Glass transition temperature dependence on heating rate and on ageing for amorphous selenium films

The study, by differential thermal analysis (DTA) of the glass transition of thermally evaporated amorphous selenium, allows the effect of ageing on structural properties to be observed. An enthalpic diagram is used to explain the shift of the glass transition region, with heating rate, and also with ageing. These shifts are directly dependent on structural relaxation in amorphous selenium. The model used, to express the change of the structural time relaxation with temperature, and with the departure of thermodynamic equilibrium leads to a slightly different expression for the dependence of T_g on heating rate than that previously published (by Moynihan et al.).The activation enthalpies of the studied phenomena compared with other results, seem to show that structural relaxation in a-Se principally involves bond breaking and reformation of chains.     

THERMODYNAMIQUE DES ENSEMBLES DE CANTOR AUTOSIMILAIRES（THERMODYNAMICS OF SELF-SIMILAR CANTOR SETS）

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Fine-tuning the transition temperature of a stimuli-responsive polymer by a simple blending procedure

Binary mixtures of well-defined, stimuli-responsive elastin-based side-chain polymers show a single transition temperature that depends on blend composition.     

Solute-induced perturbations of solvent-shell molecules observed using multivariate Raman curve resolution

Raman spectral features associated with the reorganization of solvent molecules around a solute are obtained using multivariate curve resolution. Spectra collected from solutions of variable concentration are resolved into unperturbed and perturbed components assuming only that the spectra and concentrations of each component are non-negative (with no peak-fitting or constraints on the shapes of either the perturbed or unperturbed spectral features). The capabilities of the method are demonstrated using solutions of acetonitrile, acetone, and pyridine in water as well as acetonitrile and cyclohexane in 1,2-dichloroethane (DCE). The results reveal vibrational spectra of solvation-shell molecules that are perturbed by each solute. The perturbed solvent-shell water molecules are found to have different OH stretch bands (of higher frequency and narrower width than bulk water), and the gauche-trans equilibrium of solvent-shell DCE molecules are perturbed in opposite directions by the polar and nonpolar solutes.     

Synthesis of cyclomanganated complexes derived from 2,5-diphenyl-1,3,4-oxadiazole and their reactivity with respect to 1,1-diphenyldiazomethane: Evidence for a fluxional trihaptobenzylic coordination mode

The cyclometallation of 2,5-diphenyl-1,3,4-oxadiazole with benzylpentacarbonylmanganese afforded the related mono- and binuclear complexes. The thermolytic coupling of 1,1-diphenyldiazomethane with monometallated 2,5-diphenyl-1,3,4-oxadiazole afforded substantial amounts of a new trihaptobenzylic complex. In the solid state, an X-ray diffraction analysis confirmed the coordination of manganese metal to one of the phenyl groups introduced by the 1,1-diphenyldiazomethane and to one of ligand’s nitrogen centre. In solution, this trihaptobenzylic complex displays a fluxionality which is assumed to be related to the equilibration of its helical Λ and Δ enantiomers.     

Non-isothermal crystallization in amorphous selenium films

The usual determination of kinetic parameters of crystallization of amorphous products is based on isothermal measurements. In general the crystallization of amorphous selenium thin films is studied by non-isothermal experiments (DTA). The adaptation to non-isothermal crystallization of the Avrami transformation rate equation allows us to determine different types of crystallization. These different regions enable one to determine the variations of the growth rate and of the nucleation rate versus temperature. The influence of the wavelength of illumination during the crystallization time on these parameters is also investigated.

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Zusammenfassung Die übliche Bestimmung kinetischer Parameter der Kristallisation amorpher Produkte basiert auf isothermen Messungen. Die Kristallisation von amorphem Selen in dünnen Schichten wird im allgemeinen in nicht-isothermen Experimenten (DTA) untersucht. Die Adaptation der Transformationsgeschwindigkeitsgleichung nach Avrami an die nicht-isotherme Kristallisation ermöglicht die Bestimmung verschiedener Kristallisationtypen. Dadurch wird es möglich, die Veränderungen der Wachstumsgeschwindigkeit und der Geschwindigkeit der Nukleation in Abhängigkeit von der Temperatur zu bestimmen. Der Einfluß der Wellenlänge bei der Bestrahlung während der Kristallisation auf diese Parameter wird ebenfalls untersucht.

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Lubricated squeezing flow of thin slabs of wheat flour dough: comparison of results at constant plate speed and constant extension rates

Lubricated squeezing flow experiments on wheat flour dough have, until now, mostly been performed in constant plate speed mode (CPS), i.e. at a permanently increasing extension rate. We have compared the results obtained under the CPS and constant extension rate (CER) modes using one of the very few commercial rheometers that allow operation in the CER mode. In both cases, and at any constant biaxial strain, a power law could be fitted to the stress versus extension rate data, the “consistency index” (K) increasing continuously with the strain and the “flow behaviour index” (n) being constant only up to a low strain value (≈0.25) and then decreasing. When compared to the CER mode, the CPS mode produced higher K and n values. For wheat flour doughs, an increase in K with extension may be associated to a strain-hardening phenomenon but the roles of viscoelasticity and lubricant thinning are discussed.     

The escape factor in plasma spectroscopy—IV the case of an overlapping doublet

The conditions under which the escape factor technique may be used to describe photo-excitation within the individual components of an overlapping doublet with a common lower state are derived and are found to be violated in a differentially moving plasma such as a laser-produced plasma. Model calculations are presented for the hydrogen-like L_α doublet, which is currently of interest with laser-produced plasmas.