Reaction kinetics of organo-clay hybrid films: In-situ IRRAS, FIM and AFM studies

In this paper we report the reaction kinetics of nanodimensional clay saponite and hectorite with an amphiphilic cation octadecyl rhodamine B (RhB) in hybrid Langmuir monolayer at the air-aqueous clay dispersion interface. The surface pressure-molecular area (π-A) isotherms were strongly influenced by the presence of clay and the lift-off area of the cationic amphiphile shifted to progressively larger area. In-situ fluorescence imaging microscopic (FIM) studies showed the formation of micro-order domains in the organo-clay hybrid monolayer films at the air-clay dispersion interface. In-situ infrared reflection-absorption spectroscopy (IRRAS) was used to demonstrate the reaction kinetics. The time taken to complete the reaction kinetics for RhB-hectorite hybrid films is larger than for RhB-saponite hybrid films. Atomic force microscopic images of hybrid Langmuir-Blodgett films gave compelling visual evidence of the incorporation of clay platelets into the hybrid films, whose density increased with the progress of reaction kinetics.     

Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Reactions at the liquid silicon/silica glass interface

Experiments have been carried out to determine the nature and origin of the spots growing on silica glass surfaces in contact with liquid silicon during CZ–Si crystal growth. Silica glass ampoules were filled with silicon and tempered between 5 min and 40 h at a temperature (1693 K) slightly above the melting point of silicon. Cross sections of the ampoules with solidified silicon have been examined by scanning electron microscopy and optical polarization microscopy. In addition cross sections from commercial silica glass crucibles used in the Czochralski process or dipped into the silicon melt were investigated with the same methods. At the silicon/silica glass interface different reaction zone morphologies were detected. A solution-precipitation mechanism is suggested for the fast lateral growth of the reaction zone, which is proposed to consist of small cristobalite crystals embedded in a silica glass matrix.     

Macroscopic,Hierarchical, Two-Dimensional Self-Assembly

By tailoring capillary interactions at a fluid–fluid interface, a hierarchical two-dimensional self-assembly of hexagonal millimeter-sized poly(dimethylsiloxane) plates has been demonstrated (see picture). The strength and direction of capillary forces between plates was controlled by patterning of the surfaces of the plates to be hydophobic or hydrophilic. The thick lines indicate hydrophobic faces whose mutual attraction forms the basis of capillarity.     

玻璃微、纳米管及其在电分析化学中的应用

本文简单介绍了玻璃微、纳米管的发展历史及其制备进展。对其在分析化学中的应用进展,特别对其在液/液界面电化学和电分析化学研究中的应用进行了较详尽地评述和展望。     

Acoustic waves in (0 0 1) anisotropic polytype heterostructures

We have studied the acoustic waves of (0 0 1) polytype heterostructures formed by slabs of cubic crystals. We have considered symmetric and asymmetric heterostructures formed by AlN, GaN and InN in the zinc-blende structure due to the potential applications of these materials. The anisotropy of the materials has been taken into account and the different propagation directions ranging from the [1 0 0] to the [1 1 0] have been considered. We obtain the dispersion relations for different propagation directions. The coupling between the spatial components of the elastic displacements is different for symmetry and general propagation directions. The spatial localization of the modes in the heterostructures has also been obtained.     

CdTe and PbTe nanostructures on the oxidized pentagonal surface of an icosahedral AlPdMn quasicrystal

By means of congruent evaporation, we have deposited CdTe and PbTe onto the oxidized fivefold-symmetry surface of an icosahedral AlPdMn quasicrystal. This procedure results in the formation of nanocrystals in both cases. While the azimuthal orientations of the crystallites are random, the polar orientations are well defined. The crystalline CdTe and PbTe domains expose their (1 1 1) and (0 0 1) faces, respectively, which are aligned parallel to the pentagonal surface of the quasicrystal. The nanometric size of the domains is not a result of the lattice mismatch between the growing film and the substrate as usually observed in molecular-beam epitaxy, but of the limited size of the oxide domains of the substrate surface.     

Numerical simulation of the horizontal Bridgman growth. Part III: Calculation of the interface

We study the transient motion of the solidification front during the growth of semiconductor crystals in the horizontal Bridgman geometry. The calculation is based on a two-dimensional flow. We use finite elements which deform with the motion of the interface. The energy equation is coupled with the isothermal constraint of the interface in an implicit transient algorithm. Several examples show the oscillatory motion of the interface caused by the periodic flow of the melt, and they reveal the importance of the growth rate on the shape of the interface.     

On-line coupling of supercritical CO2 extraction with reversed-phase liquid chromatography for the quantitative analysis of analytes in aqueous matrices

The first report of on-line coupled supercritical fluid extraction (SFE) with reversed-phase liquid chromatography for the quantitative analysis of analytes in aqueous matrices is described. Two commercial systems (e.g. SFE and HPLC) were connected via a single six-port injection valve. By using water to eliminate residual decompressed CO2 gas in the solid-phase extraction trap, quantitative extraction and transfer were achieved for the target analytes (progesterone, phenanthrene, and pyrene) spiked in water, as well as in real samples (urine and environmental water). During each extraction, no restrictor plugging was realized. Extraction temperature and pressure were optimized. Different amounts of salt were added to the aqueous matrix to enhance ionic strength and thus extraction efficiency. Methanol and 2-propanol were used as CO2 modifiers. Compared with dynamically mixing modifier with the CO2 extraction fluid, pre-spiking the same amount of modifier in the extraction vessel enhanced the recovery approximately 30% for progesterone, phenanthrene, and pyrene due to a "co-extraction effect".     

Bubbles pinned on electrodes: Friends or foes of aqueous electrochemistry?

Electrochemists and engineers regard adherent gas bubbles as redox-inactive and therefore blocking entities. Adhesion of bubbles at electrodes generally carries an energy penalty. But this is not always the case: bubbles pinned on an electrode surface initiate the oxidation of water-soluble species under conditions where such reactions would normally be considered impossible. Here we critically review the recent literature that is beginning to unveil the novel concept of on-water electrochemistry. Harnessing electrochemical reactivity of the water–gas–electrode interface has the potential to become a game-changer in organic electrosynthesis, accelerating the transition toward a sustainable chemical industry by simplifying the direct integration of renewable electricity into the production of commodity chemicals.