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1.
Indium was analyzed with both, standard differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) using
sinusoidal and saw-tooth modulation. Instrument and sample effects were separated during nucleated, reversible melting and
crystallization transitions, and irreversible crystallization with supercooling. The changes in heat flow, time, and sample
and reference temperatures were correlated as functions of heating rate, mass, and modulation parameters. The transitions
involve three regions of steady state (an initial and a final region before and after melting/crystallization, a region while
melting/crystallization is in progress) and one region of approach to steady state (melting peak to final steady state region).
Analyses in the time domain show promise when instrument lags, known from DSC, are used for correction of TMDSC. A new method
of integral analysis is introduced for quantitative analysis even when irreversible processes occur in addition to reversible
transitions. The information was derived from heat-flux calorimeters with control at the heater block or at the reference
temperature sensor.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
The Relationship Between the TMDSC Curve of Frozen Sucrose Solutions and Collapse During Freeze-Drying 总被引:1,自引:0,他引:1
Knopp S. A. Chongprasert S. Nail S. L. 《Journal of Thermal Analysis and Calorimetry》1998,54(2):659-672
This study compares measurements of the collapse temperature of sucrose solutions by freeze drying microscopy with features
of TMDSC curves both in the scanning and quasi-isothermal modes. The objective was to determine which feature of the TMDSC
curve is predictive of collapse and to provide additional evidence for recent interpretations of the physical significance
of the low temperature transitions for sucrose solutions. Interpretations based on the heat capacity signal and the kinetic
heat flow using TMDSC are consistent with previous reports based on total heat flow measurement, where the lower temperature
transition is the glass transition and the higher temperature transition is associated with the onset of ice melting. Quasi-isothermal
experiments further support these conclusions, since additional crystallization of ice is observed only in the region of the
lower temperature transition. Collapse of sucrose solutions during freeze-drying begins at the approximate midpoint between
the end of the glass transition region and the onset of ice melting.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Temperature modulated dynamic mechanical analysis (TMDMA) was performed in the same way as temperature modulated DSC (TMDSC)
measurements. As in TMDSC TMDMA allows the investigation of reversible and non-reversible phenomena during crystallisation
of polymers. The advantage of TMDMA compared to TMDSC is the high sensitivity for small and slow changes in crystallinity,
e.g. during re-crystallisation. The combination of TMDMA and TMDSC yields new information about local processes at the surface
of polymer crystallites. It is shown that during and after isothermal crystallisation the surface of the individual crystallites
is in equilibrium with the surrounding melt.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
In this paper we present a new cooling system for temperature modulated DSC (TMDSC) working down to about 60 K. In order to demonstrate the features of this new system in combination with commercial TMDSC apparatus, we present measurements of the specific heat capacity (cp) around the phase transitions of betaine borate and betaine phosphate. For SilGel 604 we report cp and sound velocity data around the melt, as well as around the glass transition. 相似文献
5.
This paper provides an analysis of contributions to the apparent, reversing heat capacity when measured by temperature-modulated differential scanning analysis (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur. To deconvolute the data of a TMDSC scan into a total and reversing part, it is common practice to use the sliding averages and the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces erroneous reversing contributions which are detailed by experiment and simulation. Unless the response to the temperature modulation is linear, the total heat-flow rate is stationary, and the transition is truly reversible and occurs only once during the temperature scan, one cannot expect a true deconvolution of total and reversible effects. In the presence of multiple, irreversible transitions within a modulation period, however, each process involving latent heat can increase the modulation amplitude, as demonstrated by computer-simulation of polymer melting. As a result, the multiple transitions may give erroneously high latent heats when integrating the apparent reversing heat capacity with respect to temperature. 相似文献
6.
The response of temperature-modulated differential scanning calorimetry (TMDSC) to irreversible crystallization of linear polymers was investigated by model calculations and compared to a number of measurements. Four different exotherms were added to a typical modulated, reversible heat-flow rate in order to simulate irreversible crystallization. It was found that the reversing heat-flow rate of the TMDSC in response to such irreversible crystallization exotherms is strongly affected by tbe shape of the transition and the phase-angle where the exotherm occurs. A comparison with the experimental data gave valuable insight into the transitions, as well as the nature of the TMDSC response which is usually limited to an analysis of the first harmonic term of the Fourier series that describes the heat-flow rate.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
7.
