Nanometric particles

Adsorption of ions or molecules on metal clusters markedly affects their optical properties. It was shown that the intensity and the shape of the surface plasmon absorption band of silver nanometric particles, which is close to 380 nm, change upon adsorption of various substances [125]. The important damping of the band generally observed is assigned to the change of the electron density of the thin surface layer of the... 

Ouyang, M., Remy, J.S. and Szoka, F.C. (2000) Controlled template-assisted assembly of plasmid DNA into nanometric particles with high DNA concentration. Bioconjug. Chem., 11, 104-112. 

Dockery DW, Pope CA, Xu XP, Spengler JD, Ware JH, Fay ME, Ferris BG, Speizer FE (1993) An association between air pollution and mortality in 6 United States cities. N Engl J Med 329 1753-1759 Donaldson K, Li XY, MacNee W (1998) Ultrafine (nanometre) particle mediated lung injury. J Aerosol Sci 29 553-560... 

Tin(II) sulfide semiconductor nanometric particles have been prepared by the thermal decomposition at 350 °C in air of R4Sn4Se (R = Me, n-Bu and Ph). Further heating to 500 °C in an N2 atmosphere led to the pure orthorhombic Sn2S3. ... 

Because the size of lipoplex is a key factor in determining the tissue distribution as well as the cellular uptake, it would be a challenge to reduce the size of lipoplex to increase transfection efficiency. Recently, Dauty et al.43 succeeded in formulating plasmid DNA into stable nanometric particles with a diameter of less than 40 nm by synthesizing a dimerizable cationic detergent. 

Although particles are obtained by the RESS process recently nanometric particle production has been reported (32-39), in most cases micrometer- and submicrometer-sized (Table 1) (40-71). 

If reactive systems, as present in sol-gel type of coatings, are chosen for coating deposition using alkoxides or pre-hydrolysed systems, then control of the atmosphere is crucial as the atmosphere determines the evaporation rate of the solvent and the subsequent destabilisation of the sols. This leads to a gelation process and the formation of a transparent film due to the small (nanometre) particle size in the sols (Brinker, Hurd and Ward, 1988 Scriven, 1988 Brinker and Scherer, 1990). 

The synthesized materials posses large pore volume and a good thermal and hydrothermal stability. Table 1 shows textural properties of the calcined materials the use of a surfactant leads to higher surface areas and pore volume than those observed for reference C-0 and C-4 samples. On the other hand, the increase in surface area correlates well with the intensity of the carbonate bands observed by DRIFT. Examination of the N2-physisorption isotherms let us assume a non-ordered mesoporous structure. This was confirmed by the lack of a small angle X-ray difliraction peak. By XRD the Ce02 cerianite phase was identified and crystal size determined by the Rietveld method showed that samples C-1 through C-3 are nanometric particles with crystal size of about 4-7 nm while reference samples C-0 and C-4 were much larger (w30 and 19 nm, respectively). 

Nanometric particles of InP were readily prepared by the decomposition of an indium phosphide complex, In(PBu 2)3, at 167 °C in 4-ethylpyridine. The resulting material shows marked quantum confinement effects, and was investigated using optical absorption and photoluminescence spectroscopies, and TEM. " " Similar precursors were used... 

Blessing, T., Remy, J.-S., Behr, J.-P. (1998). Template oligomerization of DNA-bound cations produces calibrated nanometric particles, /. Am. Chem. Soc., 120 8519. 

This filler aggregation during the processing, observed with nanometric particles (carbon black) or micronic ones (metallic or carbon sphere), leads to a very difficult reproducibility of the material. Different approaches have been proposed to overcome these drawbacks. 

Ultrasonic and Microwave-assisted Synthesis of Nanometric Particles . The ob-... 

Recently, the so-called polyol process [210] has been used successfully to process magnetic nanoparticles with a very narrow particle size distribution [211,212]. This process is based on the reduction of metallic salt in solution, at a high temperature (100 ethylene glycol), resulting in nanometric particles. In this process, surfactants such as oleic acid are used to control particle growth and stabilize the nanoparticles. 

For industrial applications, metal catalysts should be repeatedly recycled or used in continuous mode for a long time. The introduction of gold catalysis in the aerobic oxidation of glucose has opened exciting perspectives Au is a biocompatible, nontoxic metal, which allows even superior productivities with respect to enzymatic catalysis [38], and no leaching problems have been observed using nanometric particles dispersed on different supports [43]. Compared with chemical oxidations, enzymatic catalysis suffers from more plant complexities... 

Fig. 13.4 Nanometric particles of different metals as catalysts for the aerobic oxidation of glucose. [Metal]=10 M, [Glucose]=0.4M, T=30°C, p02=l bar, pH=9.5.

Donaldson K, Li XY, MacNee W (1998) Ultrafine (nanometre) particle mediated lung injury. J Aerosol Sci 29 553-560... 

The recent interest in using stiff nanometric particles as reinforcement materials in polymeric matrixes, composites, or nanocomposites has been increasing. Two good examples of these types of particles are carbon nanotubes and cellulose nanofibers. Cellulose nanofibers, also reported in the literature as whiskers, nanocrystals, cellulose crystallites, or crystals, are the crystalline domains of ceUulosic fibers, isolated by means of acid hydrolysis, and are called in this way due to theb physical characteristics of stiffness, thickness, and length (Souza and Borsali 2004). 

Dispersions of nanometric particles are unusal because the potential barriers are low, since each particle carries a small number of effective charges. Moreover the range of repulsions is often rather short, because the dispersions have a very large surface area and this leads to high concentrations of ions in tiie aqueous medium. A consequence of these 2 features is that control of nanometric dispersions through electrostatic interactions is notoriously difficult. 

With nanometric particles the problem of polymer adsorption is different from the usual adsorption on macroscopic surfaces (Spalla O, Cabane B. Coll. Pol. ScL, in press). For one thing, nanometric dispersions have an extremely large surface area, hence they can adsorb a substantial amount of polymer before being saturated. In fact the amount of bound polymer is often comparable to the amount of particles in the system thus the system may be better described as a two-component system, similar in nature to mixed solutions of two polymers which interact with each other. This paper presents an analysis of such mixed particles+polymer dispersions from the point of view of two-component systems. 

Dispersion of nanometric particles and adsorbing polymers behave like reversible 2-component systems (A-B-solvent). Under conditions where attractions overcome repulsions there is a phase separation into a gel and a supernatant which have nearly the same polymer/particles ratio. Concentrate gels can be made easily through phase separation in the 2-phases region however 3iey are full of voids. These voids have been eliminated through compression and the equations of state of gels with different polymer/particles ratio have bwn determined. 

Microemulsion polymerisation is a new technique for the production of microlatexes made up of nanometric particles and polymers with specific properties. Let us summarise the main features of the process ... 

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