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Modulated differential scanning calorimetry

III. Applications to measurements of the glass transition temperature and increment of heat capacity

Journal of Thermal Analysis and Calorimetry
Authors: D. Hourston, M. Song, H. Pollock, and A. Hammiche

Abstract  

Modulated-temperature differential scanning calorimetry was used to measure the glass transition temperature,T g, the heat capacity relaxation in the glassy state and the increment of heat capacity, δCp, in the glass transition region for several polymers. The differential of heat capacity with respect to temperature was used to analyseT g and δCp simply and accurately. These measurements are not affected by complex thermal histories.

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Introduction Differential scanning calorimetry (DSC) is extensively used in chemistry and physics to analyze, e.g. phase transitions of different compounds [ 1 , 2 ]. Recently this technique has been used with increasing

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Differential scanning calorimetry

A tool to assess physical and chemical alterations in liposomes

Journal of Thermal Analysis and Calorimetry
Authors: A. Samuni, D. Crommelin, N. Zuidam, and Y. Barenholz

Abstract  

This study was aimed to investigate the physicochemical changes induced in 200 nm extruded oligolamellar DPPC:DPPG (10:1) liposomes by freezing, followed by γ-irradiation, in the absence and presence of 5 mM stable cyclic nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol). The characterization is based on the use of differential scanning calorimetry (DSC) and was aimed to differentiate the contribution of freezing and γ-irradiation in the presence and absence of nitroxides. Liposomal preparations of DPPC/DPPG which have sub-, pre- and main-phase transitions in the temperature range (0�C<T m<50�C) were used. Our results show that: (1) freezing modified and induced fusion to MLV as well as fission to SUV, (2) freezing did not fully prevent the radiation-induced changes in the thermotropic characteristics of the liposomes, and (3) Tempo and Tempol did not prevent the changes in thermotropic behavior caused as a result of freezing of the liposomal dispersion. These results demonstrate that DSC is a powerful and sensitive tool in both physical and chemical studies of lipid assemblies.

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Multicycle differential scanning calorimetry

Thermophysical procedures for research, development, and quality control of substances and materials

Journal of Thermal Analysis and Calorimetry
Authors: E. Marti, E. Kaisersberger, and E. Füglein

Abstract  

Multicycle Differential Scanning Calorimetry (MCDSC) is a procedure where repeated temperature cycles are executed and the measured data are superimposed for a selected number of cycles. Temperature cycles with a single sample are executed under selected experimental conditions in one of these procedures, namely, the MCDSCs. The second one, MCDSCm is a procedure in which every identical temperature cycle starts with a new sample of the same substance of a similar mass. The procedure MCDSCs using the same sample for a number of cycles is only applicable for substances and materials which are chemically and physically stable under the selected experimental conditions. The application of MCDSC enhances two extremely important qualities of a DSC measurement, namely, the sensitivity and the statistical base, both qualities with respect to the final data elucidated. Another possibility by MCDSC also related to the enhanced sensitivity can lead the discovery of a phenomenon which hitherto has not been observed. The most important result of any MCDSC application is the determination of the mean DSC curve within the temperature interval of interest by superimposing the single curves point by point and by the division of the calorimetric values obtained with the number of scans evaluated. The signal-to-noise-ratio (SNR) for the mean curve can be compared with the value determined for one or even for all the single curves measured yielding the improvement factor achieved with a MCDSC measurement. This experimentally determined improvement of the SNR can be compared with the value given on a statistical consideration by Gauss as the square root of the number of cycles evaluated. The main aims of this article are to prove the practical application of the procedure and the efficiency in case of rather small sample masses. Substances were selected with known enthalpy transitions and, in addition, polystyrene was taken for a determination of the data for the glass transition by MCDSC. Rather small sample masses in the order of micrograms as well as the experimental conditions have been selected for the measurements with 4,4′-azoxyanisole and n-hexatriacontane with the expectation to get a value of SNR for the single curves of about unity or even below. Two aims should be achieved with these experiments. First, the multicycle procedures and the data evaluation developed should be capable of establishing, after performing of a certain number of cycles, a mean curve showing an improvement over the SNR with respect to the single curves. Second, we should be able to get a rough estimation of the lower limit of the SNR for a single curve, below the instrumental noise level of the DSC used, necessary to achieve with a MCDSC experiment a mean curve with a clearly visible peak.

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Modulated temperature differential scanning calorimetry

Characterization of curing systems by TTT and CHT diagrams

Journal of Thermal Analysis and Calorimetry
Authors: A. Van Hemelrijck and B. Van Mele

Abstract  

Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the (heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.

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Modulated temperature differential scanning calorimetry

Considerations for a quantitative study of thermosetting systems

Journal of Thermal Analysis and Calorimetry
Authors: G. Van Assche, A. Van Hemelrijck, and B. Van Mele

Abstract  

The influence of temperature modulation and signal treatment (deconvolution procedure) of modulated temperature differential scanning calorimetry is discussed with respect to the investigation of cure kinetics of thermosetting systems. The use of a ‘dynamic’ heat capacity calibration is not important for this purpose due to normalization of the heat capacity signal in all cure experiments. The heat flow phase during isothermal and non-isothermal cure is always small, giving rise to negligible corrections on the heat capacity and reversing heat flow signals in-phase with the modulated heating rate. The evolution of the heat flow phase contains information on relaxation phenomena in the course of the chemical reactions.

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]. J. Chiu P. G. Fair 1979 Determination of thermal conductivity by differential scanning calorimetry Thermochimica Acta

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Journal of Thermal Analysis and Calorimetry
Authors: Javier A. Díaz-Ponce, Eugenio A. Flores, Alfonso Lopez-Ortega, Jose G. Hernández-Cortez, Arquimides Estrada, Laura V. Castro, and Flavio Vazquez

methods, have been studied by thermogravimetrical analysis [ 4 , 5 ]. Similarly, differential scanning calorimetry (DSC) has shown to be a reliable method to elucidate some of the main features of the saturate, aromatic resins and asphaltenes constituting

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structure and thermal behavior including plasticization, gelatinization, and retrogradation is crucial. Differential scanning calorimetry (DSC) and hot-stage polarized optical microscopy are methods of choice for studying starch gelatinization. The

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Introduction Temperature-modulated differential scanning calorimetry (TMDSC) developed by Reading et al. [ 1 ] was commercialized shortly afterward and is being widely applied in different fields such as material research

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