Particle composition shape

DNA is used as a stabilizer/template in the formation of CdS nanoparticles and its mesoscopic aggregates. Use of linear duplexes of DNA in solution help in this formation. In the beginning it was inferred that in DNA CdS nanoparticles split to form Cd and S . The role of DNA-nanoparticle interaction was unclear. When studied further it was realized that the DNA base sequence had a significant effect on the size of the CdS particles and their photophysical properties. DNA sequence in general and base adenine in particular had its influence on CdS particles. Coffer and co-workers 1996 developed a technique to synthesize well-defined mesoscale stractures in solution by binding a template DNA strand to a solid substrate. By controlling the particle composition, shape, length, and sequence of the DNA template via this approach a number of mesoscale structures were obtained. 

MMT nanoparticles are well known to be a mixture of several natural compounds with nonuniform composition and particle size [27]. For example, MMT minerals from different deposits might differ considerably in composition. This variation in composition of MMT significantly complicates the task of making functional nanocomposites with prescribed properties for targeted applications. Therefore, there is a need to develop synthetic nanofillers with prescribed particle composition, shape, and size for use as fillers in polymer nanocomposites with well-defined properties. In this area, synthetic nanodimensional silicates may provide a number of opportunities in polymer nanocomposites that is relatively little studied and poorly understood relative to the well-studied polymer nanocomposites filled with natural layered MMTs [28-32]. In contrast to the commonly used layered MMT compounds, it is envisaged that use of nanoparticles with different morphology (e.g.,... 

Source sampling of particulates requites isokinetic removal of a composite sample from the stack or vent effluent to determine representative emission rates. Samples are coUected either extractively or using an in-stack filter EPA Method 5 is representative of extractive sampling, EPA Method 17 of in-stack filtration. Other means of source sampling have been used, but they have been largely supplanted by EPA methods. Continuous in-stack monitors of opacity utilize attenuation of radiation across the effluent. Opacity measurements are affected by the particle size, shape, size distribution, refractive index, and the wavelength of the radiation (25,26). 

Particles can be characterized by their composition and crystallographic phase, as well as by their size, density, and shape. The particle composition can have a dramatic impact on the amount of incorporation obtained for a particular bath composition. For instance three times more TiC>2 than AI2O3 has reportedly [54] been incorporated into a Ni matrix, under the same deposition conditions. 

Fig. 1.1.13 Concentration domains of solutions containing FeClj and HCI aged at 100°C for 24 h (upper) and for 1 week (lower). N, no particle formation. Particle shapes D. double ellipsoids E, ellipsoidal 1, irregular of varying sizes R. rod-like S, spherical. Pairing of symbols indicates a mixture of corresponding particles in the suspension. Particle composition R, p-FeOOH all other particles, a-Fe2Oi. (From Ref. 65.)...

The compositions, shapes, sizes, appearance, and range of particle types should all be considered during interpretation. Particles that are individually consistent with FDR should not be found with otherwise similar particles that are in some way inconsistent with FDR.170... 

The nascent HDL particles change shape and composition as they acquire additional free cholesterol by passive cellular diffusion of free cholesterol from cell membranes or from other plasma lipoproteins. HDL surface-localized LCAT progressively converts the free cholesterol on the surface of the particles to cholesterol ester, which occupies the core of the lipoprotein particle. This process converts the shape of the HDL particles from discoidal to spherical. The lipid unloading of HDL in the liver follows at least two pathways. In the first route, the cholesterol ester transfer protein (CETP) mediates cholesterol ester transfer from HDL to VLDL and LDL in exchange for triglyceride LDL in turn are taken up by the liver via the LDL receptor. In the second route, HDL binds to the scavenger receptor Bl, and cholesterol esters are selectively taken into the liver cells without internalization of HDL proteins (Fig. 15-2). 

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). 

The particle properties are the least controllable process parameters. The choice of particle material is limited by the desired composite properties. The chosen particle material and (commercial) availability again restrict particle shape and size. Consequently the particle properties set the limits for the attainable particle composite contents. 

Equations (16) and (18) discriminate between intraparticle and interparticle interference effects embodied in bj(q. t) and exp rq- ry(/)—r/(/) ), respectively. The amplitude function bj(q.t) contains information on the internal structure, shape, orientation, and composition of individual particles. Variations of bj(q.t) across the particle population reflect the polydispersity of particle size, shape, orientation, and composition. The phase function expjrq (ry (r) — r/(/)]( carries information on the random motion of individual particles, the collective motion of many particles, and the equilibrium arrangement of particles in the suspension medium. 

The development of synthetic methods is one of the fundamental aspects to the understanding and development of nano-scale materials. The novel properties and numerous applications of nano-scale materials have encouraged many researchers to invent and explore preparation methods that allow control over such parameters as particle size, shape, size distributions and composition. While considerable progress has taken place, one of the major challenges is the development of a synthetic toolbox which would afford access to size and shape control of structures on the nano-scale and conversely allow scientists to study the effects these parameters impart to the chemical and physical properties of the nanoparticles. 

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