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(viscosity-average molar mass, M v = 300,000 g mol −1 ) and poly( d , l -lactide) (number-average molar mass M n = 43,000 g mol −1 ) show on DSC traces two separate glass transition temperatures ( T g ) independently of the composition, indicating thus
Abstract
The DSC method was used to study phase transitions in Rhododendron L. leaf tissues caused by temperatures below the freezing point of water. The curves show several stages of water crystallisation, demonstrating that these processes do not occur simultaneously in various types of cell organelles. Temperatures and enthalpies of the phase transitions were determined and significant changes were found in the DSC curves when the sample was repeatedly subjected to sub-zero temperature cooling and heating. Also, frost resistance of the same rhododendron taxons was studied by conductometric analysis and the DSC results were compared with the data from other laboratory studies.
. Recent literature screening shows the high interest in the use of thermoanalytical techniques, differential scanning calorimetry (DSC) and thermogravimetry (TG) for this purpose [ 4 – 6 ], as well as of spectroscopic techniques, IR spectroscopy with
Abstract
Differential scanning calorimetry (DSC) has been scarcely used in conservation field and in particular, in the study of painting layers. However DSC is a micro-destructive technique (sample from .05 to 1 mg can be analysed) because no pre-treatment of the sample is required and so it can give rapid and useful information. The aim of the present work is, in fact, to describe useful applications of DSC on the study of materials used in art. The analyses have been conducted under oxygen flow in order to register the thermo-oxidative reactions of the organic binder or protective. In the first part of the paper, materials of different chemical composition have been analysed to build up a data base of DSC profiles. Standard painting layers artificially degraded by treatment with ultraviolet light (365 nm) for 21 days and with NOx (5 ppm)have be en analysed. Comparing the behaviour of the treated to the reference sample, it is useful to study what kind of changes the treatments have produced on the sample. Another possible application of DSC is the study of the formation of the film; analysing the raw,liquid binders and the different naturally aged films an evolution of the chemical structure canbe registered. As a conclusion, DSC analyses on standard used in artistic field allow to investigate their thermal behaviour and to understand the effect of natural and artificial ageing.
Abstract
The application of non-linear heating program to a heat-flux DSC apparatus has attracted much attention. From thermodynamics viewpoint, it is shown that the variation of enthalpy of a sample changing with temperature change is due, to both the true heat capacity of the sample and the enthalpy of some transformations occurring in the sample, characterized by its degree of advance. Using the simple assumption that the rate of the transformation is proportional to the distance from the thermodynamic equilibrium, an electrical model of the thermal event is given. Using the coupled cell model of the DSC apparatus, we show how to obtain the rate of transformation of the sample and heat capacity, which is directly related to the base line of the experiment.
TOPEM, a new temperature modulated DSC technique
Application to the glass transition of polymers
Abstract
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.
Abstract
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.
curing dynamics of powder coatings, DSC is used as the common methods to obtain the kinetics of curing actions [ 5 – 8 ]. Furthermore, a novel and powerful FT-IR spectroscopy equipped with a heating cell has been used to simultaneously investigate the
Abstract
Symmetrical block oligomers having in common terminal groups (A) consisting of polyoxyethylene (20) stearyl ether are materials of pharmaceutical and cosmetic interest. Phase properties of their aqueous systems and amounts of water typologies were determined by differential scanning calorimetry (DSC). The overall amount of water absorbed by each investigated oligomer was not significantly influenced by the type of central bridging block, whereas the amount of free water decreased with increasing oligomer concentration in the gel. A number of 60–70 moles of water was found to solvate the oligomer chain. The oligomers studied presented a thermo-reversible gelation with and precipitation under determined temperature conditions.
Abstract
The melting of PbBr2 in sealed crucibles was investigated by means of DSC. Three factors were considered to affect melting point: i) impurities, ii) the bromine pressure over the PbBr2, and iii) photolysis. Both crystals and powders were investigated. The peak of the melting changed after sample grinding. The bromine pressure over the PbBr2 was found to cause a significant error in the determination of the melting point.Lead bromide melts at 370.6±0.2°C. The heat of melting is 42.9±1.8 J g–1.
