Authors:M. Minohara, K. Tozaki, H. Hayashi, and H. Inaba
The melting transition of Ga and In was measured
by using a nW-stabilized differential scanning calorimeter working in a magnetic
bore. The magnetic effect on the thermometer was about 18 mK at 5 T, which
was corrected for the measurement of the magnetic effect on the melting transition
of Ga and In. The melting temperatures of Ga and In with the magnetic field
of 5 T were obtained to be 8.3 and 10.2 mK, respectively higher than those
without the magnetic field. These results show that the solid phase to be
relatively more stable under the magnetic field. The calculated temperature
shifts of the melting transition due to the magnetic field using the magneto-Clapeyron
equation and the reference data of magnetic susceptibility were negative values
for both Ga and In, being contradictory to the experimental results.
Authors:M. Pyda, Manika Varma-Nair, W. Chen, H. S. Aldrich, R. H. Schlosberg, and B. Wunderlich
Quantitative thermal analysis was carried out for tetra[methyleneoxycarbonyl(2,4,4-trimethyl)pentyl]methane. The ester has a glass transition temperature of 219 K and a melting temperature of 304 K. The heat of fusion is 51.3 kJ mol−1, and the increase in heat capacity at the glass transition is 250 J K−1 mol−1. The measured and calculated heat capacities of the solid and liquid states from 130 to 420 K are reported and a discussion of the glass and melting transitions is presented. The computation of the heat capacity made use of the Advanced Thermal Analysis System, ATHAS, using an approximate group-vibration spectrum and a Tarasov treatment of the skeletal vibrations. The experimental and calculated heat capacities of the solid ester were compared over the whole temperature range to detect changes in order and the presence of large-amplitude motion. An addition scheme for heat capacities of this and related esters was developed and used for the extrapolation of the heat capacity of the liquid state for this ester. The liquid heat capacity for the title ester is well represented by 691.1+1.668T [J K−1 mol−1]. A deficit in the entropy and enthalpy of fusion was observed relative to values estimated from empirical addition schemes, but no gradual disordering was noted outside the transition region. The final interpretation of this deficit of conformational entropy needs structure and mobility analysis by solid state13C NMR and X-ray diffraction. These analyses are reported in part II of this investigation.
Polymer molecules have contour lengths which may exceed the dimension of microphases. Especially in semicrystalline samples
a single molecule may traverse several phase areas, giving rise to structures in the nanometer region. While microphases have
properties that are dominated by surface effects, nanometer-size domains are dominated by interaction between opposing surfaces.
Calorimetry can identify such size effects by shifts in the phase-transition temperatures and shapes, as well as changes in
heat capacity. Specially restrictive phase structures exist in drawn fibers and in mesophase structures of polymers with alternating
rigid and flexible segments. On several samples shifts in glass and melting temperatures will be documented. The proof of
rigid amorphous sections at crystal interfaces will be given by comparison with structure analyses by X-ray diffraction and
detection of motion by solid state NMR. Finally, it will be pointed out that nanophases need special attention if they are
to be studied by thermal analysis since traditional ‘phase’ properties may not exist.
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.
Authors:W. Chen, A. Habenschuss, M. Pyda, Monika Varma-Nair, H. S. Aldrich, and B. Wunderlich
The symmetric neopolyol ester tetra[methyleneoxycarbonyl(2,4,4-trirnethyl)pentyl]methane (MOCPM) has been studied by variable-temperature solid-state13C NMR and X-ray powder diffraction and compared to molecular mechanics calculations of the molecular structure. Between melting and glass transition temperatures the material is semicrystalline, consisting of two conformationally and motionally distinguishable phases. The more mobile phase is liquid-like and is, thus attributed to an amorphous phase (≈16%). The branches of the molecules in the crystal exhibit two conformationally distinguishable behaviors. In one, the branches are well ordered (≈56%), in the other, the branches are conformationally disordered (≈28%). Different branches of the same molecule may show different conformational order. This unique character of the rigid phase is the reason for the deficit of the entropy of fusion observed earlier by DSC. In the melt, solid state NMR can identify two bonds that are rotationally immobile, even though the molecules as a whole have liquid-like mobility. This partial rigidity of the branches accounts quantitatively for the observed increase in heat capacity at the glass transition. The reason for this unique behavior of MOCPM, a small molecule, is the existence of one chiral centers in each of the four arms of the molecule. A statistical model assuming that at least two of the chiral centers must fit into the order of the crystal can explain the crystallization behavior and would require 12.5% amorphous phase, 28.1% conformational disorder, and 59.4% crystallinity, close to the observed maximum perfection.
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
Light heating dynamic DSC was used to study the melting transition of polyethylene. The results show that melting and crystallization
are different phenomena from each other in terms of the complex heat capacity. Frequency dependence of the complex heat capacity
was examined from 0.01 Hz to 0.2 Hz. It is found that at the lowest frequency the phase of the complex heat capacity exceeds
π/2 radians. Thermodynamic considerations were made for the large phase of the complex heat capacity.
DSC can be used to quickly determine if a product labeled as butter is actually a recombined butter made without milk. Recombined
butter is manufactured from anhydrous milk fat, skim milk powder, water, salt, and lecithin. Melting profiles of tempered
samples of natural butter and recombined butter were alike, but DSC curves from 5 to 25°C of untempered refrigerated samples
revealed that the enthalpy of the melting transition around 17–20°C was much higher for natural butter than for recombined
butter. The procedure for differentiating the two products can be completed in less than 20 min.
Authors:Natalia Avramenko, M. Korobov, Aksana Parfenova, P. Dorozhko, Natalia Kiseleva, and P. Dolgov
In an effort to improve
understanding of dissolution behaviour of fullerenes and their simple chemical
derivatives the binary systems of C60, C70
and the piperazine monoadduct of  fullerene C60
with a series of aromatic solvents have been studied by means of DSC. In certain
systems solid solvates have been found to be the thermodynamically stable
phases relative to saturated solution at room temperature. Identified solid
solvates were characterized by their compositions, temperatures and enthalpies
of incongruent melting transitions. The regularities in thermodynamic stability
of the solvated crystals have been discussed along with dissolution properties
of fullerenes and the derivative. Certain correlations have been observed.