Differential scanning calorimetry subambient

X-ray diffraction studies are usually carried out at room temperature under ambient conditions. It is possible, however, to perform variable-temperature XPD, wherein powder patterns are obtained while the sample is heated or cooled. Such studies are invaluable for identifying thermally induced or subambient phase transitions. Variable-temperature XPD was used to study the solid state properties of lactose [20], Fawcett et al. have developed an instrument that permits simultaneous XPD and differential scanning calorimetry on the same sample [21], The instrument was used to characterize a compound that was capable of existing in two polymorphic forms, whose melting points were 146°C (form II) and 150°C (form I). Form II was heated, and x-ray powder patterns were obtained at room temperature, at 145°C (form II had just started to melt), and at 148°C (Fig. 2 one characteristic peak each of form I and form II are identified). The x-ray pattern obtained at 148°C revealed melting of form II but partial recrystallization of form I. When the sample was cooled to 110°C and reheated to 146°C, only crystalline form I was observed. Through these experiments, the authors established that melting of form II was accompanied by recrystallization of form I. 

Son and coworkers also reported the syntheses of hyperbranched poly(carbosilanes) via hydrosilylation. In one report, they prepared a series of AB3 carbosilarylene monomers (5, 6 and 7)173 which polymerized cleanly and rapidly to form soluble hyperbranched polymers in high yields. The polymers, ranging in appearance from sticky solids to oils, were characterized by NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry and vapor pressure osmometry. The polymers possessed subambient Tg... 

Martini, A. Kume, S. Crivellente, M. Artico, R. Use of subambient differential scanning calorimetry to monitor the frozen-state behaviour of blends of excipients for freeze-drying PDA. J. Pharm. Sci. Technol. 1997, 51, 62-67. 

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. " ... 

Raynal S, Pezron I, Potier L, Clausse D, Grossiord JL, Seiller M. 1994. Study by differential scanning calorimetry, rheometry and electroconductimetry of mass transfers at subambient and ambient temperatures in multiple water/oU/water emulsions entrapping MgS04. Colloids Surf 91 191-205. 

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