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101.
R. Sabater i Serra A. Kyritsis J. L. Escobar Ivirico J. L. Gómez Ribelles P. Pissis M. Salmerón-Sánchez 《The European physical journal. E, Soft matter》2011,34(4):37
Poly( e \varepsilon -caprolactone)/poly(hydroxyethyl acrylate) networks have been investigated by thermally stimulated depolarization currents
(TSDC) and differential scanning calorimetry (DSC). The introduction of hydrophilic units (HEA) in the system aiming at tailoring
the hydrophilicity of the system results in a series of copolymer networks with microphase separation into hydrophobic/hydrophilic
domains. Polycaprolactone (PCL) crystallization is prevented by the topological constraints HEA units imposed in such heterogeneous
domains. Moreover, the mobility of the amorphous PCL chains is enhanced as revealed by the main relaxation process which becomes
faster. The glass transition of PHEA-rich domains shifts to lower temperatures, as the total amount of PCL in the copolymer
increases, due to the presence of PCL units within the same region. The behaviour of the copolymer networks swollen with different
content of water has been investigated to analyze the interaction between water molecules and hydrophobic/hydrophilic domains
and provide further insights into the molecular structure of the system. 相似文献
102.
Polymer segmental dynamics and solvent thermal transitions in poly(ethyl acrylate)/p‐xylene mixtures
A. T. Stathopoulos A. Kyritsis F. J. Romero Colomer J. L. Gomez Ribelles N. Shinyashiki C. Christodoulides P. Pissis 《Journal of Polymer Science.Polymer Physics》2011,49(6):455-466
A poly(ethyl acrylate) polymer network was swollen with different concentrations of the nonpolar solvent p‐xylene, cpx, from xerogel until saturation (0 ≤ cpx ≤ 0.85). Differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) techniques were employed to study the polymer segmental dynamics and the solvent thermal transitions in homogeneous (cpx < 0.20) and partially crystallized (cpx ≥ 0.20) PEA/p‐xylene mixtures. Our DSC measurements indicate that p‐xylene undergoes cold crystallization for intermediate solvent concentrations, 0.20 ≤ cpx ≤ 0.30 while for higher cpx values crystallization takes place during cooling. The results show that for cpx ≤ 0.30 the Tg decreases with increasing cpx (plasticization effect) obeying the respective Fox equation. For the same cpx range we found that both the dielectric strength and the heat capacity increment of the segmental (α) relaxation process increase gradually with cpx whereas the distribution of relaxation times for the underlying molecular relaxations does not change. For cpx > 0.30 the partially crystallized mixtures exhibit a constant Tg corresponding to the gel phase of PEA with an amount of p‐xylene which is not able to crystallize under any conditions. The concentration of this noncrystallized p‐xylene, cUCpx, has been estimated to be between 0.12 and 0.15, independent of the total p‐xylene concentration in the mixtures. When a separate p‐xylene crystal phase is formed (for cpx > 0.30) the segmental dielectric strength and heat capacity increment decrease significantly exhibiting values significantly lower than those measured for the homogeneous gels. In addition, we found that the presence of p‐xylene crystals may induce marginal spatial heterogeneity of polymer (or p‐xylene) concentration within the gel phase affecting thus slightly the breath of the segmental relaxation of PEA. We attribute these results to restrictions of polymer segmental configurations due to constraints imposed by the p‐xylene crystals and/or to the immobilization of a part of the polymer chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
103.
Nikolaos S. Thomaidis Efrosini A. Piperaki Panayotis A. Siskos 《Mikrochimica acta》1995,119(3-4):233-241
A procedure for the determination of the aqua regia soluble content of lead, cadmium and chromium in a sewage sludge reference material (CRM 145R) by electrothermal atomic absorption spectrometry (ETAAS) is described. A comparison of the dissolution procedure proposed in the certification report, to an oven-assisted digestion and a proposed microwave digestion procedure is performed. In the ETAAS method developed, 1 g of Pt proved to be an appropriate modifier for each of the above heavy metals. Possible sources of error at each analytical step are addressed. The metal contents obtained with the proposed method are in a good agreement at 95% significance level with the certified values given for CRM 145R. 相似文献
104.
Flame propagation speeds in compositionally stratified methane–air mixtures were theoretically calculated as a function of the equivalence ratio distribution in the unburnt mixture and compared with experimental results. A solution of non-adiabatic flame propagation under a quasi-steady approximation was able qualitatively to describe the experimentally observed characteristics of flame speeds in stratified mixtures, which were flame speed increase in the vicinity of the flammability limits as well as for high equivalence ratio gradients. However, this analysis failed to provide quantitative agreement with the experimental results. In order to address this, the cumulative heat support effects on flame temperature, depending on the history of flame propagation, had to be accounted for. Quantitative agreement with the experiments was achieved, especially for propagation in lean mixtures. 相似文献
105.
We report the results of detailed investigations of polymer-water interactions and of the organization of water in the poly(ethylene oxide) (PEO)/water system by dielectric techniques. They include thermally stimulated depolarization currents (TSDC) techniques in the temperature range of 77-300 K and broadband dielectric relaxation spectroscopy (DRS) techniques of frequencies, 5 Hz-10 GHz, and temperatures, 173-300 K. The water content h was varied between 0 and 1.21 (grams of water per gram of dry PEO). The secondary γ mechanism of PEO and the reorientation of absorbed water molecules were extensively studied. The γ mechanism was found to be plasticized up to water contents of about 0.20. The reorientation of water molecules was studied in three different experiments and frequency/temperature regions. The results suggest strong interactions in the PEO/water system and indicate the presence of a separate water phase at high water contents. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1545–1560, 1997 相似文献
106.
Joseph I. Degraw Panayotis Tsakotellis Roy L. Kisliuk Yvette Gaumont 《Journal of heterocyclic chemistry》1971,8(1):105-110
The syntheses of 10-deazapteroic and 11-deazahomopteroic acids are described. These compounds along with their simple 6-phenylalkylpteridinol relatives were found to be inactive as antimalarial agents against the Plasmodium berghei or Plasmodium gallinaceum strains. 10-Deazapteroie acid was a potent growth inhibitor of Streptococcus faecium both in the pteridine and tetrahydropteridine forms. 相似文献
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110.
J. B. Alexander Ross William R. Laws John Clark Sutherland Angeliki Buku Panayotis G. Katsoyannis Irving L. Schwartz Herman R. Wyssbrod 《Photochemistry and photobiology》1986,44(3):365-370
A linked-function approach to fluorescence decay data analysis is presented that permits complex systems to be resolved from a single decay curve. The method involves linking fluorescence decay parameters based on a relationship established by independent physical measurements. As an example, by correlating the fluorescence data with 1 H-NMR results, the complex fluorescence decay kinetics of tyrosine analogs and single tyrosyl residues in simple polypeptides can be explained by ground-state rotameric populations of the phenol ring about the Cα-Cβ bond. 相似文献