Large-Area Block Copolymer Photonic Gel Films with Solvent-Evaporation-Induced Red- and Blue-Shift Reflective Bands

By choice of large overall molecular weights from 0.5 to 1 M kg/mol, the lamellar microstructures of the high-molecular-weight polystyrene-block-polyisoprene (PS-PI) block copolymers (BCPs) exhibited various long periods and associated different reflected wavelengths. Interestingly, unique solvatochrom-ism-dependent red- and blue-shift reflective bands could be acquired in the PS-PI BCP gel films using a nonselective neutral solvent as an external stimulus. At low polymer concentration, red-shift of the reflectivity was attributed to the increase of BCP long period by the enhancement of the BCP segregation strength, namely, a thermodynamically controlled swelling process. In contrast, at high polymer concentration (phi(p) > 0.8), the blue-shifting reflectivity resulted from the decrease of the BCP long period by the collapse of polymer chains, namely, a kinetically controlled deswelling process. Also, well-aligned lamellar microstructures were fabricated using a shear-induced microstructural orientation. This provides a simple way to fabricate large-area 1D photonic gel films with uniform reflective colors.