In Situ Monitoring Dielectric Spectroscopy And Particle Growth Mechanism Investigation On The Synthesis Of Silica Nanoparticles With Microemulsion Method

The microemulsion method is one of the most important methods for the synthesis of nanoparticles with uniform size and morphology.The synthesis of nano-particles in microemulsion is a dynamic process,which includes chemical reaction of precursor,nucleation and growth.The objective of this work is to use dielectric spectroscopy to monitor the synthesis of nanoparticles via microemulsion method in-situ and in real time,based on which to further investigate the mechanism of particle growth in the synthesis process.To this end,the static dielectric behavior of Triton X-100/n-hexanol/cyclohexane/ammonia solution system was studied means of dielectric spectroscopy,through varying the water content and concentration of electrolyte solution.Three relaxation processes were observed in the frequency range of 10³-10⁹Hz,which are confirmed to be mainly ascribed to counterion polarization and interfacial polarization,with the interfacial polarization dominating The synthesis process of Si O₂ nanoparticles via microemulsion method was then monitored in situ and in real time through dielectric spectroscopy,and the dielectric parameters of the relaxation were obtained in line with Cole-Cole formula,based on which,the variation of phase parameters,such as the dielectric constant of dispersed particle and its volume fraction,with synthesis time was determined in accordance with Hanai theory and corresponding dielectric analytical method through analyzing the variation of these dielectric and phase parameters with synthesis time,information on the dynamics of hydrolysis of precursors,nucleation of silica species,and particle growth was studied.Finally,the influence of temperature,ammonia content and tetraethyl orthosilicate content on the size,morphology and structure of Si O₂ nanoparticles synthesized by microemulsion was investigated by using dielectric spectroscopy coupled with other characterization methods.The results suggest that,the dielectric behavior of the synthesis system can well describe the dynamics of the synthesis process under different conditions.With increase in temperature,the reaction rate is larger and the relaxation strength decreases faster.As the ammonia content increases,the reaction rate increases due to increase in the concentration of reactant and catalysis,and the relaxation strength decreases faster.With the increase of the content of tetraethyl orthosilicate,the relaxation strength increases also faster,and the dynamics of the synthesis process becomes faster.In summary,the results showed that dielectric spectroscopy technique is a characterization method able to monitor the kinetic process of the synthesis of nanoparticles with microemulsion method in situ and in real time and to provide important kinetic information.