Synthesized metal-polymer film

PHYSICOCHEMICAL PROPERTIES OF SYNTHESIZED METAL-POLYMER FILM MATERIALS... 

Polymer film electrodes are prepared either by evaporation technique or by -> electropolymerization. Redox polymers that are usually synthesized chemically are dissolved in a suitable solvent, placed as a droplet on the surface of a metal (or dip-coating, spin-coating techniques are applied) and the solvent is subsequently left to evaporate. The electrode can be used in other solvents in which the polymer is insoluble. Conducting polymer layers are usually developed by electropolymerization directly on the surface of the metal. 

In Scheme 1, octahedral coordination of central metals may lead to a three-dimensional polymer (22). In order to prevent the formation of this polymer and to prepare selectively a linear polymer, a special area for the reaction, such as the interspace of layer compounds or an organic monolayer film, is used. Kanda et al.19) synthesized the polymer in the organic monolayer film prepared by spreading a ligand solution on the surface of an aqueous solution containing metal ions. 

Although most metal-containing polythiophenes have been synthesized by electropolymerization on an electrode surface, there are many reasons to chemically synthesize these polymers. Chemical synthesis may allow isolation of soluble polymers, enabling complete solution characterization (GPC, light scattering, NMR, etc.) and facilitating conductivity studies. Moreover, it can enable improved thin-film preparation and film deposition onto nonconducting substrates. Finally, monomers that are unsuitable for electropolymerization may be polymerized by chemical methods. 

However the material obtained was an unprocessable powder. Unlike substituted polyacetylenes, polyacetylene is insoluble, infusible and unstable in air. The discovery of a technique to synthesize the polymer in the form of a free-standing film and the use of electron donors and acceptors to dope it to have metallic conductivity produced intense interest in the polymer in the last two decades. A wide variety of catalyst systems has been described for the polymerization of acetylene. Besides the route via acetylene polymerization, polyacetylene can also be obtained by a two-step route which involves the synthesis of soluble polymer precursors, which are converted to polyacetylene via thermal elimination and transition-metal-catalysed isomerization, as well as by polymerization of cyclooctatetraene , by dehydrochlorination of poly(vinyl chloride) and by dehydration of poly(vinyl alcohol)... 

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. 

Adsorbed molecules or ions formed during the various syntheses of colloidal metals have been observed by SERS. A silver hydrosol prepared by ferrous reduction of Ag in the presence of citrate showed enhanced Raman intensity corresponding to adsorbed citrate, [213] and gold colloids prepared from [Au(CN)2]" by reduction with borohydride showed SER bands due to adsorbed CN". [214] The Raman spectrum of [Pt(CN)4] adsorbed on a 1.6 nm platinum colloid has been measured, [215] but it was concluded that the slight intensity increase observed (a factor of 7) for the CN mode at 2215 cm might be due to other enhancement mechanisms. It has also been shown that ligands such as (N-4-dimethylaminoazobenzene-4 -sulfonyl)aspartate [216] adsorbed on colloidal silver are highly Raman active as a result of this phenomenon. Polymer films con-... 

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