Metal-nanocrystal-containing polymer

Metal-polymer systems obtained as a result of vapor deposition cryochemical synthesis contain stabilized small nonmetallic clusters of metal atoms and metal nanocrystals, but only metal nanocrystals participate in conductivity processes. The data on Ag-containing PPX composites [44] testify to the fact that the relative part of metal stabilized in cluster form at ambient temperature sharply decreases with increasing total metal content even in the range 0-2 vol. %. Therefore, at measurements of conductivity, which were carried out at considerably higher metal concentrations, it was accepted that as a first approximation, all metal is as nanocrystals. 

Polymers Containing Metal Clusters and Nanocrystals Physically Incorporated in Polymer Matrix... 

The cluster aggregation to nanocrystals depends on the metal content. In the obtained Ag-ClPPX films the relative part of metal, stabilized in cluster form at 293 K, decreases from 90% to 20% while increasing the total metal content from 0.25 to 2 vol. % [44]. The stability of clusters is greatly influenced also by the structure of the polymer matrix [36, 44]. Comparison of spectra in Figures 2.5 and 2.6 shows that in cryochemically synthesized films, the Ag-CNPPX stability of Ag clusters is much higher than that in similar films Ag-ClPPX. The data on DJ D )o (see above) in the spectra of various films show that in cryochemically synthesized Ag-CNPPX films heated to ambient temperature, up to 70% from total incorporated Ag (in amount of about 2 vol. %) is stabilized as small noncrystalline clusters [44]. A similar result has been reported in reference 36 for Ag-PPX (Table 2.1). But in Ag-Cl-PPX containing the same total Ag, the fraction of Ag clusters at 295 K is only about 20% [24, 44]. 

When metal particles are isolated in a polymer so that the interaction between them can be neglected, the conductivity of a composite is determined by that of a polymer matrix. In such composites, metal nanoparticles can only inject carriers into a polymer but do not influence substantially the conductivity process [59], This is the case of metal-PPX films prepared by the cryochemical vapor deposition teclmique if such films contain metal or semiconductor nanocrystals in amounts less than 4—5 vol. % [30]. The conductivity of such composites follows classical olmfic current-voltage relationship [30] and Arrheiuus dependence on temperature [57]. At higher metal contents the mechaiusm of conductivity in synthesized composite films changes under influence of the interparficle interaction. In PPX films containing Pb nanoparficles in amounts from 5 to 10 vol. %, the dependence of current I on voltage U looks like In / [30]. This dependence is characteristic for a... 

Cryochemically synthesized PPX films containing metal or semiconductor nanocrystals have a fine porous structure caused by features of solid-state polymerization. Due to this structure, molecules of gaseous substances readily penetrate into polymer film from the environment. Synthesized composite films demonstrate valuable strong sensor effects resulting from a marked influence of some low-molecular-weight molecules, diffusing into the polymer and adsorbed onto nanocrystals, on the film conductivity [4, 30, 62-64]. Such effects are characteristic of films whose conductivity is governed by electron transfer between nanoparticles. 

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