Conductivity, magnetic fillers

Closed-form expressions from composite theory are also useful in correlating and predicting the transport properties (dielectric constant, electrical conductivity, magnetic susceptibility, thermal conductivity, gas diffusivity and gas permeability) of multiphase materials. The models lor these properties often utilize mathematical treatments [54,55] which are similar to those used for the thermoelastic properties, once the appropriate mathematical analogies [56,57] are made. Such analogies and the resulting composite models have been pursued quite extensively for both particulate-reinforced and fiber-reinforced composites where the filler phase consists of discrete entities dispersed within a continuous polymeric matrix. 

For many applications of filled polymers, knowledge of properties such as permeability, thermal and electrical conductivities, coefficients of thermal expansion, and density is important. In comparison with the effects of fillers on mechanical behavior, much less attention has been given to such properties of polymeric composites. Fortunately, the laws of transport phenomena for electrical and thermal conductivity, magnetic permeability, and dielectric constants often are similar in form, so that with appropriate changes in nomenclature and allowance for intrinsic differences in detail, a general solution can often be used as a basis for characterizing several types of transport behavior. Useful treatments also exist for density and thermal expansion. 

The incorporation of a variety of semiconducting, conducting, dielectric, and magnetic filler materials (e.g., another CP/ICP, QCNs, nanoparticu-... 

The specific volumetric electric resistance of the polymer films obtained with using of described above method was changed in the interval 10-50 kOhm.sm. The selection of such interval of the composite resistance was dictated by preliminary selection of conducting composites effectively reacted on the mechanical deformations. The composites contained the magnetic filler are characterized simultaneously both electrical and magnetic properties. 

Incorporating reinforcing particles that respond to a magnetic field is important with regard to aligning the particles to improve mechanical properties anisotropically [223-226]. In related work, some in-situ techniques have been used to generate electrically conducting fillers such as polyaniline within an elastomeric material [227],... 

This technique could be combined with the in situ approach by generating metal or metal oxide magnetic particles in a magnetic field,75,76 for example by the thermolysis or photolysis of a metal carbonyl. As mentioned earlier, some related work involved the use of in situ techniques to generate electrically conducting fillers such as polyaniline within PDMS.28... 

Composites with filler concentrations close to the percolation threshold exhibit conductivity which is sensitive to compressive deformation, since this brings the metal particles into contact, thereby forming percolation pathways. This sensitivity has been exploited especially in anisotropic composites. These are made by prealigning the metal particles with either electric or magnetic fields. This alignment is identical with that produced by external fields in electro- and magneto-rheological fluids where at a critical field continuous threads of... 

Electroless deposition offers an attractive way of producing various fillers with a conductive surface or desirable magnetic properties, which can further be used in the production of composite materials with dielectric matrices for electromagnetic shielding. 

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