Dispersed nanoparticles

Oluwafemi, O. S. and Revaprasadu, N. (2009). A Facile, Green" One - Step, Room Temperature Synthesis of a Series of monodispersed MSe(M = Cd or Zn)Water Dispersible Nanoparticles. Mater. Res. Soc. Symp. Proc., 1138, FF 12-19. 

Yu, K.M.K., Steele, A.M., Zhu, J Fu, Q.J. and Tsang, S.C. (2003) Synthesis of well-dispersed nanoparticles within porous solid structures using surface-tethered surfactants in supercritical CO2-Journal of Materials Chemistry, 13 (1), 130-134. 

Developments in modern CVD allow to improve the deposition of thin films and bulky coatings nevertheless, an additional major issue remains the building of nanostructured materials such as ultra-thin films or dispersed nanoparticles. For these applications, the control of the deposit at the atomic or nano-scale level is essential. Consequently, the role of surface chemistry occurring between the CVD precursor and the substrate, as well as the gas-phase main physical properties have to be indisputably clarified. 

From our research group Santra et al. [11,41,42] reported the development of novel luminescent nanoparticles composed of inorganic luminescent dye RuBpy, doped inside a sihca network. These dye-doped silica nanoparticles were synthesized using a w/o microemulsion of Tx-lOO/cyclohexane/ n-hexanol/water in which controlled hydrolysis of the TEOS leads to the formation of mono dispersed nanoparticles ranging from 5-400 nm. This research illustrates the efficiency of the microemulsion technique for the synthesis of uniform nanoparticles. These nanoparticles are suitable for biomarker application since they are much smaller than the cellular dimension and they are highly photostable in comparison to most commonly used organic dyes. It was shown that maximum liuninescence intensity was achieved when the dye content was around 20%. Moreover, for demonstration... 

Some important observations, which should apply de facto to many nematic systems containing dispersed nanoparticles, particularly those with metal or semiconductor cores, were reported in 2006 by Prasad et al. [297]. The authors found that gold nanoparticles stabilized with dodecanethiol decreased the isotropic to nematic phase transition of 4-pentyl-4 -cyanobiphenyl (5CB) almost linearly with increasing nanoparticle concentration (x p) and increased the overall conductivity of these mixtures by about two orders of magnitude. However, the anisotropy of the electric conductivity (Act = [Pg.349]

Fig. 15.8. Distribution of charged particles in dense single-layer coating composed of mono-disperse nanoparticles (numerical simulation for dielectric constants e = 1 and e = 10, T = 100°C). Z is the charge multiplicity of nanoparticles.

Figure 3.30 Synthesis route of PMO magnetic hollow spheres (a) hydrophobic, stearic acid-capped Fes04 nanoparticles in an organic phase are treated with CTAB to produce (b) water-dispersible nanoparticles, (c) Formation of FC4 vesicles leads to encapsulation of the CTAB-stabilized Fe304 nanoparticles, (d) Addition of BTME/CTAB forms the outer ethane-bridged PMO shell surrounding the vesicles. (See color insert.)...

Several length-scales have to be considered in a number of applications. For example, in a typical monolith reactor used as automobile exhaust catalytic converter the reactor length and diameter are on the order of decimeters, the monolith channel dimension is on the order of 1 mm, the thickness of the catalytic washcoat layer is on the order of tens of micrometers, the dimension of the pores in the washcoat is on the order of 1 pm, the diameter of active noble metal catalyst particles can be on the order of nanometers, and the reacting molecules are on the order of angstroms cf. Fig. 1. The modeling of such reactors is a typical multiscale problem (Hoebink and Marin, 1998). Electron microscopy accompanied by other techniques can provide information on particle size, shape, and chemical composition. Local composition and particle size of dispersed nanoparticles in the porous structure of the catalyst affect catalytic activity and selectivity (Bell, 2003). 

Use of high-k nanoparticles in polymer dispersions — To solve the void and cracking issue, it is possible to disperse nanoparticles in a polymer matrix. The drawback is that this typically limits the actual dielectric constant boost to fractional amounts, since it is difficult to achieve significant mass loading of the nanoparticles within the polymer, resulting in a final film with only a small fraction of nanoparticle additive. 

Figure 10.21 Schematic illustration of solution impregnation used to synthesize highly dispersed nanoparticles on a porous support.

CH4 oxidation has been experienced for ceria supported on a barium hexaaluminate, an heat resistant support. Preparation by a new reverse microemulsion method leads to ceria nanoparticles deposited on support and having a BET area close to 100 mVg after calcination at 1000 0 [72]. Such ultrahigh disperse nanoparticles show exceptional thermal resistance the authors mentioned that ceria particles prepared with a size of 6 nm sinters only to 18 nm after a calcination at 1IOO°C under a water containing atmosphere. Of course excellent activity in methane combustion has been observed. According to their experimental conditions calculated specific activity expressed as mol(CH4).h. m was estimated to 6.4x10 at 500°C whereas Bozo [44J reported a value of 1.5x1 O at the same temperature both values look similar. Thus the difference in methane conversion may be related to BET area only which is spectacularly preserved using the reverse micro-emulsion method for synthesis. 

The heart of a fuel cell is the membrane electrode assembly (MEA). In the simplest form, the electrode component of the MEA would consist of a thin film containing a highly dispersed nanoparticle platinum catalyst. This catalyst layer is in good contact with the ionomeric membrane, which serves as the reactant gas separator and electrolyte in this cell. The membrane is about 25-100 p,m thick. The MEA then consists of an ionomeric membrane with thin catalyst layers bonded on each side. Porous and electrically conducting carbon paper/cloth current collectors act as gas distributors (Figure 27.1). Since ohmic losses occur within the ionomeric membrane, it is important to maximize the proton conductivity of the membrane, without sacrificing the mechanical and chemical stability. 

Promotion and metal-support interactions play a key role in the design of successful commercial finely dispersed nanoparticle catalysts [1-5]. The detailed molecular mechanism of promotion [6] and particularly of metal-support interactions [7,8] is still a subject of intensive study and dispute. 

RESS Rapid expansion of supercritical solutions through a nozzle causing rapid nucleation of product into highly dispersed nanoparticles... 

The applicability of this technique is limited to metal hydroxides or carbonates that can be co-precipitated with Au(OH)g. Gold can be supported in the form of well-dispersed nanoparticles, by CP, on a-Fe203, C03O4, NiO and ZnO, but not on Ti02, Cr203, MnO, and CdO [28]. 

Although, the reasons for the catal3dic activity of gold are not as yet fully understood, the presence of gold as well-dispersed nanoparticles (<10nm)... 

Different experimental approaches for the application of NMR spectroscopy to dispersed nanoparticles are summarized and briefly discussed regarding their specific advantages and disadvantages. A general numeric approach for the analysis of the obtained data is introduced which accounts for rotational and lateral diffusion of the particles in a fluid medium. The applicability of the NMR experiments together with the numerical analysis of the resulting spectra is demonstrated on various examples which cover the particle structure, phase transitions, decomposition pathways, molecular exchange at phase boundaries, and release processes. 

---