Tuning Solvent-Dependent Color Changes of Three-Dimensionally Ordered Macroporous (3DOM) Materials Through Compositional and Geometric Modifications

The color of three-dimensionally ordered macroporous (3DOM) silica, alumina, and zirconia ("inverse opals") was shown to change with the refractive index of the fluid occupying the macropores. The pores of 3DOM alumina, 3DOM zirconia, and 3DOM silica with two different pore sizes were filled with air, methanol, ethanol, isopropanol, tetrahydrofuran, dimethylformamide, toluene, and 1,2-dibromoethane. The wavelength (l) of the stop band (measured by diffuse-reflectance UV-vis spectroscopy) was found to be linearly related to the refractive index (RI) of the fluid filling the pores. The slope and intercept of the l-RI line could be adjusted by changing the pore dimensions and the composition of the walls. The slope was steeper than in artificial opals composed of close-packed silica spheres. The fitted l-RI line was used to calculate the filling fraction of the ceramic and spacing between voids. Calculated pore spacings matched measurements from the scanning electron microscope (SEM).