Differential scanning calorimetry cooling curves

Modulated differential scanning calorimetry (MDSC) curves were obtained using a Universal V2.4F TA spectrometer. First scan MDSC heating curves were obtained by heating at 5 C min to the desired temperature. Second scan MDSC heating curves were obtained by first cooling the sample after the first heating in the instrument over ca. 17 min. The sample was then heated at 5 °C min to the desired temperature. 

Figure 6. Differential scanning calorimetry scans of 1c polymers. Curves are displaced vertically. Conditions heating, 20 K/min and cooling, 320 K/min.

Levine and Slade [1.16] investigated the mechanics of cryostability by carbohydrates. Figure 1.19.1 shows an idealized phase diagram developed from differential scanning calorimetry (DSC) measurements for hydrolyzed starch (MW > 100) and for polyhydroxy combinations having a small molecular mass. With slow cooling (quasi in equilibrium conditions), no water crystallizes below the Tg curve. 

More advanced techniques are now available and section 4.2.1.2 described differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DTA, in particular, is widely used for determination of liquidus and solidus points and an excellent case of its application is in the In-Pb system studied by Evans and Prince (1978) who used a DTA technique after Smith (1940). In this method the rate of heat transfer between specimen and furnace is maintained at a constant value and cooling curves determined during solidification. During the solidification process itself cooling rates of the order of 1.25°C min" were used. This particular paper is of great interest in that it shows a very precise determination of the liquidus, but clearly demonstrates the problems associated widi determining solidus temperatures. 

Differential Thermal Analysis (DTA) — A procedure for recording the difference in temp between a substance and a reference material, against either time or temp as the two specimens are subjected to identical temp regimes in an environment heated or cooled at a controlled rate. The record is the differential thermal or DTA curve the temp difference (A T) is usually plotted on the ordinate with endothermic reactions downward and time or temp on the abscissa increasing from left to right Differential Scanning Calorimetry (DSC) —... 

Figure 7. Differential scanning calorimetry curves for anhydrous milkfat cooled at rates of 0.1° C/ min, TC/min, and 5° C/min to 5° C and stored for time periods (A) 10 minutes, (B) 1 day, (C) 7 days, and (D) 14 days.

Many techniques have been used to characterize the physical nature of solid dispersions. These include thermal analysis (e.g., cooling-curve, thaw-melt, differential scanning calorimetry and X-ray diffraction, microscopic, spectroscopic, dissolution rate, and thermodynamic methods) Usually, a combination of two or more methods is required to obtain a complete picture of the solid dispersion system. 

The use of a cooling accessory permits XRD patterns to be obtained under subambient conditions. In pharmaceutical systems, the greatest utility of the technique is to monitor the crystallization of solutes in frozen solutions. Conventionally, differential scanning calorimetry has been the most popular technique for the characterization of frozen systems. However, as mentioned earlier, this technique has some drawbacks (i) It does not enable direct identification of crystalline solid phase(s). Moreover, it is difficult to draw any definitive conclusions about the degree of crystallinity, (ii) The interpretation of DSC curves is very difficult if there are overlapping thermal events. Low temperature XRD was found to be an excellent complement to differential thermal analysis in the characterization of water-glycine-sucrose ternary systems. " ... 

Fig. 1. Differential scanning calorimetry (DSC) isothermal analysis curves of fat A. blank sample, B. sample with DK F-10, C. sample with P-170, D. sample with S-170 (Emulsifier concentration is 0.5%). Isothermal crystallization at 17°C (right side), and heating curves (left side), start at about 20°C at a rate of 5°C/min (rapidly cooled at a rateof 80°C/min). (Continued)...

FIGURE 4.1 Differential scanning calorimetry heating and cooling curves of glyceryl tri-palmitate (Dyn 116) bulk material, with microparticles prepared by solvent evaporation and microparticles prepared by melt dispersion 1 d after the preparation. The plots are displaced vertically for better visualization. (Adapted from [13] with permission from Elsevier.)... 

Differential scanning calorimetry (DSC). Dupont 900 thermal analyzer heating to 200°C, cooling to 70 °C second heating curve recorded (heating rate 10°C/min). 

Differential scanning calorimetry, DSC, is a technique which combines the ease of measurement of heating and cooling curves as displayed in Fig. 4.9 with the quantitative features of calorimetry (see Sect. 4.2). Temperature is measured continuously, and a differential technique is used to assess the heat flow into the sample and to equalize incidental heat gains and losses between reference and sample. Calorimetry is never a direct determination of the heat content. Measuring heat is different from volume or mass determinations, for example. In the latter cases the total amount can be established with a single measurement. The heat content, in contrast, must be measured by beginning at zero kelvin where the heat content is zero, and add all heat increments up to the temperature of interest. 

Using differential scanning calorimetry (DSC), one can measure the heat flow rate curve of polymer solid changing with the temperatures, as demonstrated in Fig. 6.15a. Heating (cooling) rates are constant. 

Figure 10.9. DSC heating and cooling curves (5°C/min) of cholesteryl myristate in the bulk and in colloidal dispersion (5% CM, 2% PVA PCS z-average 172 nm, PDI 0.09). With kind permission from Springer Science + Business Media Fharm. Res. Supercooled smectic nanoparticles A potential novel carrier system for poorly water soluble drugs, 21, (2004), 1834-1843, J Kuntsche et al. Abbreviations DSC differential scanning calorimetry, PVA polyvinyl alcohol, PCS Photon correlation spectroscopy, PDI Polydispersity index.

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