DSC data, using

Simulations of DSC data using these expressions demonstrate that unfolding of an oligomer leads to an asymmetric endotherm (Fig. 8). Because of the asynunetry of the transition, the temperature of the midpoint of the transition, T , is not the same as the maximum of the DSC endotherm or the inflection point of the progress curve. " By definition, a(T) is equal to 0.5 at the T , and since... 

A thermal scan showed that the exotherm of the principal reaction can be significant if the system is neither controlled nor vented. From isothermal studies (i.e., experiments at constant temperature), time-to-maximum rate was determined which was comparable to that obtained from the DCS data. The larger scale data showed, not surprisingly, more rapid reactions at elevated temperatures. Thus, it was decided to use the DSC data at lower temperatures, and the larger scale test data at higher temperatures for hazard evaluation. 

Differential thermal analysis (DTA) Chemical testing technique that produces similar data to DSC. DTA uses temperature differences to generate test results DSC has largely replaced the DTA technique as a screening tool for obtaining chemical hazard test data... 

GPC measurements were used to demonstrate that a monomodal molecular weight distribution with a polydispersity of approximately 2 was obtained. The glass transition temperature was determined on a Perkin-Elmer DSC-2 using a heating rate of 10 C/min and the intrinsic viscosity was determined in NMP at 25°C. These data are summarized in Table I. 

Deconvolution Analysis of DSC. Data analysis was carried out using the DECONV section of the DA-2 software package. This software, which is based on the deconvolution procedure of Freire and Biltonen (4), allows deconvolution of differential heat-capacity peaks either as the result of simple addition of multiple independent transitions or as the result of more complex mathematical processes representing the combination of transitions that interact in such a way that an obligatory reaction sequence is imposed (sequential transitions). 

Although the simple rate expressions, Eqs. (2-6) and (2-9), may serve as first approximations they are inadequate for the complete description of the kinetics of many epoxy resin curing reactions. Complex parallel or sequential reactions requiring more than one rate constant may be involved. For example these reactions are often auto-catalytic in nature and the rate may become diffusion-controlled as the viscosity of the system increases. If processes of differing heat of reaction are involved, then the deconvolution of the DSC data is difficult and may require information from other analytical techniques. Some approaches to the interpretation of data using more complex kinetic models are discussed in Chapter 4. 

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... 

Behme and Brooke (1991) have derived an equation for estimating the solubility ratio of two polymorphs at a given temperature using DSC data on the enthalpy of fiMty) nd the melting temperature of each form. The free energy of the transition orthe natural logarithm of the solubility ratio multiplied byRT (Equation 19.6) was estimated by the difference between the solubility estimates for each form calculated by Equation 19.10 ... 

One study specifically designed for PEFC was reported by Thompson et al.8 They used a direct current to measure the proton conductivity at low temperature. In conjunction with the DSC data, they found the dependency of crossover temperature (temperature where the activation energy changes) on water content and hysteresis between freezing and melting. 

Differential Scanning Calorimetry (DSC) was used for a long time in the field of process safety [21-23], This is essentially due to its versatility for screening purposes. The small amount of sample required (micro-calorimetric technique) and the fact that quantitative data are obtained, confer on this technique a number of advantages. The sample is contained in a crucible placed into a temperature controlled oven. Since it is a differential method, a second crucible is used as a reference. This may be empty or contain an inert substance. 

With the use of eqn. (2.32), it is now easy to take the DSC data and find the models that best describe the curing reaction. 

The energy involved in the folding and association of copolymer chains in solutions can be measured by a micro-calorimeter (MicroCal Inc). We used US-DSC at an external pressure of 180 kPa. The cell volume is only 0.157 mL. The heating rate can be varied and the instrument response time is normally a few seconds. All the DSC data should be corrected for instrument response time and can be analyzed using the software in the calorimeter. Note that the concentration used in DSC is normally not lower than 10-3 g/mL, much higher than that used in LLS (10 6-10 3 g/mL). 

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