Ions, adsorption and electric response of a ferrofluid cell

Abstract

We show that the electric response of a cell in the shape of a slab containing a ferrofluids (magnetic particles in kerosene) can be interpreted by means of a model...

Nonlinear behavior of the impedance spectrum of a kerosene based ferrofluid

“…It follows that we can consider a relaxation frequency f R = 2/ τ R . Assuming Λ = 4.73 × 10 −8 m, D = 1.23 × 10 −11 m 2 s −1 , and d = 127 × 10 −6 m, 19 we get f R ∼ 8.2 Hz, and hence log( f R ) ∼ 0.9, in good agreement with the experimental result. In the case considered here of a sinusoidal forcing, we can therefore expect that the ions do not participate in the dynamics of the system, i.e.…”

“…These results are in agreement with some others reported in the literature according to which the impedance is most affected in the lower frequency range. 18,19 The results reported in Fig. (2) suggest that the critical frequency below which the non-linearities due to ionic motion are established in it is quite small.…”

“…(2) shows the real R and the imaginary part w of the impedance Z of a FF sample measured with V 0 = 30 mV, 1, 2 and 3 V. In terms of shape the spectra are all similar to each other and to the spectra of other kerosene-based FF already reported in the literature. 13,18,19,41 All the real parts R increase for decreasing f while in the middle frequency range they have a large plateau until the Debye frequency f D B 800 Hz. In the high frequency limit all R curves decrease with f À2 .…”

“…In the low frequency region, up to 0.3 mHz, the response of the cells depends on the electrodes, as discussed in. 19 To interpret our experimental data we proposed a simple generalization of the Poisson-Nernst-Planck model, based on the equations of continuity for the ions and on the equation of Poisson for the electric potential across the sample, with boundary conditions derived by the Langmuir kinetic equation. This model was in reasonable agreement with our experimental data.…”