Modification of spherical SiO2 particles via electrolyte for high zeta potential and self-assembly of SiO2 photonic crystal

Abstract

Partículas esféricas de SiO 2 foram preparadas através de um novo processo de co-precipitação melhorado pelo eletrólito NaCl para carregamento e posterior auto-agrupamento em cristais fotônicos pelo método de deposição vertical. Os compostos obtidos e suas estruturas foram caracterizados por microscopia eletrônica de varredura (SEM) com espectroscopia dispersiva de energia de raios-x (EDS), potencial zeta, e espectrofotometria UV-Vis. As imagens SEM indicaram que as partículas SiO 2 eram esféricas e o diâmetro médio das partículas modificadas foi aproximadamente 380 nm, maior do que as partículas não modificadas (315 nm). Além disso, usando-se quantidade excessiva de NaCl (10 mg), uma distribuição bimodal do diâmetro das partículas de SiO 2 foi obtida e os diâmetros foram aproximadamente 110 nm e 420 nm, respectivamente. Comparando com as partículas não modificadas de SiO 2 , o espectro EDS das partículas modificadas mostrou um pico característico de Na, o qual provou a existência do elemento sódio na partícula SiO 2 . Os resultados de potencial Zeta revelaram que o potencial Zeta médio das partículas modificadas SiO 2 em etanol foi -56,6 mV, o qual é muito maior do que para as partículas não modificadas (-48,7 mV). Portanto, os cristais fotônicos que se auto-agrupam pelas partículas modificadas de SiO 2 possuem estrutura cúbica centrada na face com menos defeitos. Além disso, a espectrofotometria de UV-Vis mostrou que o gap da banda fotônica do cristal modificado de SiO 2 apresentava um deslocamento para o vermelho e o pico de absorção tornou-se mais estreito e alto.Spherical SiO 2 particles were prepared by a novel co-precipitation process improved by electrolyte NaCl for charging and further self-assembled into photonic crystal by vertical deposition method. The obtained composites and their structures were characterized by scanning electron microscope (SEM) with X-Ray energy dispersive spectroscopy (EDS), Zetasizer, and UV-Vis spectrophotometer. SEM images indicated that the SiO 2 particles were spherical and the average diameter of modified SiO 2 particles was about 380 nm, larger than that of the unmodified ones (315 nm). Moreover, when the amount of NaCl was excessive (10 mg), bimodal diameter distribution SiO 2 particles were obtained and the diameters were about 110 nm and 420 nm respectively. Compared with the unmodified SiO 2 particles, EDS spectra of the modified ones showed an obvious characteristic-peak of Na element which proved that the Na element existed in the SiO 2 particle. The results of Zetasizer revealed that the average Zeta potential of the modified SiO 2 particles in ethanol was -56.6 mV, which was much higher than that of the unmodified ones (-48.7 mV). So the photonic crystal that self-assembled by the modified SiO 2 particles possessed face-centred cubic structure with fewer defects. In addition, UV-Vis spectrophotometer showed that photonic band gap of the modified SiO 2 photonic crystal had a red-shift and the absorption peak became narrower and higher.Keywords: photonic crystal, S...

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