Structure and dielectric properties of a thermoplastic blend containing dispersed metal

In the present work broadband dielectric relaxation spectroscopy measurements were employed to investigate the dielectric properties of polymer composites. A polyethylene/polyoxymethylene (PE/POM) thermoplastic blend was used as a matrix, while the inclusions were iron (Fe) particles. For comparison, the two pure polymers- PE and POM- were used as a matrix, too. In the PE/POM-Fe composites, the polymer matrix is two-phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. In PE-Fe and POM-Fe composites, the filler spatial distribution is random. The behaviour of all the composites studied is described in terms of the percolation theory. The PE/POM-Fe composites, based on the PE/POM blend, demonstrate different electrical behaviour compared to that of POM-Fe and PE-Fe systems. The percolation threshold value of the PE/POM-Fe composites was found much lower than that of the other two systems. The results were related to the microstructure of the composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behaviour of the PE/POM-Fe composites by taking into account the ordered distribution of the filler particles in a binary polymer matrix. Optical microscopy photographs confirm this model.     

Water sorption and electrical/dielectric properties of organic-inorganic polymer blends

Organic-inorganic polymer blends (OIPB) were obtained by reaction of organic and inorganic oligomers. The organic oligomer was synthesized with 2,4-toluene diisocyanate (TDI) and oligooxypropylene glycols (OPG) with various molecular weights (MW). The inorganic component was a water solution of sodium silicate. The OIPB obtained are hydrophilic and have great water sorption ability (the relative weight of sorbed water reaches 2000 %). The kinetics of water sorption and the changes of electrical conductivity during sorption were studied. Sorption ability, and mechanical, electrical and dielectric properties of OIPB depend on molecular weight of OPG: conductivity increases with increasing MW, whereas the sorption ability correlates with the mechanical properties. The influence of the inorganic phase content on the electrical and dielectric properties was studied as well.     

Structure‐dependent conductivity and microhardness of metal‐filled PVC composites

Metal‐filled composites of a commercial PVC (polyvinyl chloride) powder (mean particle size d_p ≈ 100 microns) and a metal powder (mean particle size d_f about 100 microns for copper, Cu, and about 10 microns for nickel, Ni) prepared by mechanical mixing in a ball mill, subsequent hot‐pressing at 443 K and rapid cooling to 300 K, were characterized by the room‐temperature measurements of electrical conductivity σ, density ρ and microhardness H. The sudden jumps of about 17 orders of magnitude followed by a much slower growth up to the limiting filler fraction ϕ* on the log σ vs. ϕ plots are the evidence for the onset of percolation transitions, at filler volume contents ϕ_c1 = 0.05 and 0.04 for PVC/Cu and PVC/Ni, respectively. For both systems, the values of H exhibited an initial steep increase up to ϕ_c2 = 0.07, followed by an apparent plateau extending up to ϕ = 0.18. However, drastic differences in the patterns of composition dependence of H were observed at higher metal loadings, i.e., a continuous increase of H up to the leveling‐off at ϕ* for PVC/Cu, in contrast to a sudden drop of H at ϕ = 0.20 and subsequent slow increase for PVC/Ni. For both composites the apparent density ρ′ of a polymer matrix remained the same as that of the neat PVC in the composition interval ϕ < 0.20, while at ϕ* > 0.20 a precipitous drop of ρ₁ was observed due to the formation of polymer‐free voids between filler particles (crowding effect) as ϕ approaches ϕ*. The observed effects were analyzed in terms of a tentative model envisaging cross‐overs from “dilute suspension regime” to “semi‐dilute suspension regime” in the concentration range ϕ_c1 to ϕ_c2, and from “semi‐dilute suspension regime” to “concentrated suspension regime” above ϕ = 0.20. Different behavior in this latter regime was explained by intrinsic differences in the structure of conductive infinite clusters between mixtures of particles of about the same size (PVC/Cu) and of widely different sizes (PVC/Ni).