Large-Scale Colloidal Self-Assembly by Doctor Blade Coating

Here we report a simple and roll-to-roll compatible coating technology for producing three-dimensionally highly ordered colloidal crystal-polymer nanocomposites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear-align silica microsphere-monomer suspensions to form large-area nanocomposites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension and the coating speed. The correlations can be explained by adapting the models developed for conventional doctor blade coating. We further demonstrate that the doctor blade coating speed can be significantly increased by using a dual-blade setup. The optical properties of the self-assembled structures are evaluated by normal-incidence reflection measurements and the experimental results agree well with the theoretical predictions using Bragg’s law and scalar-wave approximation model. The templated macroporous polymer membranes have also been demonstrated in a variety of important technological applications ranging from size exclusive bioseparation and smart windows to self-cleaning diffractive optical filters and vapor detectors.