Composite with Other Nanoparticles

In the nanotechnology field, carbon-based materials and associated composites have received special attention both for fundamental and applicative research. In the first kind, carbon compounds may be included, often taking the form of a hollow spheres, ellipsoids, or mbes. Spherical and ellipsoidal carbon nanomaterials are referred to as fullerenes, while cylindrical ones are called nanombes and nanofibers. In the second class, one includes composite materials that combine carbon nanoparticles with other nanoparticles, or nanoparticles with large bulk-type materials. The unique properties of these various types of nanomaterials provide novel electrical, catalytic, magnetic, mechanical, thermal, and other features that are desirable for applications in commercial, medical, military, and enviromnental sectors. This is the case for conducting polymers (CPs) and carbon nanombes (CNTs) [1-5]. 

Another point is that one can obtain not only diluted systems with low filler content, and can investigate the properties of noninteracting particles in polymer matrix but also highly filled composites with interacting nanoparticles. These can be synthesized and the cooperative behavior of interacting particles studied. The ability to obtain composites with threshold properties ranging from noninteracting to cooperative is another distinctive feature of such systems which will be discussed in Sect. 3. The peculiarity of polymer nanocomposites in comparison with other nano-size objects consists of the influence of polymer matrix on properties of the comp< ite and of the interaction whidi may take place between the matrix and nanoparticle. 

Nanoparticles combined with other nanoparticles of other materials or with larger bnlk-type materials are termed as composites. Nanoparticles, such as nanosized clays, have already been added to prodncts ranging from anto parts to packaging materials to enhance their mechanical, barrier, thermal, and flame-retardant properties. 

PtRu nanoparticles can be prepared by w/o reverse micro-emulsions of water/Triton X-lOO/propanol-2/cyclo-hexane [105]. The bimetallic nanoparticles were characterized by XPS and other techniques. The XPS analysis revealed the presence of Pt and Ru metal as well as some oxide of ruthenium. Hills et al. [169] studied preparation of Pt/Ru bimetallic nanoparticles via a seeded reductive condensation of one metal precursor onto pre-supported nanoparticles of a second metal. XPS and other analytical data indicated that the preparation method provided fully alloyed bimetallic nanoparticles instead of core/shell structure. AgAu and AuCu bimetallic nanoparticles of various compositions with diameters ca. 3 nm, prepared in chloroform, exhibited characteristic XPS spectra of alloy structures [84]. 

The formation of ethylcellulose nanoemulsions by a low-energy method for nanoparticle preparation was reported recently. The nanoemulsions were obtained in a water-polyoxyethylene 4 sorbitan monolaurate-ethylcellulose solution system by the PIC method at 25 °C [54]. The solvent chosen for the preparation of the ethylcellulose solution was ethyl acetate, which is classed as a solvent with low toxic potential (Class 3) by ICH Guidelines [78]. Oil/water (O/W) nanoemulsions were formed at oil/ surfactant (O/S) ratios between 30 70 and 70 30 and water contents above 40 wt% (Figure 6.1). Compared with other nanoemulsions prepared by the same method, the O/S ratios at which they are formed are high, that is, the amount of surfactant needed for nanoemulsion preparation is rather low [14]. For further studies, compositions with volatile organic compound (VOC) contents below 7 wt% and surfactant concentrations between 3 and 5 wt% were chosen, that is, nanoemulsions with a constant water content of 90% and O/S ratios from 50 50 to 70 30. 

The shape of the microcapsules is usually that of the encapsulated substance and the cover thickness depends on the microencapsulation conditions and is varied according to the intended uses of the products. It may be possible to process the resulting composition directly into goods (e.g. by pressing), or the polymeric cover may enable better combination of the nanoparticles with other polymers. 

Others have formed PANl-polystyrene core-shells and hollow spheres using chemical polymerization and decorated them with Au nanoparticles [84] (Figure 14.7). These composites were found to have improved conductivity over undecorated polymer nanoparticles. These were used to investigate dopamine oxidation using cyclic voltammetry. The peak oxidation potential was reduced due to the presence of the Au and the amperometric responses were increased significantly over Au nanoparticle or PANI-modified films alone, most likely due to the distribution of the Au nanoparticles and associated improvements in dopamine diffusion and access to the Au nanoparticle surfaces (Figure 14.8). 

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