Step scan DSC

The nonreversing effects can be noted in the IsoK baseline (Ye 2006). The IsoK baseline is the heat flow curve at zero ramping or for the isothermal hold after the ramp. In Fig. 2.119 the signals for the step scan DSC are shown, the IsoK baseline can be noted in the raw data following the return to baseline after the ramp segment. Slight overshoots in the heat flow may occur as the calorimeter obtains steady state. 

Step scan DSC has also shown the abihty to separate cold crystallization from the glass transition as was noted for freeze-dried poly(L-lactide), PLLA (Sasaki et al. 2005). Separation of the cold crystallization can be noted in the Fig. 2.121 for PLLA sample A using a freeze-drying apparatus (PLLA-FDA). Heating rates of 5°C/min with 2°C steps were used. 

Melting Step scan DSC has been used to study a number of melting processes. Papageorgiou et al. (2006) investigated the effects of annealing at different temperatures for different molecular masses of poly(l,3-propylene terephthalate) samples. Step ramp rates of 5 °C/min were utilized... 

A time-domain technique analogous to TMDSC is the step-scan DSC. [ 17] One primary advantage of both the step scan and TMDSC methodology is that the instrumental baseline is unimportant for measurement of Cp since the incremental heat flow response is measured... 

Figure 3 Absolute Cp versus temperature for poly(a-methyl styrene)/pentamer mixtures obtained using step-scan DSC. After ref 18.

Figure 4 Absolute Cp versus temperature for polystyrene stacked thin film samples as a fimction of film thickness obtained using step-scan DSC arrows indicate Tg for the bulk and 17 nm film samples, respectively. After ref 26.

An extreme example of this is the protein plasminogen, which denatures in at least seven steps. The DSC trace of successive scans obtained from heating a solution of plasminogen is shown in Figure 16.10. Using statistical mechanical techniques, Privalov and his colleagues were able to deconvolute the observed... 

Further recent developments in DSC and IR techniques, with respect to the study of SC barrier properties, include step-scan FT-IR photoacoustic spectroscopy [195] and combined microscopic differential calorimetry-Four-ier transform infrared (DSC-FTIR) spectroscopy [196]. The former allows depth profiling of the membrane the latter enables the simultaneous detection of calorimetric and structural modifications during a thermal transition. Technological advances in DSC and IR will, no doubt, continue to expand the application of these techniques to the study of skin barrier function. 

Papageorgiou, G.Z., Achilias, D.S., Karayannidis, G.P., Bikiaris, D.N., Roupakias, C., and Litsardakis, G. (2006) Step Scan TMDSC and High Rate DSC study of the multiple melting behavior of poly(l,3-propylene terephthalate). Fur. Polym. /., 42, 434-445. 

In the step-scan alternating DSC (SSA-DSC), the temperature program comprises a periodic succession of short, Unear heating and isothermal phases the measured heat flow contain thus fractions which arise from the heat capacity and those due to physical transformations or chemical reactions [7]. 

PieUchowski K, Flejtuch K, PieUchowski J (2004) Step-scan alternating DSC study of melting and crystaUisation in poly(ethylene oxide). Polymer 45 1235-1242... 

Figure 1.16 The heat capacity trace of PET cooling at 200°C/min using fast scan DSC. The Tg is clearly shown as a step similar to that found on heating.

The progress of polymer degradation may be followed by a wide variety of techniques, some of them being mentioned at the right column in the Bolland-Gee scheme (Scheme 2). There are techniques that directly monitor some of the elementary reaction steps such as, for example, oxygen absorption (reaction 2), differential scanning calorimetry (DSC) (reaction 3), chemiluminescence (reaction 11) analytical and/or spectral methods of determination of hydroperoxides, etc. 

When a number of polymorphs are identified in step one they should be characterized by Differential Scanning Calorimetry (DSC) to obtain AHm and Tm data. This information confirms their relative stabilities with respect to temperature. If DSC data cannot be obtained then slurry experiments should be performed. It is always good practice to confirm the relative stability with sluny experiments because DSC traces can be difficult to interpret correctly, and can mask subtle effects. 

The first directly-measured evidence that C—H bond rupture in the methyl group is the rate-determining step in the thermal de compn of TNT has been obtained with isothermal differential scanning calorimetric (DSC) analysis using deuterium isotope effects (Ref 96), DSC analysis has also been used to determine the kinetic parameters of thermal decompn (Ref 92). Others (Ref 101) have also studied the mechanism of the reaction using the deuterium isotope effect. Data are available on heat generation in... 

PHOSPHOLIPID SYNTHESIS. Phospholipids were synthesized (H.Schuster, S.S. Hall, and R.Mendelsohn, in preparation) according to the procedures of Tulloch (26), modified with more modern and efficient coupling steps, and scaled up to produce 2-3 grams of specifically deuterated material. Derivatives were fully characterized with NMR, MS, FT-IR, and Differential Scanning Calorimetry (DSC). Purity is estimated from NMR data at > 98X. The extent of deuteration, as estimated from the residual intensity of the CHD rocking modes at... 

The next step in the analysis involves the use of DSC to observe the virgin melting profile. If a melt endotherm is not encountered, then the scan can be continued up to roughly 340°C to check for crosslinking exotherms. 

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