Large-area 2D microgel colloidal crystals fabricated via benzophenone-based photochemical reaction

We report a simple method to fabricate high quality, large area 2D colloidal crystals (CCs) of a soft colloid, poly(N-isopropylacrylamide) (PNIPAM) microgel. The microgel spheres were first assembled into a 3D CC. The first 111 plane of the 3D CC close to the substrate was then fixed in situ onto the substrate via a photochemical reaction of the benzophenone moieties immobilized on the substrate surface. The resulting 2D microgel arrays exhibit a high degree of ordering. The interparticle distance in the 2D array can be tuned by the concentration of the microgel dispersion. Increasing the concentration of the microgel dispersion will reduce the interparticle distance of the resulting 2D array. Because large area 3D microgel CCs can be facilely fabricated, this method allows for the fabrication of large area 2D microgel CCs. In addition, the method allows the 2D CCs to be fabricated on nonplanar substrates.