Composite colloids of gold and polypyrrole were prepared using two different methods: 1, using pyrrole colloid, created by the oxidation of pyrrole by ferric chloride, to subsequently reduce chlorauric acid and, 2, oxidizing pyrrole monomer with chlorauric acid in a sodium dodecylbenzene sulfonate solution. In each case, the polypyrrole colloid consisted of irregularly shaped particles approximately 500 nm in diameter. The gold produced in each case was in the form of irregular spheres, approximately 407 nm in diameter in method 1 and 13 nm in method 2. X-ray photoelectron spectroscopy was used to determine the oxidation state of the species present. Transmission electron microscopy and light scattering data were used to determine the particle sizes of both gold and polypyrrole colloids. Energy dispersed spectrum X-ray analysis and electron diffraction were used to confirm the presence of metallic gold in the composite colloids. The second-order rate constant for the reaction of chlorauric acid with pyrrole in dilute solution was found to be 13 M Ϫ1 s Ϫ1 . Aqueous solutions of palladium, platinum, rhodium, cobalt, tin, silver, zinc, nickel, titanium, cadmium, mercury, arsenic, and selenium were also examined for their potential to act as oxidants to produce composite polypyrrole colloids. Palladium, platinum, and rhodium salts were suitable oxidants, producing polypyrrole in less than 12 h.Methods for the preparation of colloidal gold have been known for hundreds of years. 1 Over this time, colloidal metals have found applications in biochemistry, 2 cytology, 3 microscopy, 4 and catalysis 5 as described in recent reviews. Most of the procedures used to prepare colloidal metals rely on micelles as a stabilizer containing either metal salts or a reductant, thereby acting as microreactors to control the size distribution of the metal particles produced. The various morphologies that can be produced by this method have been described as ''cherries'' ͑one central metal particle͒, ''raspberries'' ͑multiple internal particles͒, ''strawberries'' ͑a layer of metal particles outside the micelle boundary͒, and ''red currant'' or ''ginger root'' ͑a dendritic type with strings of metal particles radiating away from the central micelle͒. 6 Under conditions in which the reductant is a monomer that undergoes oxidative polymerization, a polymer/metal composite colloid can be formed. These are unique materials, with interesting electronic, 7 magnetic, 8,9 optical, 10 and nonlinear optical properties, 11 depending on the metal and polymer employed. The metal thus supported can also be catalytically 6,12,13 or electrochemically 14-16 useful, especially with a conducting polymer as part of the system. Especially in terms of catalysis, polymer-supported precious metals have many applications. For example, polymer-supported platinum and rhodium catalysts have been used to carry out hydrogenation reactions. 12 The polymer allows the control of the environment around the metal center, thus influencing selectivity of the hydrogenation rea...

The adsorption of methanol-D2O and acetonitrile-D2O solutions at model chromatographic interfaces (octadecylsiloxane and quartz) was studied using sum-frequency spectroscopy. Methanol did not adsorb at either interface in detectable quantities, while acetonitrile adsorbs at the octadecylsiloxane- and quartz-solution interfaces in a concentration-dependent manner and is well ordered at the interface. Adsorption of acetonitrile was decreased by the addition of KCl at 10 and 100 mM. Acetonitrile adsorption was also observed during simulated gradient elution, demonstrating that adsorption of acetonitrile occurs on a time scale relevant to actual chromatographic separations. Examination of the OH stretch spectra of acetonitrile-H2O and methanol-H2O solutions at the interface revealed concentration-dependent changes in the acetonitrile-H2O spectra that are consistent with hydrogen bonding between interfacial water and acetonitrile, indicating that interfacial water is involved in mediating acetonitrile adsorption. The OH stretch spectra of methanol-H2O solutions showed no such changes.

No abstract

Model reversed-phase chromatographic interfacial systems were examined using sum-frequency generation (SFG) spectroscopy to study the effect of solvent on the structure and conformation of the stationary phase. Monolayers formed from mixed C 18 and C 1 alkysilanes (both polymeric octadecyltrichlorosilane-methyl trichlorosilane mixed monolayers and monomeric octadecyldimethylchlorosilane-trimethylchlorosilane mixed monolayers) on fused silica were examined in contact with air, deuterated acetonitrile (CD 3 CN), D 2 O, and mixtures of CD 3 CN and D 2 O. When mixed composition (C 18 and C 1 ) monolayers were examined, significant disorder was observed in the alkyl chains for all solvents examined at intermediate alkyl chain densities for the polymeric materials, and at all chain densities for the monomeric materials. Maximum order for intermediate polymeric chain densities was found to occur in contact with 40-50 vol % D 2 O solutions. These results indicate that solvent microheterogeneity has a large effect on alkyl chain order.

Competitive adsorption of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (TMDD) with octanesulfonic acid Na+ salt, decanesulfonic acid Na+ salt, dodecanesulfonic acid Na+ salt, and protonated and deprotonated octanoic acid was observed using sum frequency generation (SFG) spectroscopy. SFG spectroscopy allows the direct observation of the relative surface density of TMDD. Various models of competitive adsorption for mixed surfactant systems were compared. Models taking into account kinetic, steric, and electrostatic factors were compared to the experimental data. For systems not undergoing a two-dimensional phase transition, a model incorporating steric and kinetic factors provided the best agreement with experimental observations.

No abstract

The keto-enol equilibria of the beta-diketones acetylacetone, trifluoroacetylacetone, and hexafluoroacetylacetone were determined using Fourier transform infrared spectroscopy in a novel high-pressure capillary cell. Acetylacetone and its fluorinated analogues were studied as neat liquid and as supercritical CO2 solutions at pressures up to 3.1 kbar. The keto form was found to be favored at high pressure and low temperature. The change in partial molar volume and enthalpy between the keto and enol forms was determined for the acetylacetone and trifluoroacetylacetone. Under all conditions studied, only the enol form of hexafluoroacetylacetone was observed. Based on the thermodynamic data obtained, there appears to be no advantage gained in conducting metal extractions at high pressures and low temperatures using acetylacetone or trifluoroacetylacetone.

Sputter depth profiling is commonly used to obtain valuable information regarding the three dimensional distribution of elements within a sample, and is one of the best ways to measure the composition of a buried interface or the uniformity of a thin film. X-ray photoelectron spectroscopy (XPS) is one of the analysis tools often used in conjunction with ion beam erosion to obtain sputter depth profiles. However, to obtain accurate depth information it is often necessary to understand better the sputtering process for a specific materials system. Artifacts such as differential sputtering, varying sputter rates and ion beam-induced chemistry are well known. Here, however, we present evidence from experiments on a porous thin film deposited on an Si wafer that relatively small chemical and/or structural changes in a nanoporous film can affect the rate of erosion measured during sputter depth profiling. Reproducible variations in sputter rate are found with chemical modification leading to compositional changes of the nanoporous thin film. The origin of the sputter rate changes is discussed with the aid of results obtained using Fourier transform infrared spectroscopy, profilometry, nuclear reaction analysis, electron microscopy and XPS-based depth profiling.