Superimposed transition mechanisms in polyvinylchloride

Summary Studies have been made of the viscoelastic behaviour of PVC in the glass-rubber transition by means of square and triangular periodic stresses, in order to find a plausible hypothesis on the appearing molecular mechanisms.In this respect it is obviously not possible to make a detailed analysis of the different types of mechanisms, based only on results from dynamic mechanical measurements. However, by using the general properties of the function logJ ₂ =g {logJ ₁} some ideas can be put forward.It is apparent that the viscoelastic behaviour stems from more than one single molecular mechanism. Simple segment movements dominate the behaviour only in the central part of the transition.At temperatures around the glass point an increase in losses and/or stiffness appears. It seems possible that this behaviour arises from the influence of the crystallites. At high temperatures a substantial increase in mechanical losses appears, which seems to be due to decomposition of widely spaced entanglements.In the plateau-zone a secondary dispersion appears which shows pronounced sensitivity to the processing conditions. At increased gelation ratio the value of the loss peak increases. As no changes in crystallinity have been observed, it is suggested that this dispersion originates from the decomposition of untrapped entanglements outside the network composed by the very small crystallites.With 4 figures     

Comparative Raman study of the Ti complex Cp2Ti(η2-C60) · C6H5CH3 and TixC60 films

Raman spectra from the first Ti fullerene complex Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ are presented. Compared to spectra of pure C₆₀, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C₆₀. The A _g(2) mode is downshifted by 12 cm⁻¹ compared to C₆₀, which corresponds to a charge transfer of one electron per Ti-C₆₀ bond. This value (6 cm⁻¹ for one transferred electron) is identical to the downshift of the A _g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ were compared to the spectra of evaporated Ti_xC₆₀ films. The A _g(2) mode in Ti₄C₆₀ showed a downshift of about 25 cm⁻¹ compared to pure C₆₀, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η²-C₆₀-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.     

Mass spectrometric determination of tris(1,3-dichloro-2-propyl)-phosphate (TDCP) using NCI-technique

A number of different products suspected to contain flame retardants were analysed. TDCP was found in 11 out of 104 samples. It was most common in polyurethane products such as sound absorbing materials and liners for cars and buses. To get an integrated picture of TDCP exposure the contents of vacuum cleaner bags from two homes were analysed. One of these contained TDCP. To investigate possible presence in humans, blood samples were analysed. For clean-up, Sep-Pak cartridges with C18 phase were used. These cartridges contained TDCP and it was not possible to eliminate this background entirely. The NCIMS detection sensitivity for TDCP was better when analysing plasma extracts than when analysing pure standard solutions. Thus quantitative determinations of TDCP must be made by standard additions to plasma extracts. Something in the blood plasma seems to be able to bind or immobilise a certain amount of TDCP. Therefore it was not possible to analyse amounts less than 600 pg/ml whole blood with this method. None of the 37 analysed blood samples exceeded this value.     

The nature of the nonlinear anelasticity of glassy polymers

Nonlinearity in stress-strain behavior under conditions where the strain is completely recoverable is often observed in glassy amorphous polymers. In the present work a suggestion is made that the nonlinearity is often associated with a secondary (β) relaxation process. By means of a model calculation it is shown that the onset of stress saturation of the relaxed or equilibrium compliance associated with localized group motion is a reasonable explanation for the phenomenon. The effect of stress on relaxation times is predicted to have some contribution but to be less important than the effect on the relaxed compliance.     

Autocorrelations between pseudo-random numbers

In this paper some generating methods of the multiplicative and mixed congruential types for obtaining pseudo-random numbers are reviewed. Procedures to determine autocorrelations are demonstrated and a few numerical results are also given.     

