Stepwise quasi-isothermal MTDSC

More complex temperature programmes are sometimes useful. These might combine periods of variable heating and cooling rates with isothermal periods. For example, stepwise heating can be used to detect the onset of melting under quasi-isothermal conditions (Laye, 2002). Modulated temperature DSC (MTDSC), in which the linear temperature scan is perturbed by a sinusoidal, square or saw-tooth wave, or other modulation of temperature, has a number of potential advantages over the conventional linear scan. These include increased sensitivity and resolution, and the ability to separate multiple thermal events (Laye, 2002). 

The potential of MTDSC for the real-time monitoring of reaction-induced phase separation is demonstrated with the cure of an epoxy— aniline-polyethersulphone (PES) mixture [80,104], The epoxy-aniline system allows following the isothermal cure accurately above and below goo (94°C), Choosing an isothermal cure temperature below will provoke a combination of phase separation of a PES-rich phase and vitrification of the epoxy-aniline matrix. Figure 2,17 shows the quasi-isothermal cure at 80°C for both modified and unmodified epoxy-aniline systems. The effect of primary and secondary amine reactions is seen as a positive A Cp,react- In the unmodified system, vitrification is seen after 91% conversion as a stepwise... 

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