A new pressure DSC module (Mettler DSC27HP) and its abilities for vapor pressure determination in the range of subambient
pressure to 7 MPa are presented. To compare the new to an established method, vapor pressures of caffeine, naphthalene and
o-phenacetin have been determined both by pressure DSC and the Knudsen effusion cell method. These results, including the
derived heats of evaporation and heats of sublimation, are compared to literature values.
The multiple melting peaks observed on differential scanning calorimetry (DSC) of ultrahigh molar-mass polyethylene fibers
(UHMMPE) are analyzed as a function of sample mass. Using modern DSC capable of recognizing single fibers of microgram size,
it is shown that the multiple peaks are in part or completely due to sample packing. Loosely packed fibers fill the entire
volume of the pan with rather large thermal resistance to heat flow. On melting, the fibers contract and flow to collect ultimately
at the bottom of the pan. This process seems to be able to cause an artifact of multistage melting dependent on the properties
of the fibers. A method is proposed to greatly reduce, or even eliminate, errors of this type. The crucial elements of the
analysis of melting behavior and melting temperature are decreasing the sample size and packing the individual fibers in a
proper geometry, or to introduce inert media to enhance heat transport.
The application of thermal analysis and other techniques to determine the thermal and mechanical history of an object is extended to investigate the method of manufacturing of ancient papers. The Humboldt Fragment number six of the Codex Huamantla and other Mexican papers are analyzed by means of Differential Scanning Calorimetry (DSC) and Thermogravimetry-Mass Spectroscopy (TG-MS). The results reveal mechanical treatment or beating of the raw material and also indicate, that the two cultures exchanged knowledge about the paper making. The simplicity and speed of thermoanalytical methods make them a good choice to screen samples for composition and origin. With the addition of more elaborate techniques, such as X-ray analysis, IR spectroscopy, evolved gas analysis by mass spectrometry and microscopy, a definitive classification can be reached easily.
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.
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
The mathematical equations for step-wise measurement of heat capacity (Cp) by modulated differential scanning calorimetry (MDSC) are discussed for the conditions of negligible temperature gradients
within sample and reference. Using a commercial MDSC, applications are evaluated and the limits explored. This new technique
permits the determination ofCp by keeping the sample continually close to equilibrium, a condition conventional DSC is unable to meet. Heat capacity is
measured at ‘practically isothermal condition’ (often changing not more than ±1 K). The method provides data with good precision.
The effects of sample mass, amplitude and frequency of temperature modulation were studied and methods for optimizing the
instrument are proposed. The correction for the differences in sample and reference heating rates, needed for high-precision
data by standard DSC, do not apply for this method.
Authors:A. Boller, I. Okazaki, K. Ishikiriyama, G. Zhang and B. Wunderlich
The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on the symmetry of the twin
calorimeters. This symmetry is of particular importance for the temperature-modulated DSC (TMDSC) since positive and negative
deviations from symmetry cannot be distinguished in the most popular analysis methods. Three different DSC instruments capable
of modulation have been calibrated for asymmetry using standard non-modulated measurements and a simple method is described
that avoids potentially large errors when using the reversing heat capacity as the measured quantity. It consists of overcompensating
the temperature-dependent asymmetry by increasing the mass of the sample pan.
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:A. Hensel, J. Dobbertin, J. E. K. Schawe, A. Boller and C. Schick
The results from temperature modulated DSC in the glass transition region of amorphous and semicrystalline polymers are described with the linear response approach. The real and the imaginary part of the complex heat capacity are discussed. The findings are compared with those of dielectric spectroscopy. The frequency dependent glass transition temperature can be fitted with a VFT-equation. The transition frequencies are decreased by 0.5 to 1 orders of magnitude compared to dielectric measurements. Cooling rates from standard DSC are transformed into frequencies. The glass transition temperatures are also approximated by the VFT-fit from the temperature modulated measurements. The differences in the shape of the curves from amorphous and semicrystalline samples are discussed.