Differential Scanning Calorimetry heat capacity

DSC (differential scanning calorimetry) Heat capacity versus temperature or time allows measurement of heats of fusion, identification of crystalline and liquid crystalline phases, degrees of crystallinity, etc. Glass transition measurement allows characterisation of ageing, blend compatibilities. Heats of reaction allow cure and degradation studies. 

In differential scanning calorimetry (DSC), higher precision can be obtained and heat capacities can be measured. The apparatus is similar to that for a DTA analysis, with the primary difference being that the sample and reference are in separate heat sinks that are heated by individual heaters (see the following illustration). The temperatures of the two samples are kept the same by differential heating. Even slight... 

A3 AIBN c Cp DLS DLVO DSC EO GMA HS-DSC KPS LCST Osmotic third virial coefficient 2,2 -Azobis(isobutyronitrile) Polymer concentration Partial heat capacity Dynamic light scattering Derjaguin-Landau-Verwey-Overbeek Differential scanning calorimetry Ethylene oxide Glycidylmethacrylate High-sensitivity differential scanning calorimetry Potassium persulphate Lower critical solution temperature... 

Fig. 2 Typical thermogram obtained using conventional differential scanning calorimetry on PNIPAM solution the temperature of maximum heat capacity (Tmax), the width of the transition at half-height (AT1/2), the heat of transition (AH), the difference in the heat capacity before and after the transition (ACp), and the demixing temperature (Tdem). (Adapted from Ref. [200])...

One such property, as has been demonstrated (see [26]), is the change in partial heat capacity of the copolymer solution upon the heat-induced conformational transition of macromolecules. Such a change was detected by high-sensitivity differential scanning calorimetry (HS-DCS). The DSC data for the NVCl/NVIAz-copolymers synthesized at initial comonomer ratios of 85 15 and 90 10 (mole/mole) are given as thermograms in Fig. 4. 

To use equation 2.10 correctly, we need to know how the heat capacities vary in the experimental temperature range. However, these data are not always available. A perusal of the chemical literature (see appendix B) will show that information on the temperature dependence of heat capacities is much more abundant for gases than for liquids and solids and can be easily obtained from statistical mechanics calculations or from empirical methods [11]. For substances in condensed states, the lack of experimental values, even at a single temperature, is common. In such cases, either laboratory measurements, using techniques such as differential scanning calorimetry (chapter 12) or empirical estimates may be required. 

Differential scanning calorimetry (DSC) was designed to obtain the enthalpy or the internal energy of those processes and also to measure temperature-dependent properties of substances, such as the heat capacity. This is done by monitoring the change of the difference between the heat flow rate or power to a sample (S) and to a reference material (R), A

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S. M. Sarge, W. Poe 3necker. Thelnfluence of Heat Resistances andHeat Transfers on the Uncertainty of Heat Capacity Measurements by Means of Differential Scanning Calorimetry. Thermochim. Acta 1999, 329, 17-21. 

Hemingway B. S., Krupka K. M., and Robie R. A. (1981). Heat capacities of the alkali feldspars between 350 and 1000 K from differential scanning calorimetry, the thermodynamic functions of alkali feldspars from 298.15 to 1400 K, and the reaction quartz + jadeite = albite. Amer. Mineral, 66 1202-1215. 

The measurement of the amount of heat released or absorbed in a reaction also included in this category are determinations of heat capacities, latent heats, and caloric values of fuels. See also Differential Scanning Calorimetry... 

Diedrich, A. and Gmehling, J., Measurement of heat capacities of ionic liquids by differential scanning calorimetry. Fluid Phase Equilib., 244, 68, 2006. 

Differential scanning calorimetry (DSC). The DSC analyses were carried out using a Perkin-Elmer DSC-7 and a DuPont 910DSC. Tg was defined as the midpoint of the change in heat capacity occurring over the transition. The samples were first scanned to 95°C, thereafter cooled and recorded a second time. The Tg was determined from the second run. The measurements were carried out under an atmosphere of dry nitrogen at a heating rate of 10°C/min. 

