Spherical Nanoparticles

The TEM image of the PVP capped CdSe at 5 hr in figure 6A showed small, spherical particles with some aggregation. The aggregation is due to the oriented attachment between the spherical nanoparticles as a result of dipole-dipole interactions between the highly... 

This study could be extended to the synthesis of iron nanoparticles. Using Fe[N(SiMe3)2]2 as precursor and a mixture of HDA and oleic acid, spherical nanoparticles are initially formed as in the case of cobalt. However, a thermal treatment at 150 °C in the presence of H2 leads to coalescence of the particles into cubic particles of 7 nm side length. Furthermore, these particles self-organize into cubic super-structures (cubes of cubes Fig. ) [79]. The nanoparticles are very air-sensitive but consist of zerovalent iron as evidenced by Mossbauer spectroscopy. The fact that the spherical particles present at the early stage of the reaction coalesce into rods in the case of cobalt and cubes in the case of iron is attributed to the crystal structure of the metal particles hep for cobalt, bcc for iron. 

Enhanced Optical Fields in Spherical Nanoparticle Assemblies and Surface Enhanced Raman Scattering... 

Enhanced electric-field distribution is illustrated schematically in Figure 3.8, based on reported electromagnetic simulations, for a dimer of a noble metal spherical nanoparticle. The optical field enhancement at the gap site occurs only when the incident polarization is parallel to the interparticle axis of the dimer. 

In general, the various synthesis strategies for nanocarbon hybrids can be categorized as ex situ and in situ techniques [3]. The ex situ ( building block ) approach involves the separate synthesis of the two components prior to their hybridization. One can rely on a plethora of scientific work to ensure good control of the component s dimensions (i.e. size, number of layers), morphology (i.e. spherical nanoparticles, nanowires) and functionalization. The components are then hybridized through covalent, noncovalent or electrostatic interactions. In contrast, the in situ approach is a one-step process that involves the synthesis of one of the components in the pres-... 

Fig. 3 Synthesis of spherical nanoparticles showing changes in the sample with time. There was no phase separation observed in the isooctane/AOT (0.8 M)/Lecithin (0.4M)/NaBH4 (0.01 M)/HAuCl4 (0.01 M) sample after 45 days...

Si02 nanoparticles AOT/decane/benzyl alcohol (BA)/water/ammonia (R = 6.8, BA/AOT molar ratio = 0-2.5) TEOS/H20 + NH3 (13.9 wt%) [TEOS] = 0.044 M h = [H20]/[TE0S] = 18.5 Microemulsions with BA/AOT >1.5 became unstable during synthesis reaction nearly spherical nanoparticles maximum in particle size at BA/AOT = 1.5 (32)... 

The procedure to fabricate colloidal silver, (Ag°) , spherical nanoparticles is similar to that already described (see Section 9.3.3) The Cu( AOT)2 is replaced by the silver derivative. The relative concentration of Na(AOT), Ag(AOT)2, and the reducing agent remain the same. Control of the particle size is obtained from 2 nm to 6 nm (67). To stabilize the particles and to prevent their growth, 1 p.l/mL of pure dodecanethiol is added to the reverse micellar system containing the particles. This induces a selective reaction at the interface, with covalent attachment, between thio derivatives and silver atoms (68). The micellar solution is evaporated at 60°C, and a solid mixture of dodecanethiol-coated nanoparticles and surfactant is obtained. To remove the AOT and excess dodecanethiol surfactant, a large amount of ethanol is added and the particles are dried and dispersed in heptane. A slight size selection occurs, and the size distribution drops from 43% to 37%. The size distribution is reduced through the size selected precipitation (SSP) technique (38). 

The synthesis of spherical nanoparticles using the mediated seeded-growth method has been carried out using different mild reducing agents such as citrate, organic acids or hydroxylamine and well-defined monodisperse seed particles. 

