Nanocrystalline domain identification in gold films, by backscattered electron imaging and energy-filtered transmission electron microscopy

Gold nanocrystallites dispersed in an inhomogeneous gold matrix are detected by high-resolution scanning electron microscopy using a field emission source and backscattered electron detection in the composition mode, as well as by energy-filtered transmission electron microscopy in the plasmon energy region. The identity of the nanocrystalline domains was established by observing the same evaporated gold film samples but using bright-field, dark-field, electron diffractogram, and electron energy loss spectroscopy images in the transmission electron microscope. Comparison of these images shows that backscattered electron and plasmon energy detection can be used to identify crystalline domains in an otherwise chemically uniform sample. (C) 2001 Academic Press.23514

The effect of the solvent on the morphology of cellulose acetate/montmorillonite nanocomposites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Nanocomposites of cellulose acetate and sodium montmorillonite were prepared using the solution intercalation method with different solvents. The effects of solvent type on the morphology, thermal and mechanical properties of the nanocomposites were investigated by X-ray microtomography and diffraction, field emission scanning electron microscopy, analytical transmission electron microscopy based on electron loss spectroscopy imaging and dynamical mechanical analysis. XRD and TEM results indicated that the dispersion and delamination of the clay are achieved when the solvent presents favorable interactions with the clay. In this case, the storage modulus and the glass transition temperature are significantly higher than those of pure cellulose acetate. The results show that the solvent has a major effect in controlling the morphology of cellulose acetate and cellulose acetate nanocomposite and could be used as a process parameter to produce films with a range of properties. (C) 2008 Elsevier Ltd. All rights reserved.501161170Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Latex macrocrystal self-assembly dependence on particle chemical heterogeneity

A self-arrayed poly(styrene-co-hydroxyethylmethacrylate) film surface was examined using microscope techniques possessing microchemical capabilities, together with standard (control) techniques. Secondary electron (SEI) and backscattered electron (BEI) images obtained in a field-emission scanning microscope, as well as scanning atomic force (AFM) and electric potential (SEPM) images, show an accumulation of hydrophobic particles around point and line macrocrystal defects. Defects in self-arrayed latex films are thus largely due to latex particle chemical heterogeneities. This result is consistent with the capillary adhesion-dependent models for macrocrystal formation and it shows the importance of latex purification, prior to macrocrystallization. (C) 2001 Elsevier Science B.V. All rights reserved.18141699495

Hydrophobic polymer modification with ionic reagents: Polystyrene staining with water-soluble dyes

Homopolymer polystyrene films tinted with methylene blue and other hydrophilic cationic dyes are made following anew two-step procedure: dye adsorption in latex particles, followed by polymer plasticization with a suitable solvent. The dyed polymer is soluble in nonpolar solvents, and the dyes do not phase separate, even in nonsolvents for the pure dye salts. Microanalytical data on the particles and films were acquired using energy-loss spectroscopy imaging (ESI-TEM) and scanning electric potential microscopy (SEPM). The results are interpreted considering that (i) the polystyrene latex particles have a mild ionomer character, due to the charged sulfate groups arising from the polymerization initiator and bound to the chain ends; (ii) there is formation of ion pairs made out of dye cation and chain-end sulfate; (iii) the cationic dye self-associates, as evidenced by a pronounced metachromatic behavior. A nonpolar polymer can thus be made compatible with a basic dye without any special chain modification, just by using this new procedure based on dye sorption followed by diffusion.19187580758

Controlled nanoparticle assembly by dewetting of charged polymer solutions

In this paper, we present an alternative approach for controlled nanoparticle organization on a solid substrate by applying dewetting patterns of charged polymer solutions as a templating system. Thin films of charged polymer solutions dewet a solid substrate to form complex dewetting patterns that depend on the polymer charge density. These patterns, ranging from polygonal networks to elongated structures that are stabilized by viscous forces during dewetting, serve as potential templates for two-dimensional nanoparticle organization on a solid substrate. Thus, while nanoparticles dried in pure water undergo self-assembly to form close-packed arrays, addition of charged polymer in the dispersion leads to the formation of open structures that are directed by the dewetting patterns of the polymer solution. In this study, we focus on the application of elongated structures resulting from dewetting of high-charge-density polymer solutions to align nanoparticles of silica and gold into long chains that are several micrometers in length. The particle ordering process is a two-step mechanism: an initial confinement of the nanoparticles in the dewetting structures and self-assembly of the particles within these structures upon further drying by lateral capillary attractions.20114430443

Preparation of natural rubber-montmorillonite nanocomposite in aqueous medium: evidence for polymer-platelet adhesion

Nanocomposites of natural rubber latex and layered silicates are prepared by a mild dispersion shear blending process. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that clay particles are well dispersed in the dry latex and the platelets have a preferential orientation, forming translucent nanocomposites. These show tensile mechanical properties analogous to those obtained with vulcanized rubber as well as an increased solvent resistance, which is expected considering that there is significant adhesion between clay lamellae and rubber. Nanocomposite swelling is strongly anisotropic. Natural rubber properties may thus be strongly modified by nanocomposite formation producing unprecedented combinations of properties. (c) 2005 Elsevier Ltd. All rights reserved.47267267

Elemental mapping in natural rubber latex films by electron energy loss spectroscopy associated with transmission. electron microscopy

Element distribution maps from Hevea brasiliensis natural rubber latex thin films were obtained, by electron energy-loss spectroscopic imaging in a low-energy (80 kV) transmission electron microscope. C, N, O, P, Na, Ca, Mg, Al, Si, and S maps are presented for latex fractionated by centrifugation, either followed by dialysis or not. Most elements forming non-carbon compounds are concentrated in small, electron-dense spots surrounded by a carbon-rich matrix of polymer, thus showing that the rubber is filled with small particles compatible with the polyisoprene matrix. Ca distribution is unique, since it closely parallels the C distribution, evidencing an important role for -COO--Ca2+-COO- ionic bridges in the structure of natural rubber.74112541254

ESI-TEM Imaging of surfactants and ions sorbed in Stober silica nanoparticles

The sorption of surfactants and NaCl in silica nanosized particles creates unexpected spatial distributions of solutes that were evidenced by electron spectroscopy imaging in the transmission electron microscope (ESI/TEM). The spectral images show that simple ions (Na(+), Cl(-), Br(-)) are actually absorbed within the particles irrespective of their charges, while surfactant chains are adsorbed at the particle surfaces. The expected effect of the surfactants on particle aggregation is also observed in the micrographs. In the case of salt, close-packed silica particle arrays are formed at low ionic strength, but only coarse aggregates form at higher salt concentrations. The particles absorb both Na(+) and Cl(-) ions in similar amounts, from 0.5 mol L(-1) NaCl, but Na(+) ions are depleted from the particles' immediate outer vicinity, where Cl(-) ions are in turn accumulated. These results confirm that Stober silica nanoparticles are highly porous and reveal their potential usefulness as carriers of small molecules and ions, due to the small particle size, exceptional colloidal stability, and this newly found sorption behavior.22177159716