Eur. Phys. J. AP
Volume 12, Number 2, November 2000
|Page(s)||93 - 98|
|Published online||15 November 2000|
Detection of aggregates in magnetic colloids
Department of Electronic and Electrical Engineering, Trinity College, Dublin 2, Ireland
2 Department of Chemistry, University College of North Wales, Bangor LL57 2UW, UK
Corresponding author: email@example.com
Revised: 21 September 2000
Accepted: 21 September 2000
Published online: 15 November 2000
The toroidal technique is used in the determination of the complex, frequency dependent magnetic susceptibility, , of four magnetic fluids consisting of colloidal suspensions of magnetite in water with corresponding saturation magnetisation of 134 G, 107 G, 90 G and 30 G. Plots of the susceptibility components against f (Hz) over the frequency range 10 Hz to 1 MHz, are shown to have approximate Debye-type profiles with the presence of Brownian relaxation being indicated by the frequency, fmax, of the maximum of the loss-peak in the profiles. Corresponding calculations of particle hydrodynamic radius indicate the presence of aggregation. An estimate of the aggregate size distribution in the samples is determined by fitting the measured susceptibility profiles to susceptibility profiles generated by the Debye equations modified by Frohlich, Cole-Cole, Normal and Lognormal distribution functions. The fits obtained from the four fitting functions are found to be similar and thus it is concluded that none of these functions offers any particular advantage over the other functions.
PACS: 75.50.Tt – Fine-particle systems / 75.50.Mm – Magnetic liquids / 76.60.Es – Relaxation effects
© EDP Sciences, 2000
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