In SituDielectric Spectroscopy Monitoring of Silica NanoparticleSynthesis in Cationic Water-in-Oil Microemulsions

In situmonitoring of microemulsion-based nanoparticlesynthesis is significant for understanding the particle formationmechanism and for advancing controlled nanoparticle synthesis bythis means. In this study, the processes of silica nanoparticle synthesis ina CTAB/n-hexanol/cyclohexane/ammonia microemulsion were moni-tored via dielectric spectroscopyin situand in real time, with theinfluences of the water content and precursor concentration beingconsidered. Two dielectric relaxations in addition to a water-inducedone were observed in the frequency range of 1 MHz to 3 GHz, whichpersist throughout the synthesis processes. It is suggested that thelower-frequency relaxation is ascribed to interfacial polarization and thehigher-frequency one is caused by the orientational polarization of theion pair consisting of a counterion and a surfactant polar group. Thelatter and water-induced relaxations were found to be barely changed during the synthesis processes, while the former changesobviously with synthesis time. The evolution of the lower-frequency relaxation and direct current conductivity with synthesis timeare presented and discussed, on the basis of which the particle formation process is inspected from a dielectric spectroscopic point ofview

Automated summary

In-situ monitoring of microemulsion-based nanoparticle synthesis is crucial for understanding the effects of interfacial polarization and orientational polarization during the synthesis process. This study used dielectric spectroscopy to monitor the relaxation behavior of silica nanoparticles synthesized in a CTAB/n-hexanol/cyclohexane/ammonia microemulsion, and found significant changes in the lower-frequency relaxation with synthesis time.