All alkoxide route to manganate and coboltate perovskite films and powders: effects of processing parameters

Manganate and cobaltate perovskites having the general formula ABO₃ have many technologically important applications. Here we present all alkoxide based routes to manganate and coboltate perovskite films and nano-phase powders of the compositions; LCMO (La_0.67Ca_0.33MnO₃), LSMO (La_0.75Sr_0.25MnO₃), LNCMO (La_0.33Nd_0.33Ca_0.33MnO₃), LBSMO (La_0.75Ba_0.125Sr_0.125MnO₃) and LSCO (La_0.50Sr_0.50CoO₃). The Mn and Co (oxo) methoxy-ethoxide precursors were prepared by reaction of MnCl₂ or CoCl₂ with 2 Kmoe in methoxy-ethanol-toluene. After hydrolysis of the alkoxide solutions by atmospheric air all systems produced X-ray and electron diffraction amorphous gels of high elemental homogeneity, and the IR spectra showed that they consisted of hydrated oxo-carbonates. Heating in air resulted in similar weight-loss curves for all studied gels passing; loss of H₂O in the range 20–300 °C, decomposition of carbonate groups into oxide and CO₂ in the temperature range 300–700 °C, and in some cases loss of a small amount of oxygen in the temperature range 700–1,000 °C. The pure perovskites were obtained at 690–770 °C with heat rates of typically 5–20 °C min^?1 without annealing. Perovskites could also be obtained at 550 °C by annealing, but these perovskites are prone to be A-site ion inhomogeneous according to the TEM EDS studies, which was not the case for the perovskites heat-treated to at least the carbonate decomposition temperature. This A-site inhomogeneity is ascribed to sequential decomposition of carbonates due to their different thermal stabilities, which is probably a general feature also with other sol–gel precursors and low temperature annealing. High quality polycrystalline films were prepared on Si/SiO₂/TiO₂/Pt substrates with all compositions and high quality epitaxial films were prepared of LCMO (on 100 LaAlO₃) and LSCO (on 100 SrTiO₃). The colossal magneto resistance (CMR) of the epitaxial LCMO films of 32% (246 K) is in parity with PLD derived films. The conductivities of the epitaxial and polycrystalline LSCO films were 1.9 mΩcm (on STO) and 1.7 mΩcm (on α-Al₂O₃, respectively).     

Interactions of neutral and singly charged keV atomic particles with gas-phase adenine molecules

KeV atomic particles traversing biological matter are subject to charge exchange and screening effects which dynamically change this particle's effective charge. The understanding of the collision cascade along the track thus requires a detailed knowledge of the interaction dynamics of radiobiologically relevant molecules, such as DNA building blocks or water, not only with ionic but also with neutral species. We have studied collisions of keV H(+), He(+), and C(+) ions and H(0), He(0), and C(0) atoms with the DNA base adenine by means of high resolution time-of-flight spectrometry. For H(0) and H(+) we find qualitatively very similar fragmentation patterns, while for carbon, strong differences are observed when comparing C(0) and C(+) impact. For collisions with He(0) and He(+) projectiles, a pronounced delayed fragmentation channel is observed, which has not been reported before.     

Parameters affecting microwave-assisted extraction of organophosphorus pesticides from agricultural soil

This work describes an optimised method for the determination of six representative organophosphorus pesticides (OPPs) (diazinon, parathion, methyl pirimiphos, methyl parathion, ethoprophos, and fenitrothion) in agricultural soils. The method is based on microwave-assisted extraction using a water-methanol modified mixture for desorption and simultaneous partitioning on n-hexane (MAEP), together with gas chromatography-flame photometric detection (GC-FPD). To improve GC-FPD signals (peak intensity and shape) olive oil was used effectively as a "matrix mimic". The optimisation of the extraction method was achieved in two steps: an initial approach through experimental design and principal component analysis where recovery of compounds using a water-methanol mixture ranged from 54 to 77%, and the second one by studying the addition of KH2PO4 to the extracting solution where recoveries were significantly increased, molecular replacing of OPPs from adsorption sites by phosphate being the probable extraction mechanism. Under optimised conditions, recoveries of pesticides from different soils were higher than 73%, except for methyl parathion in some soils, with SD equal or lower than 11% and detection limits ranging from 0.004 to 0.012 microg g(-1). The proposed method was used to determine OPPs in soil samples from different agricultural zones of Chile.