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41.
Temperature Modulated DSC for the Investigation of Polymer Materials: A brief account of recent studies 总被引:1,自引:0,他引:1
Temperature modulated differential scanning calorimetry (TMDSC), the most recent development that adds periodic modulation to the conventional DSC, has recently seen a fast growth due to availability of commercial instrumentation. The use of the technique necessitates a total control of all of the experimental parameters. The paper focuses on recent applications to investigate polymers [1].This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
42.
Karger-Kocsis J. Shang P. P. Moskala E. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):21-28
The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential
scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization
and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing
deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly
higher glass transition temperature (Tg). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a
non-reversing part was considered as appearance of possible microcrystallinity. The Tg range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
43.
Analysis of the out-of-phase modulated photocurrent (MPC) signal, the so-called Y signal, is proposed for determining the trapping–detrapping events, recombination processes and gap-state parameters in amorphous silicon. This is demonstrated by analysing experimental Y spectra obtained on this material from different laboratories including our own. Model simulations are also employed in which the amphoteric nature of the dangling bonds and their distribution according to the defect-pool model are taken into account. From the reconstruction of the Y signal, phase shift and MPC amplitude spectra, several contributions resolved from the frequency dependence of the experimental Y spectra are identified. Two electron trapping–detrapping processes are resolved. These are attributed to hydrogen-related positive defects and to transitions involving the D+/0 level of the normal dangling bonds from the defect-pool distribution. At lower frequencies a residual contribution is resolved that is attributed to a term related to recombination through the D+/0 and D0/? levels. Between 300 and 150?K the above recombination contribution is essentially from the D0/? and dominates the Y signal at lower frequencies. In this region a characteristic phase lead appears, which is attributed to the existence of safe hole traps in the valence band tail. Around 150?K, trapping–detrapping events in the conduction band tail dominate. 相似文献
44.
45.
Steven Swier Kurt Van Durme Bruno Van Mele 《Journal of Polymer Science.Polymer Physics》2003,41(15):1824-1836
The heat capacity or reversing heat flow signal from modulated‐temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three‐phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi‐isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time‐dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi‐isothermal demixing and remixing measurements is also examined in the time domain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1824–1836, 2003 相似文献
46.
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48.
杨秀绘 《数学物理学报(B辑英文版)》2011,31(4):1272-1280
This paper is concerned with the quasi-neutral limit of the bipolar NavierStokes-Poisson system. It is rigorously proved, by introducing the new modulated energy functional and using the refined energy analysis, that the strong solutions of the bipolar Navier-Stokes-Poisson system converge to the strong solution of the compressible NavierStokes equations as the Debye length goes to zero. Moreover, if we let the viscous coefficients and the Debye length go to zero simultaneously, then we obtain the convergence of the strong solutions of bipolar Navier-Stokes-Poisson system to the strong solution of the compressible Euler equations. 相似文献
49.
Viñas P Martínez-Castillo N Campillo N Hernández-Córdoba M 《Journal of chromatography. A》2011,1218(5):639-646
A miniaturized liquid-phase extraction procedure based on directly suspended droplet microextraction is proposed for determining different classes of polyphenols. A derivatization reaction by means of in injection-port reaction with bis(trimethylsilyl)trifluoroacetamide is carried out to convert the polar non-volatile polyphenols into volatile derivatives. The separation and detection is carried out by coupling gas chromatography with mass spectrometry in the selected ion monitoring mode. The procedure uses undecanone, a low density organic solvent, and several factors influencing the extraction, collection efficiency and derivatization reaction are optimized. Excellent linearity was obtained for the range studied (0.05-500ngmL(-1)). The limits of detection are between 0.011 and 0.13ngmL(-1), depending on the compound, and the limits of quantification between 0.037 and 0.43ngmL(-1). The sensitivity and detection limits for polyphenols using the DSDME sample pretreatment method were very low. Enrichment factors are between 413 and 578. The recoveries obtained for spiked samples are satisfactory for all the compounds. The coupled miniaturized method is applied to the sensitive determination of both cis- and trans-resveratrol isomers, piceatannol, catechin, epicatechin, quercetin and fisetin in herbal infusions, fruits, juices and functional foods. 相似文献
50.
In this paper, we obtain sufficient and necessary conditions for local asymptotics for the maximum of a Markov modulated random
walk with long-tailed increments and negative drifts, where the local asymptotics means asymptotic behaviour of P(· ∈ (x, x + z]) for each z > 0, as x→∞. Our results extend and improve the existing ones in the literature. 相似文献