Chauve et al. [253] utilized the same technique to examine the reinforcing effects of cellulose whiskers in EVA copolymer nanocomposites. It was shown that larger energy is needed to separate polar EVA copolymers from cellulose than for the nonpolar ethylene homopolymer. The elastomeric properties in the presence of spherical nanoparticles were studied by Sen et al. [254] utilizing Monte Carlo simulations on polypropylene matrix. They found that the presence of the nanofillers, due to their effect on chain conformation, significantly affected the elastomeric properties of nanocomposites. 

The most basic form of MIP nanomaterials is the spherical nanoparticle, obtained by a number of techniques such as microemulsion polymerization [99-101], and polymerization in diluted solutions resulting in nanospheres and microgels [102-106]. Microgels (also sometimes referred to as nanogels) are particularly interesting, since they represent soluble, though cross-linked, MIPs with a size in the low nanometer range, close to that of proteins. 

Very recently the crystallization of non-spherical nanoparticles into ordered arrangements has been observed that had not been seen with spherical particles. Thanks to the high density of DNA on the particle solid faces, hexagonal packing of nanorods, and columnar stacking of nanoprisms, fee crystals of rhombic dodecahedrons were observed in [152] (see Fig. 35). 

The simplest way to classify nanomaterials used in combination with liquid crystal materials or the liquid crystalline state is by using their shape. Three shape families of nanomaterials have emerged as the most popular, and sorted from the highest to the lowest frequency of appearance in published studies these are zero-dimensional (quasi-spherical) nanoparticles, one-dimensional (rod or wirelike) nanomaterials such as nanorods, nanotubes, or nanowires, and two-dimensional (disc-like) nanomaterials such as nanosheets, nanoplatelets, or nanodiscs. 

The nematic phase has unquestionably been the go-to phase to study and understand the major driving forces that govern interactions between suspended, quasi-spherical nanoparticles and liquid crystal molecules or mixtures. We credit this to three important factors (1) early experimental studies [288, 289] based on the foundation of de Gennes very early work on ferronematics [121], (2) the availability of nematic liquid crystals including room temperature and wide temperature... 

In comparison to nematic liquid crystals, examples of smectic liquid crystals doped with quasi-spherical nanoparticles became more elusive over the last few years. This is surprising especially considering recent work by Smalyukh et al., who found that nanoscale dispersion (based on /V-vinyl-2-pyrrolidone-capped gold nanoparticles with 14 nm diameter) in a thermotropic smectic liquid crystal (8CB) are potentially much more stable than dispersions of nanoparticles in nematics [367]. 

It was really only a matter of time until researchers in the field started doping blue phases with quasi-spherical nanoparticles. This area is very much in its infancy, but the few recent reports already show some promising results. Yoshida et al., for example, reported on an expansion of the temperature range of cholesteric blue phases from 0.5 to 5°C by doping blue phases with gold nanoparticles (average diameter of 3.7nm) as well as a decrease in the clearing point of approximately 13°C [427]. A similar effect was also observed by Kutnjak et al. for CdSe quantum dots simultaneously capped with oleyl amine and TOP (diameter of the core 3.5 nm) in CE8 (Merck) and CE6 (BDH). The authors found that particularly blue phase III was stabilized in these mixtures, blue phase II destabilized, and... 

Fig. 16 2D-cartoons of quasi-spherical nanoparticles protected with mesogenic or pro-mesogenic capping agents giving rise to liquid crystalline quasi-spherical nanoparticles. The three major approaches include the decoration with calamitic molecules in an end-on fashion (7), with dendrons featuring calamitic or polycatenar moieties at the termini (8), and with laterally substituted calamitic molecules in a side-on fashion (9). The concept shown for the quasi-spherical nanoparticle 7 was also successfully used for spindle-like nanoparticles [533, 534]... 

It is also of interest to consider the case of a microsphere at a non-electroactive substrate because it is used as a model for spherical nanoparticles (of radius rnp and area Anp) impacting on a surface [72, 73]. For this case the average stationary current is given by [74] ... 

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