Cryochemical synthesis nanoparticles

Simultaneous evaporation of metal with organic and inorganic substances followed by vapor deposition on a substrate allows the production of composite films containing M nanoparticles stabilized in various dielectric matrices [2, 28]. The use of monomer molecules in this process polymerizing during deposition or as a result of the subsequent reactions yields polymeric nanocomposite films with metal inclusions [2, 3, 28, 37]. The new low-temperature synthesis of polymeric nanocomposite films has been elaborated recently. This synthesis is based on the deposition of M/SC and monomers vapors at temperature 80 K followed by low-temperature solid-state polymerization of obtained films in conditions of frozen thermal movement of molecules (cryochemical synthesis) [2], This synthesis has important features, which will be considered further. 

Composite PPX PbO films produced by PVD cryochemical synthesis are sensitive sensors on humidity. The conductivity of the PPX film containing 10 vol.% of PbO nanoparticles sharply increases with the rise of air humidity. The influence of water vapors on the film conductivity is reversible at replacement of humid air on dry one the conductivity comes back quickly to an initial value for dry air and direct and reverse response times are 10 15 sec [89]. 

Resolvation may precede the preparation of polymer-immobiUzed nanoparticles. For example, the cryochemical synthesis of colloidal Ag particles is performed in acetone, which is then replaced by formamide. This dispersion is stable for a few days. The system Ag (2-5 nm) formamide is used as a solvent in the preparation of crosslinked polyacrylamide gel. Three dilferent synthetic resolvation methods are documented. In the first version, a Co-nonadecane system obtained by the cryochemical method was mixed with a solution of a polymer in nonadecane with subsequent sonication. In the second version, the nanoparticles of Co or Ni in toluene were added to a solution of low-pressure polyethylene (LPPE) in toluene at 363K. The third variant employs a toluene polymer solution cooled fi om 383K to 185K. The resulting gel-like system was mixed with nanoparticles obtained cryochemically and subjected to sonication. These techniques make it possible to virtually preclude the aggregation of particles at aU intermediate stages. However, along with the peptization and resolvation, more complex interactions of nanoparticles with the solvent may take place. 

Films of pure PPX and PPX composites with nanoparticles of various metals resulted from cryochemical solid-state synthesis were studied by the dielectric spectroscopy method [104], Dielectric spectroscopy has proven very useful for studying the structure and dynamics of polymer materials as well as the transport mechanism of charge carriers. To study features of the polymer structure dielectric test methods were used due to their high sensitivity to morphological changes. 

Inorganic nanoparticles such as metal/semiconductors (M/SC) immobilized in polymer matrices have attracted considerable interest in recent years due to their distinct individualistic and cooperative properties [84]. Although the control of size and shape of M/SC nanoparticles has been widely investigated, the fundamental mechanism of nanostructural formation and evolution is still poorly understood. A novel cryochemical solid-state synthesis technique has been developed to produce M/SC nanocomposites [85]. This method is based on the low-temperature cocondensation of M/SC and monomer vapors, followed by the low-temperature solid-state polymerization of the cocondensates. As a result of the method of stabilizing the metal particle without requiring any specific coordination bonds between the particle surface and the polymer matrix, generated nanoparticles (Ag-nanocrystal mean size 50 A) were embedded in the polymer matrix with well-controlled shapes and a narrow size distribution [86]. 

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