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-modulateddifferentialscanningcalorimetry (TMDSC) developed by Reading et al. [ 1 ] was commercialized shortly afterward and is being widely applied in different fields such as material research
Reading and co-workers introduced a new technique a few years ago called Modulated Differential Scanning Calorimetry or MDSC.
Here the first part of a theoretical analysis for this technique is given. A simple mathematical model for modulated differential
scanning calorimetry in the form of an ordinary differential equation is derived. The model is analysed to find the effect
of a kinetic event in the form of a chemical reaction. Some possible sources of error are discussed. A more sophisticated
version of the model allowing for spatial variation in a calorimeter is developed and it is seen how it can be reduced to
the earlier model. Some preliminary work on a phase change is also presented.
Authors:B. Wunderlich, A. Boller, I. Okazaki, and S. Kreitmeier
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.
Authors:K. Ishikiriyama, A. Boller, and B. Wunderlich
The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated
differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization
of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally
with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures
of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied.
For TMDSC with an underlying heating rate of 0.2 K min−1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within
0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of
steady state between sample and sensor on the one hand and from supercooling on the other.
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.
The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, Tg, (Tg-10C and Tg-20C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential
scanning calorimetry (MDSC). The experimentally measured instrumental Tg, the calculated Tg, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy
as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan
models. The change in the Tg values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed.
Authors:S. Aubuchon, L. Thomas, W. Theuerl, and H. Renner
40% w/w sucrose/water solutions were analyzed by Modulated Differential Scanning Calorimetry  in the sub-ambient temperature region. At these temperatures, the solutions exhibit a complex, two-step thermal event. The lower-temperature event is believed to be the glass transition of the amorphous sucrose phase. The nature of the higher-temperature event is the subject of controversy. This event has been shown to have distinct second-order characteristics, and as such is believed to be a second Tg. Others feel that this event is the onset of melting. The temperature region between these events contains a devitrification exotherm. Through the use of MDSC, both in scanning and stepwise quasi-isothermal modes, improved sensitivity and resolution of MDSC provides new insight into the nature of these transitions.
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.