Differential scanning calorimetry is primarily used to determine changes in proteins as a function of temperature. The instrument used is a thermal analysis system, for example a Mettler DSC model 821e. The instrument coupled with a computer can quickly provide a thermal analysis of the protein solution and a control solution (no protein). The instrument contains two pans with separate heaters underneath each pan, one for the protein solution and one for the control solution that contains no protein. Each pan is heated at a predetermined equal rate. The pan with the protein will take more heat to keep the temperature of this pan increasing at the same rate of the control pan. The DSC instrument determines the amount of heat (energy) the sample pan heater has to put out to keep the rates equal. The computer graphs the temperature as a function of the difference in heat output from both pans. Through a series of equations, the heat capacity (Cp) can be determined (Freire 1995). 

Heat capacity is best determined with a calorimeter incorporating an electric heater. The net energy input and the resultant temperature rise are both measured. Procedures and precautions for such direct calorimetry are discussed thoroughly by Sturtevant (1959). Differential scanning calorimetry is convenient to use for the determination of heat capacity (Watson et al. 1964). 

Figure 17.1 Thermal unfolding of bamase measured by calorimetry and spectroscopy. The heat capacity of bamase (trace A) was measured using differential scanning calorimetry with a baseline (trace B) of buffer versus buffer Tm is 310.9 0.01 K, A D-N(cai) = 98.4 0.2kcal/mol, and A//D N(vh) = 98.1 0.3 kcal/mol. The ellipticity at 230 nm in the circular dichroism (trace C) under identical conditions fits Tm = 310.5 0.1 K, and A//D N(vh) = 93 3 kcal/mol (equation 17.5).

ASTM E1269, 2004. Standard test method for determining specific heat capacity by differential scanning calorimetry. 

In differential scanning calorimetry (DSC), quantitative results can be obtained and heat capacities can... 

High-pressure differential scanning calorimetry (Handa, 1986d Le Parlouer et al., 2004 Palermo et al., 2005) Yes P, T Yes Hydrate phase vs. time Typically up to 5800 psi, 230 to 400 K 7 isS, heat capacities, heat of dissociation. Emulsion stability and hydrate agglomeration... 

Differential scanning calorimetry (DSC) Since lc s form phases in a thermodynamic sense, a transition from one phase to another is accompanied by a phase-transition enthalpy. Nevertheless, there are phase transitions of second-order character which can hardly be detected by DSC since there is no phase-transition enthalpy but just a change in heat capacity. A typical example is the transition from orthogonal phases to tilted phases. 

A study of two of the most prominent and widespread osmolytes, betaine and beta-hydroxyectoine, by differential scanning calorimetry (DSC) on bovine ribonu-clease A (RNase A) revealed an increase in the melting temperature Tm of RNase A of more than 12 K and of protein stability AG of 10.6 kj mol-1 at room temperature at a 3 M concentration of beta-hydroxyectoine. The heat capacity difference ACp between the folded and unfolded state was significantly increased. In contrast, betaine stabilized RNase A only at concentrations less than 3 M. When enzymes are applied in the presence of denaturants or at high temperature, beta-hydroxyectoine should be an efficient stabilizer. 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

Similar to the DTA system noted above, differential scanning calorimetry (DSC) consists of a sample cell and reference cell, where platinum sensors detect the temperature in each cell. In the case of DSC, however, each cell possesses an individual heater (Figure 18.11B) so that energy input to the individual heaters is recorded as the instrument attempts to maintain equivalent temperatures in each cell while scanning a preset temperature range. The detector thus is able to directly measure the difference in heat capacity between the sample cell and the reference cell. 

This would not be problematic if standardized, reliable, reproducible, and inexpensive laboratory tests were available to estimate each of the required properties. Although several specialized laboratory tests are available to measure some properties (e.g., specific heat capacity can be determined by differential scanning calorimetry [DSC]), many of these tests are still research tools and standard procedures to develop material properties for fire modeling have not yet been developed. Even if standard procedures were available, it would likely be so expensive to conduct 5+ different specialized laboratory tests for each material so that practicing engineers would be unable to apply this approach to real-world projects in an economically viable way. Furthermore, there is no guarantee that properties measured independently from multiple laboratory tests will provide accurate predictions of pyrolysis behavior in a slab pyrolysis/combustion experiment such as the Cone Calorimeter or Fire Propagation Apparatus. 

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