Polymer-clay nanocomposites: chemical grafting of polystyrene onto Cloisite 20A

An account of the experiments on preparing polystyrene(PS) nanocomposites through grafting the polymer onto organophilic montmorillonite is reported.Cloisite 20A was reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety.Because the reaction may liberate HC1,it was performed in the presence of sodium hydrogencarbonate to prevent the exchange of quaternary alkylammonium cations with H~+ ions.Only the silanol groups on the edge of the clay react with vinyltrichlorosilane.The radical polymerization of the product with styrene as a vinyl monomer leads to chemical grafting of PS onto the montmorillonite surface.The homopolymer formed during polymerization was separated from the grafted organoclay by Soxhlet extraction.Chemical grafting of the polymer onto Cloisite 20A was confirmed by infrared spectroscopy.The prepared nanocomposite materials and the grafted nano-particles were studied by XRD.Exfoliated nanocomposites may be obtained for 0.5 wt%-l wt%clay content.The nanocomposites were studied by thermogravimertic analysis(TGA) dynamic thermal analysis(DTA) and dynamic mechanical analysis (DMTA).     

H-point standard addition method--first derivative spectrophotometry for simultaneous determination of palladium and cobalt

H-point standard addition method (HPSAM) has been applied for simultaneous determination of palladium and cobalt in trace levels, using disodium 1-nitroso-2-naphthol-3, 6-disulphonate (nitroso-R salt) as a selective chromogenic reagent. Palladium and cobalt in the neutral pHs form red color complexes with nitroso-R in aqueous solutions and making spectrophotometric monitoring possible. Simultaneous determination of palladium and cobalt were performed by HPSAM--first derivative spectrophotometry. First derivative signals at the two pairs of wavelengths, 523 and 589 nm or 513 and 554 nm were monitored with the addition of standard solutions of palladium or cobalt, respectively. The method is able to accurately determine palladium/cobalt ratio 1:10 to 15:1 (wt/wt). Accuracy and reproducibility of the determination method on the various amounts of palladium and cobalt known were evaluated in their binary mixtures. To investigate selectivity of the method and to ensure that no serious interferences were observed the effects of diverse ions on the determination of palladium and cobalt were also studied. The recommended procedure was successfully applied to real and synthetic cobalt or palladium alloys, B-complex ampoules, a palladium-charcoal mixture and real water matrices.     

Theoretical and computational investigations on thermodynamic properties, effective site diameters, and molecular free volume of carbon disulfide fluid

A newly proposed theory [R. Laghaei et al., J. Chem. Phys. 124, 154502 (2006)] was extended to polyatomics and applied to compute the density and temperature dependence of the effective site diameters of carbon disulfide fluids. The generic van der Waals (GvdW) theory was also extended to polyatomics in order to calculate the GvdW parameters and the molecular free volume using the effective site diameters as the repulsion-attraction separation distance. A three-site Lennard-Jones potential available in the literature was slightly modified and used in Monte Carlo simulations to obtain the functions appearing in the effective site diameter and GvdW expressions. The interaction potential was examined to reproduce the fluid phase thermodynamic properties using Gibbs ensemble Monte Carlo simulations and also the equation of state in the liquid phase using NVT Monte Carlo (NVT-MC) simulations. Comparison between the simulation results and experimental data shows excellent agreement for the densities of the coexisting phases, the vapor pressure, properties of the predicted critical point, and the equation of state. NVT-MC simulations were performed over a wide range of densities and temperatures in sub- and supercritical regions to compute the effective site diameters, the GvdW parameters, and the molecular free volume. The molecular structure in terms of the site-site pair correlation functions, the density dependence of the effective site diameters, and the density and temperature dependence of the GvdW parameters and molecular free volume were studied and discussed. The GvdW parameters were fitted to empirical expressions as a function of density and temperature. The computed molecular free volume will be used in future investigations to study the transport properties of carbon disulfide.