Theoretical method for calculation of effective properties of composite materials with reconfigurable microstructure: Electric and magnetic phenomena

Abstract

We propose a theoretical approach for calculating effective electric and magnetic properties of composites with field-dependent restructuring of the filler. The theory combines the Bruggeman-Landauer approximation extended to a field-dependent (variable) percolation threshold with the approximate treatment of nonlinearity of material properties. Theoretical results are compared with experiments on magnetorheological elastomers, which in the context of investigated phenomena are often called magnetoactive elastomers (MAEs). In MAEs with soft polymer matrices, the mutual arrangement of inclusions changes in an applied magnetic field. This reorganization of the microstructure leads to unconventionally large changes of electrical and magnetic properties. Obtained theoretical results describe observed phenomena in MAEs well. Qualitative agreement between theory and experiment is demonstrated for the magnetodielectric effect. In the case of magnetic permeability, quantitative agreement is achieved. The theoretical approach presented can be useful for development of field-controlled smart materials and design of smart structures on their basis, because the field dependence of physical properties can be predicted.

Efficient Chain Formation of Magnetic Particles in Elastomers with Limited Space

“…The distance between the nearest neighbor beads was calculated to be 31 μm. Magnetic particles are forced to be localized in the vacancy and form a chain structure by the magnetic field, for example, a qualitative representation of the microstructure [17] and computed tomography images [18]. In our previous study, the storage modulus for bimodal magnetic elastomers containing small nonmagnetic particles (1.4 or 10.6 μm in diameter) gradually increased with the volume fraction of nonmagnetic particles, and a clear percolation threshold was not observed.…”

Effective Medium Theory for the Elastic Properties of Composite Materials with Various Percolation Thresholds

“…The particular concentration value, where the maximum change in behavior of the effective modulus occurs, is shifted towards concentrations smaller than 1/2. Note that analogous situation occurs for the effective electrical conductivity, which has been studied in detail in [49]. Figure 7 compares the results of the EMT with experimental results of [53].…”

“…In Ref. [49] we introduced the method of the moveable (field-dependent) percolation threshold and employed the modified EMT (18)- (19) for describing the significant changes of dielectric and magnetic properties of the magnetoactive elastomers in an external magnetic field.…”

Thermoresponsive Conductivity of Acrylamide-based Polymers and Ni Microparticle Composites

“…For example, crystalline polymer-based composites including Ni microparticles (NiMPs) exhibit thermoresponsive conductive function which is named as PTC phenomena regarding resistivity. [6][7][8] The materials are conductive around room temperature, and turn to insulators at high temperature. The temperature when the resistivity is 10 times as large as that at room temperature is defined as TPTC.…”

“…This is because the aggregation forms of NiMPs would be change at that time (Scheme 1b). 7 Owing to the mechanism, it is difficult to tune the temperature at which the conductivity changes. To resolve the problem, the aggregation of NiMPs in matrix will be changed by other factors except for the volume expansion around Tm.…”