Polymer Colloids and Their Metallation
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Polymer colloids with metal nanoparticles is a fast-developing field of nanoscience and nanotechnology as encapsulation of metal inside the polymer—or, vice versa, formation of polymer inside the nanocomposite colloids—show a promise for exciting applications: catalytic, optical, magnetic. Metal or semiconductor nanoparticles can be 1) formed inside the polymer colloids (block copolymer micelles, dendrimers, or other functionalized polymer colloids) 2) positioned on the outer surface of the polymer colloids; or 3) polymer layer can be formed or adsorbed on the preformed nanoparticle surface. This entry discusses the above routes to prepare polymer nanocomposite colloids considering possible advantages and disadvantages of different methods. The major methods to characterize composition and structure of these nanomaterials include those used for polymer colloid characterization and metal nanoparticle assessment. Some methods allow gathering information on both polymer and nanoparticle structure; some methods are very specific for nanoparticle characterization. Transmission electron microscopy (TEM) is widely used to characterize both polymer colloids and metal (semiconductor) nanoparticles; the latter especially provide high electron contrast. High-resolution TEM (HRTEM) is used to determine the sizes of small particles and to characterize their inner structure. X-ray diffraction (XRD) is used for crystalline nanoparticles to determine their structure and mean particle size. Scattering techniques, small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS), can be used both for polymer colloid and nanoparticle assessment. The latter is possible if polymer structure does not change after particle formation so scattering from polymer particles can be subtracted. If this is not the case, anomalous SAXS is employed because it allows one to establish nanoparticle size and particle size distribution independently of changes in the nanostructured polymer. Spectroscopic techniques are often used to characterize nanoparticles because properties are dependent on nanoparticle size (Au, Ag, semiconductor nanoparticles). In the sections below, examples of polymer colloid and nanoparticle characterization are presented.