Temperature modulated dynamic mechanical analysis (TMDMA) was performed in the same way as temperature modulated DSC (TMDSC) measurements. Temperature modulation with amplitude 0.5 K and period 20 min was realised by a series of linear heating and cooling cycles (saw-tooth modulation). As in TMDSC TMDMA allows for the investigation of reversible and non-reversible phenomena in the melting and crystallisation region of polymers. The advantage of TMDMA compared to TMDSC is the high sensitivity for small and slow changes in crystallinity, e.g. during re-crystallisation. The combination of TMDMA and TMDSC yields new information about local processes at the surface of polymer crystallites. It is shown that during and after isothermal crystallisation the surface of the individual crystallites is in equilibrium with the surrounding melt. 相似文献
8.
Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal
TMDSC were used to analyze the protein–metallic ion interactions in silk fibroin proteins. The precise heat capacities were
measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment
through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the
silk–metallic salts system. Results show that K+ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (Tg) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca2+ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein
structure. This indicates that the thermal analysis methods offer a new pathway to study protein–metallic ion systems, yielding
very fruitful information for the study of protein structures in the future. 相似文献
9.
Javier Tarrío-Saavedra Carlos Gracia-Fernández Jorge López-Beceiro Salvador Naya Ramón Artiaga 《Journal of Thermal Analysis and Calorimetry》2012,109(3):1277-1284
The present study suggests a new approach, based on the utilization of temperature modulated differential scanning calorimetry (TMDSC) technique, for identifying and characterizing the organic?Cinorganic interphase of two materials: an epoxy?Cfumed silica nanocomposite and a thermoplastic polyurethane (TPU)?Cmultiwalled nanotube (MWNT) composite. The approach used here makes use of TMDSC data and basically consists of using the phase angle or the derivative of the reversing heat flow instead of the reversing heat flow curve itself. In the case of epoxy?Cfumed silica composites, two glass transition regions were identified. The glass transition temperature (T g) of the composite was observed to vary as a consequence of the filler content. This study shows that the T g variation is due to the formation of an organic?Cinorganic interphase, with its own glass transition temperature, which is different from the epoxy matrix T g. In the case of TPU?CMWNT composites, two relaxations and an additional first order transition were observed: the first relaxation corresponds to the hard segment, the second is related to an interaction between filler and matrix and the third process may be connected to the partial melting of the hard segment. The addition of 0.5?wt% MWNT causes a small reduction in T g of the TPU. A major nanotube addition, 10?wt%, induces the appearance of a new relaxation that may be associated with the existence of an interface. In general, a better separation between the matrix and interphase glass transitions was obtained by the TMDSC phase angle signal. 相似文献
10.
Sauer B. B. Kampert W. G. McLean R. S. Carcia P. F. 《Journal of Thermal Analysis and Calorimetry》2000,59(1-2):227-243
The thermal and crystal morphological properties of poly[ethylene teraphthalate] (PET) and poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) biaxially oriented films were compared to amorphous and other isotropic semi-crystalline samples. Crystal melting as a function of temperature was characterized by temperature modulated DSC (TMDSC) and found to begin just above the glass transition for both oriented films. About 75°C above the glass transitions, substantial exothermic recrystallization begins and continues through the final melting region in oriented films. The maximum in the non-reversing TMDSC signal for the oriented films signifies the maximum recrystallization exothermic activity with peaks at 248°C and 258°C for PET and PEN, respectively. The final melting endotherm detected was 260°C and 270°C for PET and PEN, and is shown by the TMDSC data and by independent rapid heating rate melting point determinations to be due to the melting of species recrystallized during the heating scan. The results are compared with TMDSC data for initially amorphous and melt crystallized samples. The volume fraction of rigid species (Frigid=total crystal fraction plus rigid amorphous or non-crystalline species) were measured by TMDSC glass transition data, and contrasted with the area fraction of rigid species at the oriented film surface characterized with very high resolution atomic force microscopy (AFM) phase data. The data suggest that the 11 nm wide hard domains in PET, and 21 nm wide domains in PEN film detected by AFM consist of both crystal and high stiffness interphase species.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
11.
