THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Multirate processing and spectrum analyzers

Experimental Techniques -     

Pseudo-non-contact AFM imaging?

Recent non-contact atomic force microscopy studies have demonstrated that imaging of single atom defects is possible. However, the imaging mechanism was unclear. Long-range forces of attraction, which are normally associated with non-contact mode, are not known to produce sufficient lateral resolution to image atoms. In this study, we suggest a mechanism that could be responsible for the resolution achieved. We use realistic interatomic interaction parameters to do numerical simulations. These simulations are in good agreement with experimental data. As a result, we are able to ‘separate' the attractive and repulsive forces acting between the AFM tip and the sample surface. Calculations indicate that the force responsible for image contrast in the experimental studies mentioned above, is in most cases the repulsive contact force, and not the long-range attractive force. We check our conclusions against a variety of interatomic interaction parameters and our results remain valid for any reasonable set of such parameters, including the power law of the attractive potential N<9.     

Regiospecific beta-functionalization of free-base porphyrins by pseudohalogens

Pseudohalogens based on iodine ('I-X') can be used to regiospecifically introduce chlorine atoms or acetoxy groups onto the beta-positions of meso-tetraphenylporphyrins (TPPs). TPPs and a quinoxaline derivative were reacted with iodine monochloride to give mono- or di-chlorinated porphyrins, such that when two chlorine atoms were added they were placed antipodally on the porphyrin ring. Reaction of the porphyrins with a mixture of iodine and silver acetate gave the corresponding mono- and di-acetoxylated porphyrins. The acetoxylated porphyrins could be simply transformed to the corresponding hydroxyporphyrins with subsequent oxidation with the Dess-Martin periodinane, giving a simple new route to chlorin-alpha-diones and bacteriochlorin-tetraones. From the products of the reactions and a UV-visible spectroscopic study, it is proposed that the reactions proceed via a single electron transfer mechanism through a porphyrin cation radical intermediate.     

Leaching behavior of nuclear waste glass heterogeneities

The results of a six-month burial experiment in granite are discussed. An alkali borosilicate simulated nuclear waste glass was buried in 3 m boreholes at the 345 m level in the Stripa mine. Some glass specimens containing crystallites exhibit preferential attack of the interface between crystalline and glassy phases. The crystalline phase, identified as spinel solid solution, exhibits better chemical resistance than the glassy phase. Results obtained from homogeneous and heterogeneous glasses (i.e., those containing a crystalline phase) are compared.     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Nonlinear compression of optical solitons

In this paper, we consider nonlinear Schrödinger (NLS) equations, both in the anomalous and normal dispersive regimes, which govern the propagation of a single field in a fiber medium with phase modulation and fibre gain (or loss). The integrability conditions are arrived from linear eigen value problem. The variable transformations which connect the integrable form of modified NLS equations are presented. We succeed in Hirota bilinearzing the equations and on solving, exact bright and dark soliton solutions are obtained. From the results, we show that the soliton is alive, i.e. pulse area can be conserved by the inclusion of gain (or loss) and phase modulation effects.