Combination of microspheres and sol-gel electrophoresis for the formation of large-area ordered macroporous SiO2

Abstract

A simple and effective fabrication scheme involving sequential electrophoretic depositions of polystyrene (PS) microspheres (500 nm and 1 mu m in diameter) and SiO2 sols (similar to 5 nm in diameter) to produce large-area ordered macroporous SiO2 inverse opals (2 x 2 cm(2)) on ITO substrates is demonstrated. The zeta potentials for PS microsphere suspension and SiO2 sols are measured to determine an optimized processing window in which both samples carry negative surface charges and sol-gel transformation can be properly implemented. Our approach entails the electrophoresis of PS microspheres to render a colloidal crystal with negligible defects. Afterward, SiO2 sols are infiltrated to the interstitial voids among the closely-packed PS microspheres via another electrophoresis process, followed by an oxidation treatment to remove the PS colloidal template and complete the densification of SiO2 gels. The resulting SiO2 inverse opals reveal impressive surface uniformity and structural integrity. Fourier transform infrared spectroscopy confirms the complete removal of PS microspheres, leaving an intact SiO2 skeleton, whereas X-ray diffraction pattern indicates its amorphous nature.