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91.
The dipole dynamics and α-relaxation behaviour of polyvinyl chloride PVC, poly(ethylene-co-vinyl-acetate) EVA70 and blend of them EVA70/PVC have been investigated by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). The differential scanning calorimetry (DSC) thermograms measured on samples show a single glass transition in the analysed temperature range. These three polymers are wholly amorphous and pure PVC and pure EVA70 are miscible in the ratio 1:1. The glass transition temperature Tg decreases significantly with presence of EVA70. Furthermore, the values of apparent activation energies for molecular motions at the α-relaxation and the values of fragility index have also been determined for each sample using Moynihan expression for DSC results and Vogel-Fulcher-Tammann-Hesse (VFTH) form for DRS results. It is shown a large dependence of all the values of these parameters with the content of EVA70. Comparing these three polymers, we found that the more fragile glass forming liquid is the PVC. Fragility decreases drastically with EVA70 content. EVA70 and EVA70/PVC blend exhibit practically the same behaviour. The effect of inter- and intra-molecular interactions on fragility is discussed to explain these variations. 相似文献
92.
Udo Kaatze 《Journal of solution chemistry》1997,26(11):1049-1112
A tutorial on dielectric (relaxation) spectrometry of liquids is given in this article. Some methods of measuring complex
(electric) permittivity spectra are briefly described. Results for water are presented and related to characteristic properties
of the liquid structure and to models of the molecular dynamics, particularly as resulting from computer simulation studies.
Dielectric spectra for aqueous solutions of low weight electrolytes, polyelectrolytes, small molecules, and polymers are discussed
to illustrate effects of kinetic depolarization, structure saturation, as well as positive, negative, and hydrophobic hydration.
Reference is also made to fluctuations in the hydrogen bond network of mixtures of water with liquids that are completely
miscible with this unique solvent. 相似文献
93.
A comparative quantum-chemical analysis of the electronic structures and spectroscopic parameters of the cycloalkanes C3H6, C4H8, C5H10, and C6H12 and their silicon analogs Si3H6, Si4H8, Si5H10 and Si6H12 was performed in the framework of the SCF MO LCAO method in the INDO approximation. Qualitative interpretation of “abnormal”
ionization potentials and energies of electronic absorption spectra of cyclopolysilanes has been given.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1997. 相似文献
94.
The vertical ionization potentials of bis(-allyl)nickel (see (1) in Fig. 1) are calculated by means of the Green's function approach within a semiempirical INDO extension to the first transition metal series. The computed ionization potentials are in good agreement with an experimentally deduced assignment. In contrast to earlier theoretical and experimental studies, the 7a
u
() level is predicted on top of the levels corresponding to the Ni 3d orbitals. Our approach leads to a complete assignment of the PE spectrum of (1) in the outer valence region. 相似文献
95.
Polystyrenes with different concentrations of side groups with cyano groups were prepared and complex dielectric constants were measured in the range of the glass transition temperature and the frequency range of 10–2–107 Hz.The GPC and DSC measurements showed that the molecular weight of these polystyrenes was about 10500 g/mole and the glass transition temperatures were 89.5°C for all samples.The dielectric relaxation spectra obtained for the side group polystyrene labels and also the chain-end polystyrene labels prepared before [9] were analyzed to find out the degree of coupling of the chain-end and side-group labels with the cooperative reorientation of the polymeric matrix. The analysis of the spectra was carried out using the analysis method developed by Mansour and Stoll [6].The results obtained showed that both end- and side-group labels are strongly coupled with the segmental reorientation and relax with relaxation times longer than that of the segments.The value of logf
m = (logf
m(label)) – logf
m(matrix)) was obtained from the recently designed comparison diagram suggested by Mansour and Stoll [6, 14]. The value of logf
m depends on the label length in the case of chain-end labels.It was surprising to find that the side groups relax slower than the segments by only 0.9 decades. These results obtained implied that the label relaxes through a multistep relaxation mechanism of the side and end groups and not through a diffusion mechanism of the whole chain. In addition, the effective lengths of the relaxing units were determined using the empirical equation obtained before in the case of rodlike molecules in polyisoprene [7]. 相似文献
96.
Chemical reactions occurring at the mineral–water interface are controlled by an interfacial layer, nanometers thick, whose properties may deviate from those of the respective bulk mineral and water phases. The molecular-scale structure of this interfacial layer, however, is poorly constrained, and correlations between macroscopic phenomena and molecular-scale processes remain speculative. The application of high-resolution X-ray scattering techniques has begun to provide substantial new insights into the molecular-scale structure of the mineral–water interface. In this review, we describe the characteristics of synchrotron-based X-ray scattering techniques that make them uniquely powerful probes of mineral–water interfacial structures and discuss the new insights that have been derived from their application. In particular, we focus on efforts to understand the structure and distribution of interfacial water as well as their dependence on substrate properties for major mineral classes including oxides, carbonates, sulfates, phosphates, silicates, halides and chromates. We compare these X-ray scattering results with those from other structural and spectroscopic techniques and integrate these to provide a conceptual framework upon which to base an understanding of the systematic variation of mineral–water interfacial structures. 相似文献
97.
98.
Residual stress in the epoxy plate during a rapid cooling process was measured by the layer removal method and calculated by the linear thermoviscoelastic theory considering specific volume relaxation. The relaxations of the tensile modulus and specific volume were measured by an Instron thermomechanical analyzer. When the starting temperature of the cooling process was near the glass transition temperature of the cured epoxy, the residual stress in the epoxy plate was smaller than when the starting temperature was higher than the glass transition temperature. However, the transient stress in the cured epoxy plate was higher when the starting temperature was near the glass transition temperature than when the starting temperature was higher than the glass transition temperature. The quenched epoxy plate was compressed in the direction parallel to the surface and expanded in the thickness direction. 相似文献
99.
Proton relaxation rates of the solvent water in NaClO4, NaBF4, LiClO4, and NiBF4 solutions together with some self-diffusion coefficients are reported and interpreted in terms of structure-breaking effects.19F relaxation rates in7LiBF4 and6LiBF4 solutions in D2O have been measured, and the relaxation contribution caused by7Li+ has been evaluated to give a cation-anion model pair distribution function.7Li relaxation rates in H2O and D2O are also reported, and conclusions concerning the hydration structure of Li+ have been drawn. The strong relaxation effects caused by the ions BF
4
–
and ClO
4
–
on23Na+ and7Li+ have been subjected to a detailed analysis, and combined ion-solvent encounter configurations are presented which yield an electric field gradient strong enough to cause the observed effect.Part 1 was presented at the Faraday Discussion Ion-Ion and Ion-Solvent Interaction, Oxford, September 1977 (see ref. 1). 相似文献
100.
The tube model is applied for the treatment of stress-strain measurements on SBR networks. It is shown that this theory allows the separation of crosslink and constraint contributions to the stress-strain behavior and, also, a reliable determination of crosslink densities. The consideration of dynamical contributions is discussed and a special numerical method is developed. 相似文献