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Structure‐dependent conductivity and microhardness of metal‐filled PVC composites
Author(s) -
Mamunya Yevgen P.,
Privalko Eleonora G.,
Lebedev Eugene V.,
Privalko Valery P.,
Calleja Francisco J. Balta,
Pissis Policarpos
Publication year - 2001
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/1521-3900(200105)169:1<297::aid-masy297>3.0.co;2-z
Subject(s) - materials science , composite material , polyvinyl chloride , indentation hardness , metal , volume fraction , nickel , percolation threshold , copper , electrical resistivity and conductivity , microstructure , metallurgy , engineering , electrical engineering
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 ρ 1 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).