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 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.     

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.     

Temperature modulated differential scanning calorimetry (TMDSC) in the region of phase transitions. Part 1: theoretical considerations

For temperature modulated differential scanning calorimetry (TMDSC) a simple model, the low pass filter, is presented which allows to see and calculate the influence of heat transfer into the sample on magnitude and phase shift of the modulated part of the measured heat flow rate and the heat capacity determined from it. A formula is given which enables to correct the measured magnitude of the periodic heat flow rate function and the calculated heat capacity in dependence on the thermal resistance and heat capacity of the sample. The correction becomes very important in regions where the heat capacity changes considerably as in the melting region. The approach is successfully tested with model substances with well-known excess heat capacity in the transition region.     

Specific heat capacities of pure triglycerides by heat-flux differential scanning calorimetry

The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min^?1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level.     

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.     

Temperature Modulated DSC for the Investigation of Polymer Materials: A brief account of recent studies

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.     

Glass transition temperature of thin polycarbonate films measured by flash differential scanning calorimetry

Flash differential scanning calorimetry was used to study the glass transition temperature T_g of polycarbonate ultrathin films. The investigation was made as a function of film thickness from 22 to 350 nm and over a range of cooling rates from 0.1 to 1000 K/s. Polycarbonate spin cast films were floated on a layer of grease on the calorimetric chip. The results show a greatly reduced glass temperature for the thinnest films relative to the macroscopic value. We also observed that the magnitude of the glass temperature reduction decreases as the cooling rate increases with the highest cooling rates showing little thickness dependence of the T_g. Dynamic fragility and activation energy at T_g were found to decrease with decreasing film thickness. The results are discussed in the context of literature reports for supported and freely standing polycarbonate films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1462–1468     

Modulated temperature differential scanning calorimetry

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.     

Isothermal crystallization of concentrated amorphous starch systems measured by modulated differential scanning calorimetry

The slow isothermal crystallization of concentrated amorphous starch systems is measured by Modulated Differential Scanning Calorimetry (MDSC). It can be followed continuously by the evolution (stepwise decrease) of the MDSC heat capacity signal (Cp), as confirmed with data from X-ray diffractometry, Dynamic Mechanical Analysis, Raman spectroscopy, and conventional Differential Scanning Calorimetry. Isothermal MDSC measurements enable a systematic study of the slow crystallization process of a concentrated starch system, such as a pregelatinized waxy corn starch with 24 wt % water and 76 wt % starch. After isothermal crystallization, a broad melting endotherm with a bimodal distribution is observed, starting about 10°C beyond the crystallization temperature. The bulk glass transition temperature (T_g) decreases about 15°C during crystallization. The isothermal crystallization rate goes through a maximum as a function of crystallization time. The maximum rate is characterized by the time at the local extreme in the derivative of Cp (t_max), or by the time to reach half the decrease in Cp (t_1/2). Both t_max and t_1/2 show a bell-shaped curve as a function of crystallization temperature. The temperature of maximum crystallization rate, for the system studied, lies as high as 75°C. This is approximately 65°C above the initial value of T_g. Normalized Cp curves indicate the temperature dependence of the starch crystallization mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2881–2892, 1999     

Modulated Differential Scanning Calorimetry Observation of Physical Ageing in Polymers

Modulated-temperature differential scanning calorimetry (M-TDSC) is becoming a useful tool in the characterisation of thermal behaviour of polymers. In this paper, we discuss whether the non-reversing M-TDSC signal can be used, quantitatively and directly, to study the process of physical ageing in polymers. Difference exists between the values of relaxation enthalpy determined by using average heat capacity, <C _p>, signal as for conventional DSC and non-reversing heat capacity, C ⁿ _p, signal. When the signal of reversing heat capacity of unaged sample is considered as baseline for <C _p> and C ⁿ _p signals, the difference disappears. It is concluded that non-reversing M-TDSC signal can be used to observe the process of physical ageing semi-qualitatively and directly. With increasing annealing time, the peak of the imaginary part, C″_p, of the complex heat capacity becomes narrow, but peak area changes little. This indicated that C″_p is not correlated with relaxation enthalpy. It may be related to entropy change during the modulation. However, the entropy change is quite small. This revised version was published online in August 2006 with corrections to the Cover Date.     

Learning about calorimetry

Calorimetry deals with the energetics of atoms, molecules, and phases and can be used to gather experimental details about one of the two roots of our knowledge about matter. The other root is structural science. Both are understood from the microscopic to the macroscopic scale, but the effort to learn about calorimetry has lagged behind structural science. Although equilibrium thermodynamics is well known, one has learned in the past little about metastable and unstable states. Similarly, Dalton made early progress to describe phases as aggregates of molecules. The existence of macromolecules that consist of as many atoms as are needed to establish a phase have led, however, to confusion between colloids (collections of microphases) and macromolecules which may participate in several micro- or nanophases. This fact that macromolecules can be as large or larger than phases was first established by Staudinger as late as 1920. Both fields, calorimetry and macromolecular science, found many solutions for the understanding of metastable and unstable states. The learning of modern solutions to the problems of materials characterization by calorimetry is the topic of this paper.This work was financially supported by the Div. of Materials Res., NSF, Polymers Program, Grant # DMR 90-00520 and 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.     

