Zhao Yanlin, Wang Mi, Hammond Robert B
Institute of Particle Science and Engineering, School of Process, Environmental and Materials Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
J Nanosci Nanotechnol. 2013 Feb;13(2):808-12. doi: 10.1166/jnn.2013.6091.
The nano-particles in colloidal dispersions usually carry an electrical charge and have an electrical double layer associated with their surfaces, however, while remaining electrically neutral overall. Under the effect of an external electric field, the electrical double layer is deformed or in other words, the suspension is polarized. The mechanism of electrochemical polarization is partially dependent on the surface charge and the size of particles. It is known that properties of nano-particles in suspensions may affect the colloids' electrical-impedance spectroscopic properties, e.g., the complex impedance, complex permittivity, complex conductivity, relaxation frequency, and phase angle. However, reports on colloids' electrical-impedance spectroscopic properties are very limited in the current literature. In this paper a simple system, aqueous silica suspensions, was studied using electrical impedance spectroscopy (EIS). A series of experiments were designed to reveal the effect of particle size on the electrical impedance spectra of silica suspensions. The size effect was studied on silica suspensions with the same concentration (10.0 wt%) but different principle particle size (12 nm, 35 nm, 70 nm, 90 nm and 220 nm). The EIS results show that the relaxation frequency decreased with increasing of particle size. This tendency is explained by the polarization effect of electrical double layer and two dispersion mechanisms were analysed in this study. The results provide supportive information for on-line characterisation of nano-particles using electrical impedance spectroscopy.
胶体分散体中的纳米颗粒通常带有电荷，其表面存在双电层，不过整体仍保持电中性。在外部电场的作用下，双电层会发生变形，或者说，悬浮液会被极化。电化学极化的机制部分取决于表面电荷和颗粒大小。已知悬浮液中纳米颗粒的性质可能会影响胶体的电阻抗光谱性质，例如复阻抗、复介电常数、复电导率、弛豫频率和相角。然而，当前文献中关于胶体电阻抗光谱性质的报道非常有限。本文使用电阻抗光谱法（EIS）研究了一个简单的体系——二氧化硅水悬浮液。设计了一系列实验来揭示粒径对二氧化硅悬浮液电阻抗谱的影响。对具有相同浓度（10.0 wt%）但不同主粒径（12 nm、35 nm、70 nm、90 nm和220 nm）的二氧化硅悬浮液进行了粒径效应研究。EIS结果表明，弛豫频率随粒径增大而降低。这种趋势可以通过双电层的极化效应来解释，并且在本研究中分析了两种分散机制。这些结果为使用电阻抗光谱法对纳米颗粒进行在线表征提供了支持性信息。
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