Electrical behaviour dispersion

In low viscosity fluids, considerable effort has been devoted to the dispersion of concentrated suspensions for slip casting or tape casting. In aqueous media it is the electrical behaviour of the solid-liquid interface which is used to preserve dispersion In non-aqueous media dispersion and deflocculation have been achieved by employing strongly polar solvents or by adding surfactants. ... 

By the term particulate composites we are referring to composites reinforced with particles having dimensions of the same order of magnitude. Particulate composites are produced from a polymeric matrix, into which a suitable metal powder has been dispersed, and exhibit highly improved mechanical properties, better electrical and thermal conductivity than either phase, lower thermal expansivity, and improved dimensional stability and behaviour at elevated temperatures. 

Though numerous groups have fabricated CNT-polymer composites, mechanical behaviour has not been the main focus of such studies. The bulk of the work has focused on studying the effect of the addition of CNT on the crystallization behaviour and on the electrical conductivity and improving dispersion by employing different techniques, as described earlier. 

Composites containing metal particles provide a clear example of the percolation behaviour described in Section 8.3. By way of illustration we can cite the results shown in Table 8.1 for a dispersion of approximately spherical nickel particles (about 10 pm in diameter) in a low-density polyethylene. Here conductivity is lost entirely at concentrations below about 20% by volume of metal, corresponding to about 70% by mass. Nevertheless, conductive paints, which are frequently used for painting electrodes on to electrical test specimens and devices, work in just this way. 

It is also shown how x(< ) is related to the temporal behaviour of the dielectric polarization follomng the sudden application, or removal, of an electric field. Various forms of the Kramers-Kronig dispersion relations are introduced for y (o>) and x C") aod for a number of functions of The section closes with the ddOnition of the frequency-dependent complex refractive index n() = n(cu) — and a discussion of its relation... 

Nevertheless the use of dielectric materials obtained by conductive filler dispersion (carbon black, graphite fibres, metallic powders) is limited. As a matter of a fact material performances are dependent on the filler content as well as particle aggregation phenomena. These composites require a high level of reproducibility and their behaviour is linked to the control of electronic inter-particular transfer. The measured parameter (complex permittivity) depends on the texture of the percolation aggregates and consequently on the processing conditions. The percolation threshold (the particle concentration, after which particles are in contact and the electrical current exists) depends on the particle shape (sphere, plates or fibres). 

The flux of metal atoms in vacuum (Pd, Sn, Al, Ti, Zn), evaporated from a bulk sample condenses onto a cooled substrate together with the monomer. The condensate consists of nanoparticles of the metal and the monomer (Fig. 1). Upon heating the substrate to ambient temperature the monomer polymerises to PPX. The structure thus obtained is a porous matrix with dispersed nanoparticles in it. The properties of these nanocomposites containing metal and/or metal-oxide nanoparticles in the polymeric matrix are presented. Manipulation of the synthesis conditions, i.e., the distance between the vapour source and the substrate, the tilt angle of the beam, and the deposition time allowed for optimising the deposition regime. Measuring the electrical resistance of the condensate and composite permitted the control of the film formation in relation to the oxidation behaviour. 

Mineral fillers are compounded with polymers for several purposes which include for mechanical reinforcement, as pigments, for enhancement of electrical properties or for lowering the material costs and thermal behaviour. They have an important role in the polymer due to their ability to fulfill a variety of roles. The use of fillers in polymer compounds provides additional benefits, for instance, the dispersion of the filler during compounding onto a polymer surface prevents delamination. This assures the long-term chemical stability of introduced chains, in contrast to physically coated chains [51-53]. 

In electro-optical measurements, one determines essentially an electrical dipole moment which is related to the number and the spatial distribution of mobile ions in the vicinity of a colloid surface. This technique - light scattering in the presence of an electrical field - was abundantly us in the investigation of the electrical properties of colloids dispersed in water. Extensive monographs on colloid electro-optics were published (7-2). In recent years, the effect of water soluble polymers on the behaviour of hydrosols (especially colloids of mineral or metallic origin) began to raise interest. Polymers partly because of their large... 

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