Modulated differential scanning calorimetry

Modulated DSC^TM (MDSC) is a new, patent-pending extension to conventional DSC which provides information about the reversing and nonreversing characteristics of thermal events, as well as the ability to directly measure heat capacity. This additional information aids interpretation and allows unique insights into the structure and behaviour of materials., A number of examples of its use are described.     

Modulated differential scanning calorimetry

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, C_p, in the glass transition region for several polymers. The differential of heat capacity with respect to temperature was used to analyseT _g and C_p simply and accurately. These measurements are not affected by complex thermal histories.     

Modulated differential scanning calorimetry

The Modulated Differential Calorimetry (MDSC) is applied to the determination of the reversibility in the cholesteryl chloride, which presents a cholesteric monotropic phase between the isotropic and crystalline states. The experimental modulation parameters that govern this method i.e. frequency, amplitude and heating/cooling rate, are determined. MDSC curves and complementary thermomicroscopical observations assign melting, crystallization and liquid cholesteric transition as non reversing, and clarification as reversing.     

Modulated differential scanning calorimetry in the glass transition region

Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate) (PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be used to match model and experiment.On leave from Toray Industries, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy, under contract number DE-AC05-96OR22464. Support for instrumentation came from TA Instruments, Inc. Research support was also given by ICI Paints, and Toray Industries, Inc.     

Modulated differential scanning calorimetry in the glass transition region

Temperature-modulated differential scanning calorimetry (TMDSC) is based on heat flow and represents a linear system for the measurement of heat capacity. As long as the measurements are carried out close to steady state and only a negligible temperature gradient exists within the sample, quantitative data can be gathered as a function of modulation frequency. Applied to the glass transition, such measurements permit the determination the kinetic parameters of the material. Based on either the hole theory of liquids or irreversible thermodynamics, the necessary equations are derived to describe the apparent heat capacity as a function of frequency.Presented in part at the 24th Conference of the Northamerican Thermal Analysis Society, San Francisco, CA, September 10–13, 1995.     

Cell asymmetry correction for temperature modulated differential scanning calorimetry

The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on strict symmetry of the twin calorimeter. This symmetry is of particular importance for temperature-modulated DSC (TMDSC) since positive and negative deviations from symmetry cannot be distinguished in the most popular analysis methods. The heat capacities for sapphire-filled and empty aluminum calorimeters (pans) under designed cell imbalance caused by different pan-masses were measured. In addition, the positive and negative signs of asymmetry have been explored by analyzing the phase-shift between temperature and heat flow for sapphire and empty runs. The phase shifts change by more than 180° depending on the sign of the asymmetry. Once the sign of asymmetry is determined, the asymmetry correction for temperature-modulated DSC can be made.On leave from Toray Research Center, Inc., Otsu, Shiga 520, JapanThis work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy, under contract number DE-AC05-960R22464.     

Multicycle differential scanning calorimetry

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 MCDSC_s. The second one, MCDSC_m is a procedure in which every identical temperature cycle starts with a new sample of the same substance of a similar mass. The procedure MCDSC_s 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.     

Determination of ultra-low glass transition temperature via differential scanning calorimetry

A novel method was developed to determine the ultra-low glass transition temperature (T_g) of materials through physical blending via differential scanning calorimetry. According to the Fox equation for polymer blends, a blend of two fully compatible polymers has only one T_g. The single T_g is a function of the T_gs of the two simple polymers. Thus, the ultra-low T_g of one material can be obtained from the T_gs of another polymer and their blends. The error of T_g measurements depends on the measurement error of the T_gs for the blends and another polymer. The method was successfully applied to determine the T_gs of acetyl tributyl citrate (ATBC), tributyl citrate (TBC) and poly(ethylene glycol)s (PEG)s with different molecular weights. The T_gs for ATBC, TBC, PEG-4000 and PEG-800 were ?57.0 °C, ?62.7 °C, ?76.6 °C and ?83.1 °C, respectively. For all the samples, the standard deviation of measurements was less than 3.3 °C, and the absolute error of measurements was theoretically not more than 5.3 °C. These results indicate that this method has acceptable precision and accuracy.     

Temperatures in differential scanning calorimetry

A recently described method is used to characterise thermal gradients in a DSC-2 and the results are compared with a conventional temperature calibration. Under certain circumstances the latter may be in error by several degrees with consequent adverse effects on calculated heat capacities. The errors are removed when allowance is made for variations in thermal lag from sample to sample.     

Simplification of differential temperature calibration and emittance measurements in scanning calorimetry

The energy emitted by the two sample holders of a Perkin—Elmer Differential Scanning Calorimeter (DSC) can be balanced quickly at any temperature by observing instrument signal as a function of differential temperature control setting. This balance point, depending on the emittance characteristics of the individual sample holders, will correspond closely to the point at which the temperatures of the two sample holders are the same, making rapid differential temperature calibration possible. Deterioration in the characteristics of the sample holders can be detected, and emittance measurements can be greatly simplified.     