Quasi-isothermal temperature modulated DSC and DMA measurements (TMDSC and TMDMA, respectively) were performed to determine
heat capacity and shear modulus as a function of time during crystallization. Non-reversible and reversible phenomena in the
crystallization region of polymers can be observed. The combination of TMDSC and TMDMA yields new information about local
processes at the surface of polymer crystals, like reversible melting. Reversible melting can be observed in complex heat
capacity and in the amplitude of shear modulus in response to temperature perturbation. The fraction of material involved
in reversible melting, which is established during main crystallization, keeps constant during secondary crystallization for
PCL PET and PEEK. This shows that also after long crystallization times the surfaces of the individual polymer crystallites
are in equilibrium with the surrounding melt. Simply speaking, polymer crystals are ‘living crystals’.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
示差扫描量热法(DSC)是表征材料热性能和热反应的一种高效研究工具,具有操作简便、应用广泛、测量值物理意义明确等优点.近年来DSC技术的发展大大拓展了高分子材料表征的测试范围,促进了对高分子物理转变的热力学和动力学的深入研究.温度调制示差扫描量热法(TMDSC)是DSC在20世纪90年代的标志性进展,它在传统DSC的线性升温速率的基础之上引入了调制速率,从而可将总热流信号分解为可逆信号和不可逆信号两部分,并能测量准等温过程的可逆热容.闪速示差扫描量热法(FSC)是DSC技术近年来的创新性发展,它采用体积微小的氮化硅薄膜芯片传感器替代传统DSC的坩埚作为试样容器和控温系统,实现了超快速的升降温扫描速率以及微米尺度上的样品测试,使得对于高分子在扫描过程中的结构重组机制的分析以及对实际的生产加工条件的直接模拟成为可能.本文从热分析基础出发,依次对传统DSC、TMDSC和FSC进行了介绍,内容覆盖其发展历史、方法原理、操作技巧及其在高分子表征中的应用举例,最后对DSC未来的发展和应用进行了展望.本文希望通过综述DSC原理、实验技巧和应用进展,帮助读者加深对DSC这一常用表征技术的理解,进一步拓展DSC表征高分子材料的应用. 相似文献
13.
C. A. Gracia-Fernández S. Gómez-Barreiro A. Álvarez-García J. López-Beceiro B. Álvarez-García S. Zaragoza-Fernández R. Artiaga 《Journal of Thermal Analysis and Calorimetry》2014,116(3):1273-1278
Dielectric analysis (DEA) is a very sensitive technique, which allows for detection of small structural changes at the low scale. An advantage of DEA, with respect to other modulated techniques, is the possibility of using a wider frequency range. Molecular relaxations of the order of only a few nanometers are not observed by any other thermoanalytic method. Nevertheless, these small relaxations involve dipole changes that can be observed by DEA. Thus, this technique is used here, in combination with temperature-modulated differential scanning calorimetry (TMDSC) to obtain insightful information about the thermal transitions of poly-l-lactic acid (PLLA), one of the stereo-isomers of polylactide. Its complex thermal behavior is the subject of ongoing debate, with several overlapping crystallization and melting processes. The combined use of TMDSC and DEA provides a better insight of three important transitions of this polymer: the alpha relaxation, the enthalpic relaxation, and the cold crystallization. The dependences of the enthalpy relaxation on the dynamic glass transition relaxation and on the glass transition as a thermal event are evaluated. On the other hand, it will be shown how the cold crystallization can be identified by TMDSC, and DEA helps us understand the effect of crystallization on the dipole movements. The shape of the dielectric permittivity curve at low frequencies is compared to that of the reversing heat capacity to check whether both signals are sensitive or not to the same events. It is also verified how the experimental results of alpha relaxation of PLLA follow an Arrhenius or a Vogel trend. 相似文献
14.
M. Pyda E. Nowak‐Pyda J. Heeg H. Huth A. A. Minakov M. L. Di Lorenzo C. Schick B. Wunderlich 《Journal of Polymer Science.Polymer Physics》2006,44(9):1364-1377
Quantitative temperature‐modulated differential scanning calorimetry (TMDSC) and superfast thin‐film chip calorimetry (SFCC) are applied to poly(butylene terephthalate)s (PBT) of different thermal histories. The data are compared with those of earlier measured heat capacities of semicrystalline PBT by adiabatic calorimetry and standard DSC. The solid and liquid heat capacities, which were linked to the vibrational and conformational molecular motion, serve as references for the quantitative analyses. Using TMDSC, the thermodynamic and kinetic responses are separated between glass and melting temperature. The changes in crystallinity are evaluated, along with the mobile–amorphous and rigid–amorphous fractions with glass transitions centered at 314 and 375 K. The SFCC showed a surprising bimodal change in crystallization rates with temperature, which stretches down to 300 K. The earlier reported thermal activity at about 248 K was followed by SFCC and TMDSC and could be shown to be an irreversible endotherm and is not caused by a glass transition and rigid–amorphous fraction, as assumed earlier. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1364–1377, 2006 相似文献
15.
