Colloids transmission electron microscopy

A new development is biphasic hydrogenation using solvent-stabilized colloid (SSCs) catalysts [39-41]. Palladium colloid systems, especially, were proven to give high reactivity and selectivity. Best solvents are dimethylformamide and particularly the two cyclic carbonic acid esters, ethylene carbonate and 1,2-propene carbonate. In these solvents sodium tetrachloropalladate - stabilized by a sodium carbonate buffer - is reduced with hydrogen to yield the solvent-stabilized palladium colloid. Transmission electron microscopy of the palladium colloid demonstrates that the colloid particles are spherical with an average diameter of 4 nm. 

Key words Cubatic Phase Plate-like colloids transmission electron microscopy... 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

In order to obtain Pt nanoparticles, aqueous solution of 10 M K2PtCl4, which contained 10 M (as monomer unit) of poly-NIPA or poly-NEA, was bubbled with Ar gas and then H2 gas. Then the reaction vessel was sealed tightly and kept in a water bath at a suitable temperature. At given reaction times, the vessels were opened and the samples for transmission electron microscopy (TEM) were prepared by soaking a grid (carbon substrate, Oken) in the colloidal solution and then drying it in the air. The TEM (Hitachi H-8100) was operated at 200 kV. 

Goldraich M, Talmon Y (2000) Direct-imaging cryo-transmission electron microscopy in the study of colloids and polymer solutions. In Alexandridis P, Lindman B (eds) Amphiphilic block copolymers self assembly and applications. Elsevier, Amsterdam... 

This section presents the result of the catalytic performances in the case of phenylacetylene hydrogenation reaction. The catalytic evaluation was performed in a classical well-stirred stainless steel reactor operating in batch mode under constant H2 pressure (10 bar) at 17°C using n-heptane as the solvent. As mentioned in Section 13.2.2, no modification of the particle size distribution has been observed by transmission electron microscopy before or after reduction of colloidal oxide particles. 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

Baalousha, M., Kammer, F. V. D., Motelica-Heino, M., Baborowski, M., Hofmeister, C., and Le Coustumer, P. (2006). Size-based speciation of natural colloidal particles by flow field flow fractionation, inductively coupled plasma-mass spectroscopy, and transmission electron microscopy/x-ray energy dispersive spectroscopy Colloids-trace element interaction. Environ. Sci. Technol. 40(7), 2156-2162. 

Wilkinson, K.J., Stoll, S. and Buffle, J. (1995) Characterization of NOM-colloid aggregates in surface waters coupling transmission electron microscopy staining techniques and mathematical modelling. Fresenius J. Anal. Chem., 351, 54—61. 

Moreover, the amphiphilic nonchiral polymer PG-0C(0)Ci5H3i was used by Mecking and coworkers in the preparation of nanometer-sized stable palladium colloids using PdCl2 or Pd(OAc)2. The formation of these palladium colloids was visualized by transmission electron microscopy and in the case of the amphiphilic polymer prepared from a PG scaffold of DPn = 63, a colloid of 5.2 1.8 nm average particle size was obtained. The... 

Figures 5 (a) and (b) show electron micrographs of the RuxSey particles in powder form, Fig. 5.5(a) and in colloidal form, Fig. 5.5(b). The generated particle size in both cases is ca.2 nm. It is, however, interesting that the colloidal route delivers particles with a narrow size distribution. After multiple analysis by EDX performed with transmission electron microscopy (TEM), and/or via Rut-herford backscattering spectroscopy (RBS) we concluded that the stoichiometry of the RuxSey compound corresponds to x 2 and y 1. This is another experimental evidence that the "real" chemical precursor is the intermediate...

Fig. 5.5. Transmission electron microscopy picture of RuxSey cluster-like materials, (a) in form of powder (b) from a colloidal solution (xylene).

Due to the high water solubility of MAA, partitioning of the MAA in the water phase was expected. After polymerization, the obtained miniemulsions (latexes) and the colloidal nanoMIPs were characterized by gravimetric analysis, dynamic light scattering (DLS), gas adsorption measurements (BET), and transmission electron microscopy (TEM) as shown in Fig. 9. 

In recent years a variety of spectroscopic and other techniques have been employed to investigate and monitor hydrosilylation reactions. The techniques include multinuclear NMR, transmission electron microscopy, extended X-ray absorption fine structure (EXAFS), etc. Results from these experiments indicate that depending on the precatalyst, colloids and/or mononuclear complexes take part as catalytic intermediates. 

---