A study of gamma-irradiated polyethylenes by temperature modulated differential scanning calorimetry

Various polyethylenes (PEs) and the effects of high-energy radiation on their structures were widely studied in the past using conventional Differential Scanning Calorimetry (DSC) measurements. In this work, we used the Temperature Modulated Differential Scanning Calorimetry (TMDSC) technique in order to obtain more information about the influence of the initial structural differences and gamma radiation on the evolution in structure and thermal properties of different polyethylenes. For this reason, low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) samples were exposed to gamma radiation, in air, to a wide range of absorbed doses (up to 2400 kGy). The separation of the total heat flow TMDSC signal into a reversing and non-reversing part enabled us to observe the low-temperature enthalpy relaxation (related to the existence of the “rigid amorphous phase”) and recrystallisation processes, as well as to follow their radiation-induced evolution and/or that of melting in a more revealing manner compared to the case of the conventional DSC. Consequently, our results indicate that TMDSC could improve the understanding of radiation-induced effects in polymers.     

Thermal gradients in differential scanning calorimetry

A combined static and dynamic temperature calibration is described. The static calibration corrects the instrumental dial temperature reading. The dynamic calibration has instrumental and material components and therefore varies from specimen to specimen. It is obtained from individual DSC curves and so removes uncertainties in sample temperature due to varying mass, geometry, and heating rate. The instrumental performance is improved and specific heats may be obtained to an accuracy of ±1%.     

Quantitative aspects of differential scanning calorimetry

The quantitative performance of differential scanning calorimeters is reviewed. Temperature calibration is discussed in terms of an isothermal correction plus a contribution from thermal lag, this can be derived from individual curves and is valid in both, heating and cooling. It is emphasised that baselines that are drawn to thermal events, such as melting and transition phenomena, must have thermodynamic significance and a general procedure is suggested. When this is used, a power compensation calorimeter calibrated for heat-capacity work can reproduce heats of fusion and transition for a diverse range of materials to better than 1%.     

Use of cyclic differential scanning calorimetry

Formation of an activated cellulose (Cellulose) species $$CELLULOSE\xrightarrow[{air}]{{heat}}CELLULOSE*$$ is the designated first stage of cellulose degradation in air [1]. Little is known about either the process or the nature of CELLULOSE^*. The transition, designatedT ₂, is observed as an exotherm around 300°C as the sample temperature is raised. No corresponding endotherm is observed on cooling. The process is therefore not reversible but is repeatable as subsequent reheating results in the exotherm being observed again. The exotherm is also found to be oxygen dependant. The effect of all the flame retardant treatments studied was to reduceT ₂ compared to the value for the untreated cotton.     

Purity determination by differential scanning calorimetry

A review of the literature on the DSC method for purity determination is presented, with a discussion of the most important aspects, i.e. theory, sample handling, calibration of the instrument, evaluation of melting curves, and the conditions and accuracy of the measurement of eutectic impurities.     

The application of low temperature differential scanning calorimetry to polymer blend analysis

The temperature regions in which glass transitions (Tg's) occur for a series of blends of polybutadienes with natural rubber and two styrenebutadiene copolymers of different styrene contents have been studied by differential scanning calorimetry. The resulting DSC curves may be used to categorize the polybutadiene, determine the bound styrene content of the styrenebutadiene copolymer and quantify the polybutadiene content of the blends.

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Zusammenfassung Die Temperaturbereiche, in denen bei einer Reihe von Gemischen von Butadien mit natürlichem Kautschuk und bei zwei Styrol-Butadien-Kopolymeren mit verschiedenem Styrolgehalt Glastransformationen erfolgen, wurden mittels DSC untersucht. Die erhaltenen DSC-Kurven können zur Kategorisierung des Polybutadiens und zur Bestimmung des Gehalts an gebundenem Styrol in Styrol-Polybutadien-Kopolymeren und des Polybutadiengehalts der Gemische verwendet werden.

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Thanks are due to the Board of MRPRA for permission to publish this paper.     

Network formation studied by temperature scanning brillouin scattering and differential scanning calorimetry techniques. II.

The reaction of 1,4‐butanediol diglycidyl ether (EP) with cis‐1,2‐cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) as an initiator was studied with temperature scanning Brillouin spectroscopy (TSBS) and differential scanning calorimetry (DSC). The evolution of the reaction process (liquid–gel–solid) was investigated as a function of the epoxy molar fraction (x_EP), for sample compositions varying from an epoxy excess to an anhydride excess. The dependence of the final conversion factors αr_DSC and αr_TSBS and the kinetic parameters E_DSC and E_TSBS on x_EP is presented. A comparison of the experimental gelation point (Pgel) behavior and the expected theoretical one, described by the Flory theory, is also reported. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1326–1336, 2001     

Determination of elemental sulfur in phosphorous pentasulfide by temperature modulated differential scanning calorimetry

Phosphorous pentasulfide is an important starting material for a number of commercial chemicals. Examples include lubricant additives (Spikes, Trib Lett 17:469?C489, 2004), agricultural insecticides (Kirk-Othmer, Enycl Chem Technol 14:549?C552, 1995), and mining ore flotation agents. Phosphorous pentasulfide is a mixture of several components, one of which is free elemental sulfur, present at levels of approximately 50?ppm to 20,000?ppm (2?%). The amount of free sulfur present in the phosphorous pentasulfide can impact manufacturing, such as zinc dithiosulfate processing. Therefore, an accurate and fast analytical method to measure elemental sulfur in phosphorous pentasulfide would be of value compared to what is available now.