I. Fraga S. Montserrat J. M. Hutchinson 《Journal of Thermal Analysis and Calorimetry》2008,91(3):687-695
The process of vitrification that occurs during the isothermal cure of a cross-linking system at temperatures below T
g∞, the glass transition temperature of the fully cured resin, has been studied by TOPEM, a new temperature modulated DSC (TMDSC)
technique based upon the use of stochastic temperature pulses. A comparison is made between TOPEM and another TMDSC technique,
and some advantages of TOPEM are considered. The TOPEM technique is used to show that the mobility factor is not always a
reliable approach to predicting the cure rate during vitrification, in view of its frequency dependence. Also, the dependence
of the apparent vitrification time on frequency is examined. There appears to be a non-linear relationship between the apparent
vitrification time and log(frequency), which is further discussed in the second part of this series. 相似文献
16.
Schick C. Merzlyakov M. Minakov A. Wurm A. 《Journal of Thermal Analysis and Calorimetry》2000,59(1-2):279-288
Quasi-isothermal temperature modulated DSC (TMDSC) were performed during crystallization to determine heat capacity as function of time and frequency. Non-reversible and reversible phenomena in the crystallization region of polymers were distinguished. TMDSC yields new information about the dynamics of local processes at the surface of polymer crystals, like reversible melting. The fraction of material involved in reversible melting, which is established during main crystallization, keeps constant during secondary crystallization for polycaprolactone (PCL). This shows that also after long crystallization times the surfaces of the individual crystallites are in equilibrium with the surrounding melt. Simply speaking, polymer crystals are living crystals. A strong frequency dependence of complex heat capacity can be observed during and after crystallization of polymers.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
17.
18.
Villaneuva M. Núñez Lisardo Núñez M. R. Rial B. Fraga L. Monsterrat S 《Journal of Thermal Analysis and Calorimetry》2002,70(1):45-56
The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (n=0) and 1, 2 diaminecyclohexane (DCH) with an epoxy reactive diluent vinylcyclohexane dioxide was studied by temperature modulated
differential scanning calorimetry (TMDSC). The models proposed by Kamal and by Horie et al. were employed in the kinetic study.
From these studies reaction orders, rate constants, and activation energies were determined. The technique of TMDSC allows
to include in the kinetic study the effect of diffusion by means of the mobility factor, calculated from the curves of the
complex heat capacity registered during the curing isothermal experiments. The results were compared to those obtained for
the same system employing the reaction rate data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
The heat capacity of poly(trimethylene terephthalate) (PTT) has been analyzed using temperature‐modulated differential scanning calorimetry (TMDSC) and compared with results obtained earlier from adiabatic calorimetry and standard differential scanning calorimetry (DSC). Using quasi‐isothermal TMDSC, the apparent reversing and nonreversing heat capacities were determined from 220 to 540 K, including glass and melting transitions. Truly reversible and time‐dependent irreversible heat effects were separated. The extrapolated vibrational heat capacity of the solid and the total heat capacity of the liquid served as baselines for the analysis. As one approaches the melting region from lower temperature, semicrystalline PTT shows a reversing heat capacity, which is larger than that of the liquid, an observation that is common also for other polymers. This higher heat capacity is interpreted as a reversible surface or bulk melting and crystallization, which does not need to undergo molecular nucleation. Additional time‐dependent, reversing contributions, dominating at temperatures even closer to the melting peak, are linked to reorganization and recrystallization (annealing), while the major melting is fully irreversible (nonreversing contribution). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 622–631, 2000 相似文献
20.
Temperature-modulated differential scanning calorimetry (TMDSC) has been used to study the melting of a series of blends containing
linear low-density polyethylene (LLDPE) and very low-density polyethylenes (VLDPE) with long chain branches. After the blends
were subjected to different thermal histories including thermal fractionation by stepwise isothermal cooling, they were examined
by TMDSC. TMDSC curves have been interpreted in terms of a combination of the reversing and non-reversing specific heats that
result from reversible and irreversible events at the time and temperature, which they are detected, respectively. It was
found that crystals formed at different crystallisation conditions had different internal order; hence they showed different
amounts of reversing and non-reversing contributions. There is no exothermic activity seen in the non-reversing signal for
the thermally fractionated polymers and their blends suggesting formation of crystals approaching equilibrium. In contrast,
polymers and blends cooled at 10°C min-1 cooling rate showed large exothermic contributions corresponding to irreversible effects. In addition, a true reversible
melting contribution is also detected for both fast-cooled and thermally-fractionated samples during the quasi-isothermal
measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献