The application of modulated differential scanning calorimetry to the glass transition

The modulated differential scanning calorimetry (MDSC) technique superimposes upon the conventional DSC heating rate a sinusoidally varying modulation. The result of this modulation of the heating rate is a periodically varying heat flow, which can be analysed in various ways. In particular, MDSC yields two components (reversing and non reversing) of the heat flow, and a phase angle. These each show a characteristic behaviour in the glass transition region, but their interpretation has hitherto been unclear. The present work clarifies this situation by a theoretical analysis of the technique of MDSC, which introduces a kinetic response of the glass in the transition region. This analysis is able to describe all the usual features observed by MDSC in the glass transition region. In addition, the model is also able to predict the effects of the modulation variables, and some of these are discussed briefly.Financial support has been provided by the DGICYT (Project no.PB93/1241). J.M.H. wishes to acknowledge financial assistance for a sabbatical period from the Generalitat de Catalunya.     

Modeling the heat flow and heat capacity of modulated differential scanning calorimetry

Modulated differential scanning calorimetry (MDSC) uses an abbreviated Fourier transformation ?r the data analysis and separation of the reversing component of the heat flow and temperature signals. In this paper a simple spread-sheet analysis will be presented that can be used to better understand and explore the effects observed in MDSC and their link to actual changes in the instrument and sample. The analysis assumes that instrument lags and other kinetic effects are either avoided or corrected for.     

Isothermal differential scanning calorimetry study of a glass/epoxy prepreg

Isothermal differential scanning calorimetry (DSC) was used to study the curing behavior of epoxy prepreg Hexply®1454 system, based on diglycidyl ether of bisphenol A (DEGBA)/dicyandiamid (DICY) reinforced by glass fiber. Cure kinetics of an autocatalytic‐type reaction were analyzed by general form of conversion‐dependent function. The characteristic feature of conversion‐dependent function was determined using a reduced‐plot method where the temperature‐dependent reaction rate constant was analytically separated from the isothermal data. An autocatalytic kinetic model was used; it can predict the overall kinetic behavior in the whole studied cure temperature range (115–130°C). The activation energy and pre‐exponential factor were determined as: E = 94.8 kJ/mol and A = 1.75 × 10¹⁰ sec^?1 and reaction order as 2.11 (m + n = 0.65 + 1.46 = 2.11). A kinetic model based on these values was developed by which the prediction is in good agreement with experimental values. Copyright © 2009 John Wiley & Sons, Ltd.     

A Theoretical Approach to Temperature Modulated Power Compensation DSC

The steady state of temperature modulated power compensation DSC has been theoretically investigated for measurements of complex heat capacity, taking accounts of heat capacities of heat paths, heat loss to the environment, and mutual heat exchange between the sample and the reference material. Thermal contact between the sample cell and the cell holder is also taken into accounts. Rigorous and general solutions are obtained. From these solutions application of the technique to heat capacity measurements is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of interfacial region of microphase-separated SEBS using modulated differential scanning calorimetry and dynamic mechanical thermal analysis

The continuous structural changes of Poly(styrene-b-ethylene-butylene-b-styrene) [SEBS] due to the effect of temperature are hard to evaluate using conventional differential scanning calorimetry (DSC). This paper presents an accurate and simple way to evaluate microstructural and glass transitions of SEBS using modulated differential scanning calorimetry (MDSC). The weak crystalline nature of –(CH₂-CH₂)–_n in the ethylene-butylene (EB) block melted around 36 °C. The premature molecular moment and Tg of the styrene block were at 62 °C and 96 °C, respectively. The interfacial region at high temperature was explained with respect to order-order transition (OOT) at 144 °C and a prominent Order-Disorder Transition (ODT) at around 202 °C. Dynamic mechanical thermal analysis (DMTA) and dynamic mechanical rheological testing (DMRT) measurements also revealed that the T_g of the PS transition were consistent at around 96 °C.     

Measurements of specific heat of meta-nitrobenzoic acid diethanolamine crystals—By differential scanning calorimetry

The specific heat capacity of M·NBA·DEA crystals were measured by differential scanning calorimetry. Both the direct and ratio methods of DSC were used in the determinations. The relative average deviations are 0.08% to 0.18%. The relative average deviations of ratio method are 0.23–0.69%.     

Improved conditions for measurement of the specific heat capacities of pure triglycerides by differential scanning calorimetry

Reproducible specific heat capacities (C _p) of triglycerides can be obtained by using heat-flux DSC under improved operating conditions. The improved operating parameters, such as the scanning rate, the sample mass and the atmosphere within the DSC chamber, were established via statistical analysis of the experimental data with trilaurin as a sample. The specific heat capacity results on trilaurin were compared with the values calculated by using estimation methods. The precision of the specific heat capacity measured for trilaurin under these conditions was within ±1%.