Dielectric relaxation in concentrated nonaqueous colloidal suspensions

• Published in: Journal of colloid and interface science Vol. 436; no. 436; pp. 132 - 137
• Main Authors: Ramos, M.M., Perea, R., Delgado, A.V., Arroyo, F.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.12.2014; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Colloids; Derivatives; Dielectric constant; Dielectric dispersion; Dielectric relaxation; Double layer; Electrodes; Exact sciences and technology; Frenkel–Trukhan; General and physical chemistry; Goethite; Interfacial polarization; Mathematical models; Nonaqueous suspensions; Permittivity; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Silicone oil; Solid-liquid interface; Surface physical chemistry; Dielectric dispersion; Nonaqueous suspensions; Frenkel–Trukhan; Interfacial polarization; Goethite; Silicone oil; Polarization; Colloidal suspension; Frenkel-Trukhan; Interface; Concentrated suspension; Dielectric relaxation
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2014.09.008

[Display omitted] •We measure the permittivity of elongated goethite particles in silicone oil.•The log-derivative method is adequate to correct electrode polarization.•Both the relaxation amplitude and critical frequency increase with volume fraction.•The relaxation frequency is higher than predicted by Maxwell–Wagner theory.•Frenkel–Trukhan model can explain our experimental results. In this work we report on the permittivity of suspensions of elongated goethite particles in silicone oils of different viscosities. In spite of the low conductivity of the systems, the electrode polarization is significant. To correct this phenomenon, the procedure chosen is the one called logarithmic derivative of the real part of the permittivity, and it proves to efficiently reduce the effect of electrodes to the extent that the spectra of pure liquids are flat in the accessible frequency range (20Hz–1MHz). In our suspensions, we observe the presence of a dielectric relaxation for frequencies in the range 4–40kHz. In principle, such relaxations might be ascribed to the Maxwell–Wagner (MW) polarization. However, it is found that both the characteristic frequency and the relaxation amplitude of the suspensions increase with volume fraction, something unexpected for an MW relaxation. Such discrepancy can be explained by considering the Frenkel–Trukhan model, which reproduces the Maxwell–Wagner results in conditions of thin electrical double layers (which it is not our case). An excellent agreement is found between our data and the model predictions, using only the particle surface charge as a parameter.