar to 32 degrees C), the dispersions self-organize as an elastic solid, with concentration-dependent refractive index. At 22 degrees C the color changes from red to blue when increasing the concentration. This is due to an increase in the elastic modulus. A transition to a liquid phase (characterized by a loss of the elastic modulus and of the structural color) occurs at a temperature just below the LCST. The color is a result of the diffraction of the visible light that do not propagate within the PBG as shown by the confocal reflectivity images of the microgel dispersions. |
