Temperature scans, stages

Microscopic analysis is the only method available for estimating ice crystal size in ice cream. Light microscopy, equipped with cold stage and image analysis, may be used for this purpose54. Low temperature scanning electron microscopy may also be used55. 

A modified four-stage scheme (6) has been used to distinguish different rates of change of glass transition temperature during temperature scans of curing resins. These stages are defined as ... 

In general, simple one-stage reactions are probably best studied isothermally, whereas more complex systems are best investigated using temperature scanning. 

Complementary data on food and food constituents are obtained by other thermal analysis techniques, such as thermomanometry, thermogravimetry (TG), thermomicroscopy or hot stage microscopy (HSM), differential mechanical (thermal) analysis (DMA or DMTA), titration calorimetry, and microwave dielectric measurements during temperature scan. 

Cure kinetics of thermosets are usually deterrnined by dsc (63,64). However, for phenohc resins, the information is limited to the early stages of the cure because of the volatiles associated with the process. For pressurized dsc ceUs, the upper limit on temperature is ca 170°C. Differential scanning calorimetry is also used to measure the kinetics and reaction enthalpies of hquid resins in coatings, adhesives, laminations, and foam. Software packages that interpret dsc scans in terms of the cure kinetics are supphed by instmment manufacturers. 

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. 

Post C-Stage Cure (Dynamic). Samples that were C-stage cured at lAO C for 2 hours were scanned in the DMTA as a function of temperature (-100°C to 200 C). Raw data of tan delta and E vs. temperature at 30 Hz for the -5 and +5 wt.% samples is shown in Figure 10. 

A fluorometer is more sensitive than a spectrophotometer and enables a very low concentration of substrate to be used. This can be convenient in the first stage of pharmaceutical studies. Unfortunately the dependence of fluorescence intensity on temperature cannot be avoided. A blank scan at the end of the reaction enables a temperature-independent signal [45] useful for VTK processing to be obtained. The results were consistent (AS = -109 1J/K mol, AIR = 71 lkJ/mol, R2 = 0.99999) with those obtained spectrophotometrically under both CTK and VTK conditions. 

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