Segregated metallic particles polymers

It is also possible to reinforce polymers with metallic particles. D. T. Turner and one of his students observed that good electrical conductivity can be measured even at very low fillings, such as only 6% by volume. Microscopic examinations showed that the metallic particles formed continuous chains segregated around zones of unpenetrated polymer. 

Mixtures of powders of poly(vinyl chloride) (FVC) and various metals were compacted at a pressure of 10,000 psig at 120-130°C. The compacts appear to be strong, and density measurements show the porosity to be <1.5%, Electrical resistivity is reduced, from a value for unloaded FVC of about JO25 Clem, to < JO"1 Clem by a fractional volume loading of nickel or copper as low as 0.06. Microscopic examination of polished sections of the compacts show the metallic particles to be segregated around zones of unpenetrated polymer which correspond in size to the initial particles of FVC. The pattern of segregation favors the formation of continuous chains of metallic particles at unusually low volume loadings. 

A reason for the difference in behavior noted above becomes apparent by comparing photomicrographs of sections. In Gurland s system the particles of silver are distributed more or less randomly throughout the polymer as may be seen from his results quoted in Figure 2. By contrast, in the present system the metallic particles are excluded from certain elements of volume and segregated into others. This was apparent in all... 

The size of the metal particles relative to any structure present in the polymer matrix can also affect the value of pc. Segregated composites have been prepared by compression molding a mixture of metal and polymer particles [35]. When the radius of the polymer... 

Figures 11.3" shows the methods of packing metal particles in a polymer matrix, such as random and segregated distributions. Figure 11.3(a) and (b) refer to the random distribution, below and above critical volume percentage (cpc) of metal filler. In the random packing method, no network formation of metal particles occurs between contiguous sites. In contrast, in the segregated distribution, a network is formed. Figures 11.3(c) and (d) refer to the segregated...

Polymers that phase-separate upon solidification may contribute to segregation of conductive filler to the interphase or to noncrystalline regions. This can produce favorably high conductivities with less metal because of the local concentration of metal partides. This is illustrated in Figure 18.5 [64]. Note two cases when polymer and metal partides are of comparable size (panels a and b) versus small metal particles (pands c and d). Also in Figure 18.5 note the microstructures for V Vc. 

The obtained structures can be isotropic, i.e. the metal nanoparticles segregate in one type of lamellae in onion-like nanoparticles [78-80], form isotropic surface structures [81, 82] (Fig. 6), or can be anisotropic with regard to the particle geometry. The latter case was based on metal nanoparticles/polymer assemblies [81] or similar assemblies but with a fluorescent dye instead of the metal nanoparticles [83]. 

The simplest means to template the placement of metal is to evaporate it onto the proper choice of a copolymer film. For those copolymer blocks with sufficiently disparate metal-polymer interactions, interfacial energies can be used to tailor the ultimate location of metallic particles after coalescence. Segregation of metals into microdomains have been demonstrated in this manner by Jaeger and coworkers [65,66]. While only a limited set of metals satisfy the constraints, metal films so fabrieated would aet as robust masks (Figure 9.7). Most interestingly, chains of such segregated particles lead to fascinating transport properties. 

Conventional polymer-metal composites involve the dispersion of filler in a polymer matrix. Two methods of packing filler particles in a polymer matrix have evolved during the past 30 years "random" distributions and "segregated" distributions. Continuity in the "random" packing method relies on the formation of a network strictly by the chance contact between filler particles as governed by percolation... 

Controlled synthesis of RuPt NPs was made possible by playing with the kinetics of decomposition of the precursors. While the codecomposition of [Ru(COD)(COT)] and [Pt(dba)2l in the presence of PVP as stabilizer led to a RuPt alloy with a fee structure [83,84], core-shell RuPt NPs were obtained in PVP, using [Pt(CH3)2(COD)] (i.e., [dimethyl(l,5-cyclooctadiene)platinum(II)]) instead of [Pt(dba)2] [74], owing to the slower rate of decomposition of [Pt(CH3)2(COD)] (Figure 3.4, top). The chemical segregation leading to core-shell RuPt results from kinetic (decomposition rate of the metal precursors) and thermodynamic (preferred location of each metal in the particle) parameters as well as from the steric properties of the polymer, taking into account that PVP has little or no chemical interaction with metals. Thus, the chemical order within the particles can be controlled via the choice of the metal precursor. 

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