Magnetodielectric Response of Soft Magnetoactive Elastomers: Effects of Filler Concentration and Measurement Frequency

Abstract

The magnetodielectric response of magnetoactive elastomers (MAEs) in its dependence on filler concentration, magnetic field, and test frequency is studied experimentally. MAEs are synthesized on the basis of a silicone matrix filled with spherical carbonyl iron particles characterized by a mean diameter of 4.5 µm. The concentration of the magnetic filler within composite materials is equal to 70, 75, and 80 mass%. The effective lossless permittivity ε′ as well as the dielectric loss tanδ grow significantly when the magnetic field increases. The permittivity increases and the dielectric loss decreases with increasing filler concentration. In the measurement frequency range between 1 kHz and 200 kHz, the frequency hardly affects the values of ε′ and tanδ in the absence of a magnetic field. However, both parameters decrease considerably with the growing frequency in a constant magnetic field. The more strongly the magnetic field is applied, the larger the change in permittivity and loss tangent at the same test frequency is observed. An equivalent circuit formulation qualitatively describes the main tendencies of the magnetodielectric response.

Dielectric Spectroscopy of Hybrid Magnetoactive Elastomers

“…However, some other phenomena have also attracted much attention. Among them are magnetodeformational effect [ 13 , 14 , 15 , 16 , 17 , 18 ], i.e., significant deformations of MAE samples in homogeneous and gradient or alternating magnetic fields, magnetodielectric effect as well as magnetoresistance of MAEs [ 19 , 20 , 21 , 22 , 23 ], i.e., a tremendous increase in both relative permittivity and conductivity of samples in homogeneous magnetic fields. Furthermore, MAEs demonstrate magnetically controlled radio-absorbing properties [ 24 , 25 , 26 ] that are promising for the design of magneto-controllable radio-shielding or polarizing covers on their basis.…”

“…It should be mentioned that the magnetodielectric effect (MDE) and magnetoconductivity of MS and MH MAEs in an applied magnetic field have been previously studied in a number of publications [ 19 , 20 , 21 , 22 , 23 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. Within the general approach, the value of MAE permittivity can be obtained from the measurements of the capacity of a capacitor filled with an MAE [ 22 , 23 , 40 , 41 , 42 ]. A strong increase in the capacitance was observed when the magnetic field was applied perpendicular to the capacitor plates [ 40 , 41 ].…”

“…A strong increase in the capacitance was observed when the magnetic field was applied perpendicular to the capacitor plates [ 40 , 41 ]. At a fixed distance between the capacitor plates during measurements, the capacitance change characterizes a change in the effective permittivity of the material caused by filler re-arrangements within the polymer matrix [ 22 , 23 , 41 ]. The effect of the type of magnetic filler, as well as the size and concentration of magnetic particles within composites, was studied in [ 22 ].…”

“…The largest MDE of the order of 1000% in the magnetic field of 0.57 T was reported for MAEs based on silicone matrix containing 75wt% of CI [ 41 ]. Simple theoretical models [ 22 , 23 , 48 ] as well as computer simulations [ 49 ] confirm that MDE originates from the restructuring of the magnetic filler within a soft elastomer matrix. The recently developed theoretical approach [ 50 ], based on the effective medium approximation with the account of field-dependent restructuring of the filler, described the observed magnetodielectric phenomena in MAEs rather well.…”

Electrorheological Properties of Polydimethylsiloxane/TiO2-Based Composite Elastomers

“…As a rule, the electrorheological effect for structured elastomers is greater than for materials with a stochastic distribution of filler particles, which is associated with the smaller distance between the particles of the disperse phase. Anisotropically-filled elastomers are also characterized by a higher dielectric constant and Maxwell–Wagner dispersion [ 32 , 33 , 34 ].…”