Nanocomposites particle shape

Nanocomposite particles shape and dimension are observed using a scanning electron microscope and microanalyzed with an energy dispersive X-ray spectrometer (EDAX). The... 

M.A. Osman, A. AtaUah, High-density polyethylene microand nanocomposites effect of particle shape, size and surface treatment on polymer crystalltnity and gas permeability, Macromolecular Rapid Communications 25 (2004) 1540-1544. 

Sol-gel synthesis presents a soft route to materials preparation, where a sol is obtained from the hydrolysis and condensation of a precursor which can form a gel before subsequent drying and heat treatment allows for conversion to a desired phase. An example of a modified sol-gel approach is the preparation of an iron oxide-silica nanocomposite. Here, the iron alkoxide precursor [Fe(OBu )2(THF)]2 has been hydrolysed using millipore water under ultrasonic irradiation in the presence of tetraethylorthosilicate (TEOS) to afford a nanocomposite comprised of silica and y-Fe203 nanoparticles in a single step. The concentration of TEOS added also affects the particle shape, with roughly spherical particles formed with lower and nanorods at higher concentrations, respectively. 

First and paramount method of nanocomposites characterization is, undoubtedly, transmission dectron microscopy (TEM), which allows one to observe the particle shape, to determine particle sizes, to control the homogeneity of the composite and to obtain the histogram of nanoparticle sizes (Figs. 1, 2). TEM (especially axial bright fidd microscopy) is the most informative method of characterization with the resolution up to units of angstroms allowing visualization of the lattice plane and measurement of interplanar distances of nano-partides. However, its application to polymer composites is hindered due to charge instability of some polymers (such as PVA [39], or PVDF [35]) and by the difficulty of sample preparation. 

Kalfus J and Jancar J (2007) Elastic response of nanocomposite poly(vinylacetate)-hydroxyapatite with varying particle shape, Polym Comp 28 365-371. 

DPD simulation has been applied to predict the rheological and viscoelastic behaviors of nanopartide-polymer nanocomposites and to examine the effects of particle shape, particle-particle interaction, and partide dispersion states of such behaviors. It was found that partide-particle interaction has a distinct effect on the dynamic shear modulus. Havet and Isayev [39,40] proposed a rheological model to predict the dependence of dynamic properties of highly interactive filler-polymer mixtures on strain and the dependence of shear stress on shear rate. 

Osman M. A. and AtaUah A., High-density polyethylene micro- and nanocomposites effect of particle shape, size, and snrface treatment on polymer crystalhnity and gas permeability , Macromol Rapid Commun, 2004, 25, 1540-1544. 

However, for the dendrimer nanocomposite metallic systems this change in shape was not observed. Again, due to the high stability to intense laser pulses, the anisotropy value of the gold dendrimer nanocomposite, which can be viewed as a measure of the symmetry of the particle, did not change after several repeated cycles of measurements. It is possible that the initial optical pumping of the electron-phonon modes of the metal particles is partially absorbed by the encapsulating PAMAM dendrimer. 

The emission of the metal particles may thus originate from a band-to-band transition in the metal particle, which occurs at about 516 nm for gold [60, 119]. As stated above, the nature of the interaction of the dendrimer (PAMAM) host is still uncertain, there could be very strong electrostatic interactions that may play a part in the enhancement of the metal particles quantum efficiency for emission. However, one would expect that this enhancement would result in slightly distorted emission spectra, different from what was observed for the gold dendrimer nanocomposite. Further work is necessary to completely characterize the manner in which the dendrimer encapsulation enhances the emission of the metal nanoparticles. With further synthetic work in preparation of different size nanoparticles (in other words elongated and nonspherical shape particles, including nanorods) it may be possible to develop the accurate description of a... 

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