Effects of medium composition on optical properties and microstructures of non-close-packed colloidal crystalline arrays

The effects of medium composition on the optical properties and microstructures of non-close-packed silica colloidal crystalline arrays have been demonstrated. Water–alcohol mixtures were used as dispersion media for these arrays. Optical properties and microstructures were examined using angle-resolved reflection spectra measurements. The Bragg diffraction peaks of the colloidal crystalline arrays shifted with changing of concentration or hydrocarbon number of alcohol. With an increase in concentration or hydrocarbon number of alcohol, the effective refractive index of the dispersion increased and the interplanar spacing of the colloidal crystalline array decreased. The increase in effective refractive index was caused by an increase in the refractive index of the mixed medium with the change in solvent. The decrease in interplanar spacing of the array was caused by decreased electrostatic repulsions between the silica spheres with decreasing dielectric constant. The current work suggests new possibilities for the control of optical properties and microstructures of colloidal crystalline arrays.