Experiments using a commercial modulated DSC (MDSC) for the measurement of specific heat capacity of a sample have been carried
out. It is found that because the amplitude of heat flow of MDSC is a complicated non-linear function of various experimental
conditions such as the modulation frequency and the heat capacities of a sample and pan, the methodology of heat capacity
determination using an MDSC in a single run has not been justified. The experimental results, on the other hand, agree with
the theoretical equation of one of the authors. It is therefore concluded that the capabilities of MDSC should be further
Authors:Yimin Jin, J. Bonilla, Ye-Gang Lin, J. Morgan, Linda McCracken, and J. Carnahan
Two poly(butylene terephthalate)/polycarbonate (PBT/PC) blends with different formulations were analyzed by modulated DSC (MDSC) and conventional DSC to determine differences in crystallization behavior. A significant difference (30°C in cold crystallization temperature) between the two samples was detectable by MDSC while no significant difference was seen by conventional DSC. That indicatesthe total heat flow from MDSC is not always equivalent to the heat flow from conventional DSC as we have assumed or seen before. The reason has not been fully understood, but may be related to unusual nucleation and crystallization induced by modulation. Alternative conventional DSC methods were developed and compared to the MDSC results.
Authors:Z. Mohd Ishak, P. Shang, and J. Karger-Kocsis
The polymerization of a cyclic butylene terephthalate
(CBT) oligomer was studied as a function of temperature (T=200
and 260C, respectively) by modulated DSC (MDSC). The first heating was
followed by cooling after various holding times (5, 15 and 30 min) prior to
the second heating which ended always at T=260C.
This allowed us to study the crystallization and melting behavior of the resulting
polybutylene terephthalate (PBT), as well. In contrary to the usual belief,
the CBT polymerization is exothermic and the related process is superimposed
to that of the CBT melting. The melting behavior of the PBT was affected by
the polymerization mode (performed below or above the melting temperature
of the PBT product) of the CBT. Annealing above the melting temperature of
PBT yielded a product featuring double melting. This was attributed to the
presence of crystallites with different degrees of perfection. The crystals
perfection which occurred via recrystallization/remelting was manifested by
a pronounced exothermic peak in the non-reversing trace.
Authors:Y. Matsuda, C. Matsui, Y. Ike, M. Kodama, and S. Kojima
heat capacity, Cp*=Cp'–iCp'',
of lithium borate glasses xLi2O(1–x)B2O3
(molar fraction x=0.00–0.30) has
been investigated by Modulated DSC. We have analyzed the shape of Cp*
by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation,
and then determined the parameters related to the non-Debye nature of thermal
relaxation. Moreover, the concentration dependence of the thermal properties
has been investigated. Glass transition temperatures become higher with the
increase of molar fraction of Li2O and shows the board
peak around x=0.26. Temperature ranges
of glass transitions become narrower with the increase of Li2O
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:C. Giavarini, F. Maccioni, and Maria Santarelli
Modulated DSC has been applied to the study of methane,
ethane and propane hydrates at different hydrate and ice concentrations. The
reversing component of the TMDSC curves, makes it possible to characterize
Methane and ethane hydrates show the melting-decomposition
peak at a temperatures higher than the ice contained in the sample, while
propane hydrate melts and decomposes at lower temperature than the ice present
in the sample. The hydrate peaks tend to disappear if the hydrate is stored
at atmospheric pressure. Guest size and cavity occupation fix the heat of
dissociation and stability of the hydrates, as confirmed by parallel tests
on tetrahydrofurane hydrates.
Authors:Iria Fraga, S. Montserrat, and J. Hutchinson
TOPEM is a new temperature modulated DSC technique, introduced by Mettler-Toledo
in late 2005, in which stochastic temperature modulations are superimposed
on the underlying rate of a conventional DSC scan. These modulations consist
of temperature pulses, of fixed magnitude and alternating sign, with random
durations within limits specified by the user. The resulting heat flow signal
is analysed by a parameter estimation method which yields a so-called ‘quasi-static’
specific heat capacity and a ‘dynamic’ specific heat capacity
over a range of frequencies. In a single scan it is thus possible to distinguish
frequency-dependent phenomena from frequency-independent phenomena. Its application
to the glass transition is examined here.
The static loading-induced stress oscillation (SO) in syndiotactic polypropylene (sPP) was studied by modulated differential scanning calorimetry (TMDSC). Samples were taken from the initial necked, premature and mature SO oscillation ranges, respectively, and the related calorimetric responses were compared to those of the bulk material. It was established that necking caused some decrease in the crystallinity. In addition, necking resulted in cold crystallization that was assigned to a polymorphic transition (from all-trans to helical conformation) based on literature results. The TMDSC response was practically the same for necked samples with and without SO. A model was proposed to explain SO. The model assumes the presence of a network (similar to that of semicrystalline thermoplastic elastomers), which is highly stretchable and fails by sudden voiding at the intersections of shear micro bands intermittently.
A new type of the light modulated DSC was constructed. Optical fibers are used to separate the light source from the furnace.
The sample can be handled accurately because the lamp and the intensity modulator are not above the furnace. Quality of the
measured signal is much improved by extracting the analog signal from the electronic circuit board in the commercial DSC.
Light intensities of the sample and reference sides are controlled independently from each other. A method to compensate for
the asymmetry of the thermal system utilizing the independent control of the light intensity is proposed.
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.