The Distortion of Electrically Conducting,Thermodynamically Stable Microphases by an Electric Field

O'Konski's considerations regarding the distortion of spherical droplets by electric fields in binary two-phase systems has been extended to three-component water/surfactant/oil systems with so-called ultra-low interfacial tensions, i.e. spherically aqueous microphases. It is shown that the deformation is almost negligible for fields up to about 5 10⁵ Vm^?1 such as those applied in electro-optical Kerr-effect measurements with microemulsions if only perturbations of the mean orientation of the surfactants in the interface are considered.     

Circular dichroism analysis of penicillin G acylase covalently immobilized on silica nanoparticles

Circular dichroism (CD) was used to characterize the secondary structure of penicillin G acylase upon covalent immobilization on silica nanoparticles. Covalent immobilization was achieved by functionalizing the silica nanoparticles with glutardialdehyde and coupling to the free NH(2) groups of the enzyme (lysine and arginine side chains). The loading of the covalently bound enzyme was increased up to saturation, which was reached at 54.6 mg immobilized enzyme per g silica nanobeads. For structural characterization of the commercially available enzyme its exact molecular mass was determined by mass spectrometry in order to enable precise evaluation of the CD data. The fraction of secondary structure elements of the free and immobilized enzyme were estimated from the respective CD spectra using standard algorithms (CONTINLL, CDSSTR, SELCON3). The fractions obtained by the different algorithms for the free enzyme agreed well with one another and also with data from X-ray diffraction described in the literature. Interestingly, the secondary structure fractions found for the immobilized enzyme were very similar to the free enzyme and nearly constant over all experiments. These results indicate that even a loading of up to 55.8 mg/g (enzyme per silica nanoparticles) causes only slight structural changes. However, the specific activity determined by a kinetic assay decreased by around 60%, when increasing the loading from 14.9 to 55.8 mg/g. Because of the fact that we found no major changes in the secondary structure, diffusion limitation seems to be the main reason for the decline of the specific activity.     

X‐ray excited optical luminescence from crystalline silicon

Synchrotron based X‐ray excited optical luminescence (XEOL) has been measured with many direct bandgap semiconductors. We present XEOL measurements on crystalline silicon (Si), obtained despite of its indirect bandgap and the consequently low luminescence efficiency. Spectra of monocrystalline and multicrystalline (mc) Si at room temperature are compared to theoretical spectra. A possible application in the synchrotron‐based research on mc‐Si is exemplified by combining XEOL, X‐ray fluorescence (XRF) spectroscopy, photoluminescence (PL) spectroscopy, and microscope images of grain boundaries. This approach can be utilized to investigate the recombination activity of metal precipitates, to analyze areas of different lifetimes on mc‐Si samples and to correlate additional material parameters to XRF measurements. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonmonotonic pattern of the critical percolation temperature due to variations of additive chain length in water-in-oil microemulsions

The nonmonotonic variation of the critical percolation temperature (T _c) of ternary nonionic (C₁₄E₅) water-in-oil microemulsions was studied as a function of the alkyl chain length of an ionic additive (n-alkyl sulfonate sodium salt). A thermodynamic approach shows the relationship between T _c and additive chain length, which is supplemented by a consideration of a possible molecular mechanism of the observed phenomenon. Received: 20 October 2000 Accepted: 7 November 2000     

Dielectric Properties of Apolar Micelle Solutions Containing Solubilized Water

Varying amounts of water have been solubilized in a micelle solution of sodium di-2-pentyl–sulfoscuccinate in benzene and the complex permittivity has been observed in the range 200 KHz to 10 MHz. Part of a dielectric dispersion is seen, which extends to higher frequencies with a broad distribution of relaxation times. Due to association processes, the static dielectric increment is found to vary non-linearly with hydrated micelle concentration and with the amount of solubilized water, whereas a linear variation with micelle concentration is found if no water is added. These effects are explained on the assumption that part of the solubilized water increases the dipole moment of the micelle. Additionally, at higher water concentrations, a sudden increase in the conductivity of the solution is observed, which is taken to indicate a conformational change of the solubilized micelle.     

Electrical properties of planar bimolecular surfactant membrane

Planar bimolecular film of the triple long-chain salt(dihexadecyldimethylammonium hexadecanesulfonate) was found to be formed in the electrolyte solutions was carried out at different temperatures by the transient D. C. method. In four electrolyte solutions of Li⁺, Na⁺, K⁺, and Cs⁺ chlorides, the resistance of the membrane was very high (up to 10⁷ ohm·cm²). From the temperature-dependence of conductivity, the activation energy of ion transfer through the film was calculated by the Arrhenius equation. The magnitude of the activation energy was related with the size of the crystallographic radius.The authors acknowledge financial support from the Swiss National Science Foundation.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

Transition metals in silicon

A review is given on the diffusion, solubility and electrical activity of 3d transition metals in silicon. Transition elements (especially, Cr, Mn, Fe, Co, Ni, and Cu) diffuse interstitially and stay in the interstitial site in thermal equilibrium at the diffusion temperature. The parameters of the liquidus curves are identical for the Si:Ti — Si:Ni melts, indicating comparable silicon-metal interaction for all these elements. Only Cr, Mn, and Fe could be identified in undisturbed interstitial sites after quenching, the others precipitated or formed complexes. The 3d elements can be divided into two groups according to the respective enthalpy of formation of the solid solution. The distinction can arise from different charge states of these impurities at the diffusion temperature. For the interstitial 3d atoms remaining after quenching, reliable energy levels are established from the literature and compared with recent calculations.