ATHAS applications

The existence-range of the condis crystal of poly(tetrafluoroethylene), PTFE, can be seen from the phase diagram of Fig. 5.130. The calorimetric heat capacity analysis of PTFE is described as an example of the ATHAS applications in Fig. 2.63, and the entropies of transition, which lead to the high isotropization temperature, are discussed in Sect. 5.4.3. 

Although Equation (4) is conceptually correct, the application to experimental data should be undertaken cautiously, especially when an arbitrary baseline is drawn to extract the area under the DSC melting peak. The problems and inaccuracy of the calculated crystallinities associated with arbitrary baselines have been pointed out by Gray [36] and more recently by Mathot et al. [37,64—67]. The most accurate value requires one to obtain experimentally the variation of the heat capacity during melting (Cp(T)) [37]. However, heat flow (d(/) values can yield accurate crystallinities if the primary heat flow data are devoid of instrumental curvature. In addition, the temperature dependence of the heat of fusion of the pure crystalline phase (AHc) and pure amorphous phase (AHa) are required. For many polymers these data can be found via their heat capacity functions (ATHAS data bank [68]). The melt is then linearly extrapolated and its temperature dependence identified with that of AHa. The general expression of the variation of Cp with temperature is... 

The application of the ATHAS has produced a large volume of critically reviewed and interpreted heat capacity data on solid and liquid homopolymers. This knowledge is helpful in the determination of the integral thermodynamic functions which are also part of the data bank. Even of greater importance is the help these basic data give in the separation of nonequilibrium enthalpy and heat capacity effects as will be illustrated in a number of examples. 

The description of the theory of heat capacity and the application of heat capacity measurements have been given by Wunderlich and other researchers [2,3-17]. The most comprehensive and updated heat capacity data are collected in the ATHAS data bank (Advanced THermal Analysis) which has been developed over the last 25 years by Wunderlich (Chemistry Department, The University of Tetmessee), and coworkers. 

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