Differential scanning calorimetry measurements Modulated

DTA (Differential Thermal Analysis) and DSG (Differential Scanning Calorimetry) measure the thermal transitions in materials by monitoring temperatures and heat flows. DTA is qualitative while DSC is quantitative. Glass transition temperatures, phase changes, heat capacity, cure kinetics and thermal degradation can be monitored by these techniques. Modulated DSC can be both faster and more accurate. 

Differential scanning calorimetry (DSC) compares the two different heat flows one to or from the sample to be studied, and the other to or from a substance with no phase transitions in the range to be measured, e.g. glassmaking sand. Figures 1.45.1 and 1.45.2 show artist s views of parts of a modulated DSC system, and Figure 1.46 shows a commercial apparatus for DSC measurements. 

Schawe, J. E. K. (1998). A description of the glass transition measured by temperature modulated differential scanning calorimetry. Colloid Polym. Sci. 276(7), 565-569. 

Pyda, M. Kwon, Y.K. Wunderlich, B. Heat capacity measurements by saw-tooth modulated standard heat-flux differential scanning calorimetry with sample temperature control. Thermochim. Acta 2001, 367 (8), 217-227. 

The book opens with the first three chapters devoted to differential scanning calorimetry (DSC), the most commonly used thermal method. These chapters cover the principles, optimal use, and pharmaceutical applications of the method. Subsequent chapters explore modulated temperature DSC, thermogravimetric analysis, thermal microscopy, microcalorimetry, high sensitivity DSC, dynamic mechanical analysis, and thermally stimulated current, all of which have attracted great interest within the pharmaceutical field. Each chapter includes theoretical background, measurement optimization, and pharmaceutical applications. 

As an independent experiment to verify the findings of the TDBS we also performed quasi adiabatic measurements of the specific heat capacity Cp (74) using modulated differential scanning calorimetry (N SC) (20-22). Usually the glass transition is characterized by a step like behavior of Cp(T). The thermal glass transition... 

The latest development (1992) is the Modulated Differential Scanning Calorimetry (MDSC). Here the linear heating rate is superimposed by a sinoidal modulation. The following advantages of this mode are claimed direct measurement of heat capacity improved resolution of adjacent or superimposed effects improved sensitivity for weak transition effects separation of reversible from irreversible effects... 

Pyda et al. (1998) studied in detail the heat capacity of PTT by adiabatic calorimetry, standard DSC and temperature-modulated differential scanning calorimetry (TMDSC) for this measurement. The computation of the heat capacity of solid PTT is based on an approximate group vibrational spectrum and the general Tarasov approach for the skeletal vibrations, using the well-established Advanced Thermal Analysis System (ATHAS) scheme. The experimental heat capacity at constant pressure is first converted to heat capacity at constant volume using the Nemst-Lindemann approximation... 

This concludes the discussion of thermometry and dilatometry. The tools to measure temperature, length, and volume have now been analyzed. The tools for measurement of heat, the central theme of this book, will take the next three sections and deal with calorimetry, differential scanning calorimetry, and temperature-modulated calorimetry. The mechanical properties which involve dilatometry of systems exposed to different and changing forces, ate summarized in Sect. 4.5. The measurement of the final basic variable of state, mass, is treated in Sect. 4.6 which deals with thermogravimetry. 

Calorimetry involves the measurement of the extensive quantity heat. Its name derives from the middle of the 18 century when heat was called the caloric, as described in Sects. 1.1.1 and 2.1.1. As the main thermal-analysis method, calorimetry is discussed in this and the following two sections, covering classical calorimetry in Sect. 4.2, differential scanning calorimetry (DSC) in Sect. 4.3, and the more recent temperature-modulated calorimetry (TMC) in Sect. 4.4. 

Calorimetric studies have depicted the impact of nanoparticles on isothermal curing of epoxy-amine system. Isothermal measurements done at 298 K using temperature-modulated differential scanning calorimetry are shown in Figure 9.15. The heat flow signal recorded during this measurement is directly proportional to the reaction rate of the curing process. It was foxmd that,... 

In addition to thermal conductivity, modifications of the sthm can yield thermal capacity or more specifically differential scanning calorimetry (dsc). Instead of heating the resistive wire with a constant power, its temperature is modulated with an ac current. The resultant amplitude and phase shift of the wire s temperature is measured with a lock-in-ampIifier. Simultaneously, the temperature of the tip and sample are ramped up slowly so as to measure the change in heat dissipation per change in temperatme, dq/dT. This measure is, of course, related to the local heat capacity of the sample and is correlated with expected phase... 

The sample (or furnace) temperature is controlled to follow a set course with superimposed periodical changes, and the heat flow rate is measured via the differential temperature between sample and reference (temperature-modulated differential scanning calorimetry, TMDSC [38]). 

Reading, M., Price, D. M., and Orliac, H. (2001), Measurement of crystallinity in polymer using modulated temperature differential scanning calorimetry, in Material Characterization by Dynamic and Modulated Thermal Analysis Techniques, American Society for Testing and Materials, Riga, A. T. and Judovits, L. H., eds ASTM, STP 1402. 

Table 8-1. Latent Heats measured in pure 8CB by different techniques. A comparison of latent heats (error bars in parentheses) from Intensity fluctuation microscopy (IFM latent heats are estimated from the measured (/q = I.2 0.I) x 10 [66] and Landau parameters in [65]), Adiabatic Scanning Calorimetry (ASC errors from [69]) and Modulated differential scanning calorimetry (MDSC errors estimated from smaller error bar). Also listed is the molar fraction X of lOCB in 8CB-10CB (alkyl-cyanobiphenyl) mixtures at which the latent heat appears to vanish...

Lafouresse et al [67] and Sied et al [68] have used Modulated Differential Scanning Calorimetry (MDSC) to measure latent heats as a function of concentration in two liquid crystal mixtures (8CB-10CB and 80CB -lOOCB). In both cases, they obtain results quantitatively differing from previous calorimetry results. 

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