The application of low frequency dielectric spectroscopy to analyze the electrorheological behavior of monodisperse yolk–shell SiO2/TiO2 nanospheres

Abstract

Monodisperse SiO₂/TiO₂ yolk–shell nanospheres (YSNSs) with different SiO₂ core sizes were fabricated and adopted as dispersing materials for electrorheological (ER) fluids to investigate the influence of the gradual structural change of disperse particles on ER properties. The results showed that the ER performance of the YSNS-based ER fluid prominently enhanced with the decrease of SiO₂ core size, which was attributed to the enhancement of electric field force between YSNSs. Combined with the analysis of dielectric spectroscopy, it was found that the increase of permittivity at low frequency (10⁻²–10⁰ Hz) was due to the increase of polarized charges caused by secondary polarization (P_sp). Moreover, the number of P_sp closely related to the distributing change of polarized particles in ER fluid was a critical factor to assess the ER performance. Additionally, a parameter K (the absolute value of the slope of permittivity curves at 0.01 Hz) could be utilized to characterize the efficiency of structural evolution of polarized particles in ER fluid. Compared with the ER performance, it could be concluded that the value of Δε_{(100Hz–100kHz)}′ just demonstrated the initial intensity of the interface polarization in the ER fluid as the electric field was applied, which ignored the distributing evolution of polarized disperse particles in ER fluid. The polarizability Δε_{(0.01Hz–100kHz)}′ obtained in the frequency range of 10⁻²–10⁵ Hz should be more suitable for analyzing the system of ER fluid. The relationships between polarizability of disperse particles, parameter K and ER properties were discussed in detail.