MDSCs

Figure 37 MDSC thermograms for non-reversing part of heat flow for oxidised PP samples before and after S02 treatment. Reprinted from Richaud et al. [16]. Copyright 2006, with permission of Elsevier.

MDSC is particularly useful for the study of reversible (related to the heat capacity) thermal reactions, and is less useful for non-reversing (kinetically controlled) reactions. Examples of reversible thermal events include glass transitions, heat capacity, melting, and enantiotropic phase transitions. Examples of non-reversible events include vaporization,... 

The technique appears to be particularly useful in the characterization of glass transition phenomena. The utility of MDSC in the study of glass transitions can lead to methods for determination of the amorphous content in a substance [62,63]. 

Majumdar, et al. studied the role of MSCs as a stromal cell precursor capable of supporting hematopoietic differentiation in vitro by outlining the phenotypic differences between MSCs and marrow-derived stromal cells (MDSCs). Flow cytometric analysis showed that MSCs are distinct from MDSC cultures and are a homogeneous cell population devoid of hematopoietic cells [656703]. 

The differential scanning calorimeter (DSC) works on a technique that detects physicochemical transition in a system by measuring the amount of heat absorbed or released as the sample is heat across its suspected transition range. The heat absorbed or released from a sample of known mass compared with that of an empty reference pan. Modulated differential scanning calorimeter (mDSC) works on an advanced technology version of DSC, where the signal quality has been improved using... 

The portion of drug that remains trapped within the polymer may be estimated by measurfggf he the polymer-rich phase. In instances whl ef polymer-rich phase issimilartothatof neat polymer, a complete phase separation may be assumed. In other instances, the differ gsolid solubility of drug in polymer. As shown in Figure 18.12, phase separation of trehalose was observed from dextran solid dispersions in the 4-day and 34-day samples. However, a certain fraction of trehalose remained miscible with dextran as indicated by the substantially low... 

FIGURE 18.12 mDSC scans of 40% solid dispersion of trehalose in dextran when storecfQf/SOf) RH open conditions. Phase separation is seen in 4-day and 34-day samples, as indicated b fesatwslo dehydration of trehalose dehydrat% frTheTg of dextran-rich phase remains-a20°C below theTg of neat dextran (inset), indicating trehalose solubility in dextran K5(75%RH. 

As shown in Section 1.1.5 DSC, MDSC and TMDSC have provided a better understanding of changes in glass, amorphous, and crystalline phases. 

Fig. 1.45.1. Artist s view of a DSC cell in Tzero technology as used in modulated DSC (MDSC) processes. 1, Sample and reference table made from one piece of constantan 2, chromel thermocouples directly connected to the constantan tables 3, Tzero sensor from chromel-constantan in the middle between sample and reference table (TA Instruments, New Castle, DE, USA...

Solid degradation in milligram scale (using TG, DSC, and MDSC for heat of pyrolysis and specific heat)... 

MDSC, by varying the furnace temperature sinusoidally, has been used to determine the specific heat of PA6 materials (similar measurements have been performed for polypropylene nanocomposites). The materials were heated from -80°C to 250°C at 2°C/min. The reversible signal recorded during the experiment is related to the specific heat of the sample. The specific heat values versus temperature for the different PA6-based formulations are given in Figure 19.3, showing no significant differences between different formulations. The peaks noted on the specific heat curves correspond to the transition from the solid to the liquid states. 

The Arrhenius expression (Equation 19.1) using the activation energy and pre-exponential factor derived from TGA measurements of a PA6 sample in N2 was incorporated in a standard ID pyrolysis model described in Section 19.6. The thermal properties used in the model are the ones from the ignition tests (Section 19.4.2.2) as described in Section 19.6 in conjunction with the MDSC experiments (Section 19.3.2.2). Figures 19.25a-c show the predicted surface temperature histories for... 

DSC/MDSC can be used to determine the thermal and transport properties as well as the heat of melting and pyrolysis. The measurement of heat of pyrolysis is very challenging and needs more investigation. 

In this section, some case studies will be presented on the characterization of CMP pad and slurry [17-20] using such advanced analytical techniques as dynamic mechanical analysis (DMA), modulated differential scanning calorimetry (MDSC), thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA), dynamic rheometry, dual emission laser induced fluorescence (DELIF), and the dynamic nuclear magnetic resonance (DNMR). More specifically, these techniques were used to characterize (a) the effect of heat... 

The heat peaks of the nonreversing and reversing MDSC traces can be associated with nonreversible reactions such as a chemical reaction or cure and reversible reactions such as plasticizing processes in PU resin. Pad samples exposed to all tested media showed nonreversing heat peaks between 70 and 100 °C. Therefore, nonreversible chemical reactions are responsible for the pad softening. Endothermic irreversible heats reached their maximum value after approximately 180 h of exposure, as shown in Fig. 2.15. This suggests that chemical reactions that lead to pad softening are complete after approximately 180 h of exposure. 

FIGURE 2.15 Time dependence of endothermic heat related to an irreversible chemical reaction. Endothermic heat of pads soaked in pH 4, pH 11 buffer solutions, slurries, and DIW was measured using MDSC. 

MDSC, developed by TA instruments (New Castle, Detroit, U.S.A.), is based on the conventional heat flux DSC furnace design. The temperature programs differ... 

Accurate heat capacity, Cp, measurements may be obtained by DSC under strict experimental conditions, which include the use of calibration standards of known heat capacity, such as sapphire, slow accurate heating rates (0.5-2.0 K/min), and similar sample and reference pan weights. MDSC or DDSC also have been used to determine the heat capacity of several pharmaceutical materials. ... 

This new technique introduced in 1993 has been thoroughly examined and discussed. Main advantages are the separation of overlapping events in the DSC scans. In conventional DSC, a constant linear heating or cooling rate is applied. In modulated DSC (MDSC), the normally linear heating ramp is overlaid... 

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