Nanoparticle Semiconductors-Polymer Systems

Production of metal and semiconductor nanoparticles in polymer systems. Dendrimers are used for the synthesis of metallic nanoparticles via dissolution of a metal precursor in a supercritical fluid followed by reduction. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

One of the points made in Schwenz and Moore was that the physical chemistry laboratory should better reflect the range of activities found in current physical chemistry research. This is reflected in part by the inclusion of modem instrumentation and computational methods, as noted extensively above, but also by the choice of topics. A number of experiments developed since Schwenz and Moore reflect these current topics. Some are devoted to modem materials, an extremely active research area, that I have broadly construed to include semiconductors, nanoparticles, self-assembled monolayers and other supramolecular systems, liquid crystals, and polymers. Others are devoted to physical chemistry of biological systems. I should point out here, that with rare exceptions, I have not included experiments for the biophysical chemistry laboratory in this latter category, primarily because the topics of many of these experiments fall out of the range of a typical physical chemistry laboratory or lecture syllabus. Systems of environmental interest were well represented as well. 

The coupling of semiconductor nanocrystals to, for example, small particles of metals [125] or insulators [126,127], is beyond the scope of this chapter In addition, the coupling of semiconductor nanoparticles to DNA [128-133] and to other biological systems [134—140], as well as to organic [141] or metal-organic fluoro-phores [142] and functional polymers [143], have been excluded at this point, so that the literature can be more clearly arranged. 

Arrested precipitation denotes a technique where a poorly soluble product is precipitated within a template by mixing solutions of the respective ions. The template might be a microemulsion, surface ligand solution, mesoporous material (e.g., anodised alumina), polymer or dendrimer, or any other system that provides a confined space for the precipitation. Historically, arrested precipitation was the first method used to synthesise semiconductor nanoparticles that were used to study quantum size effects systematically [33] (and thus paved the way for the whole field of nanosciences). 

D nanomaterial composites — Three dimensions of the nanoparticle fillers are on the nanometer scale. These fillers are also called isodimensional nanoparticle composites. Examples include silica obtained by in-situ sol-gel methods, semiconductor nanoclusters that are dispersed in polymers, and systems in which polymers are subsequently polymerized around nanostractures. 

Fiber-reinforced systems have been modeled with use of an MC method to place parallel fibers into a polymer matrix, with a finite element algorithm (FEA) then being used to compute elastic properties (274). A generic meshing algorithm for use in FEA studies of nanoparticle reinforcement of polymers has been developed (275) and applied to the calculation of mechanical properties of whisker and platelet filled systems. The method should be applicable to void-containing low dielectric materials of such great utility in the semiconductor industry. 

Metal/polymer nanocomposites can have many other important apphcations. For example, nanoparticles embedded into poly(vinylpyrrolidinone) can be used for the electroless plating of polymeric, ceramic, and semiconductor substrates (93-98). These materials have also been used for the preparation of smart systems that experience a reversible alteration of their properties upon exposure to light. They are used as infrared barriers against exposures to intense solar hght or fires (99). 

In a similar manner, several nanoparticles have been produced in the presence of block copolymers in selective solvents so as to form micelles that encapsulate particles such as metal salts. Consequently, these micelles are chemically converted to finely disperse colloidal hybrid polymer/metal particles with interesting catalytic, non-linear optic, semiconductor and magnetic properties [1, 20]. Finally, another area of potential application of amphiphilic block copolymers is that involving surface modification through the adsorption of block copolymer micelles or film formation. The use of a suitable micellar system allows for the alteration of specific surface characteristics, such as wetting and biocompatibility, or even enables the dispersion and stabilisation of solid pigment particles in a liquid or solid phase [1, 178]. 

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