Differential scanning calorimetry transition

Phase transitions in potassium (T = 334 K) and rubidium (T = 320 K) acrylates have been established by wide-line n.m.r. and differential scanning calorimetry. Transitions were not observed for Li and Na salts. The i.r. spectrum of HCO2K in KBr discs is variable. The spectra obtained all proved to be superpositions of two spectra, one due to the original solid, and the other to a transformation product, formed when pressure was applied. 

The product must be formulated and frozen in a manner which ensures that there is no fluid phase remaining. To achieve this, it is necessary to cool the product to a temperature below which no significant Hquid—soHd phase transitions exist. This temperature can be deterrnined by differential scanning calorimetry or by measuring changes in resistivity (94,95). 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

Transitions such as T and are rapidly and conveniently studied using differential scanning calorimetry (dsc). This technique monitors changes in... 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Fig. 10. Differential scanning calorimetry of cellulose triacetate. Second heating at 20°C/min. glass-transition (T temperature = 177 " C crystallization on heating (T)/j) = 217 C melting temperature (Ta) = 289 C. To convert to cal, divide by 4.184.

The solid-liquid transition temperatures of ionic liquids can (ideally) be below ambient and as low as -100 °C. The most efficient method for measuring the transition temperatures is differential scanning calorimetry (DSC). Other methods that have been used include cold-stage polarizing microscopy, NMR, and X-ray scattering. 

Differential scanning calorimetry (DSC) is fast, sensitive, simple, and only needs a small amount of a sample, therefore it is widely used to analyze the system. For example, a polyester-based TPU, 892024TPU, made in our lab, was blended with a commercial PVC resin in different ratios. The glass transition temperature (Tg) values of these systems were determined by DSC and the results are shown in Table 1. 

The modified NBR samples were characterized by differential scanning calorimetry [11,78-80,98]. The glass-transition temperature (T ) decreased with the level of hydrogenation. In the case of HFNBR, Tg increased with an increase in the addition of aldehyde groups to the polymer chain. Thermogravimetric analysis of the modified polymers have also been carried out [15]. 

Strict control of the fusion process is imperative. In addition to thickness, hardness, continuity and adhesion checks, correct cure may be assessed by differential scanning calorimetry techniques, which are designed to measure any difference in the glass transition temperature of a laboratory-cured powder and the cured coating taken from the factory-coated pipe. 

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are also very useful tools for the characterization of polymers. TGA and DSC provide die information about polymer stability upon heating and thermal behaviors of polymers. Most of the polymers syndiesized via transition metal coupling are conjugated polymers. They are relatively stable upon heating and have higher Tgs. 

Triethanolamine salts of alcohol sulfates form white crystals when obtained in pure form after recrystallization. At their melting point they are semisolid with gelatinous appearance and the transition is difficult to detect. Melting points, determined through thermograms obtained by differential scanning calorimetry, gave 72, 76, 80, and 86°C for dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates, respectively [63]. 

Structured proteins have also been investigated by thermal analysis [40,41], denaturing resulting in an endotherm which is readily detected by differential scanning calorimetry (DSC). DSC of recombinant resilin in the swollen state showed no transitions over a wide temperature range (25°C-140°C), further evidence of the absence of any strucmre. This is in contrast to the strucmred proteins wool and bovine serum albumin, which show denamration endotherms at 145°C and 62°C, respectively (Figure 9.6). 

Luan CH, Harris RD, Prasad KU et al (1990) Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogs. Biopolymers 29 1699-1706... 

Figure 10.7 The phase diagram (a) and the glass transition temperatures (b) of a PSC/PVME mixture obtained, respectively, by light scattering and differential scanning calorimetry (DSC). Irradiation experiments were performed in the miscible region at 127 C indicated by (X) in the figure of trans-cinnamic acid-labeled polystyrene/poly(vinyl methyl ether) blends.

Method employed to establish first-order character of transition cal = calorimetry DSC = differential scanning calorimetry X-ray = X-ray diffraction ME = Mossbauer effect... 

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