Gibbs-DiMarzio second-order

However, if the Tg is explained according to the Gibbs-DiMarzio second-order transition theory, it may be expected that not only the... 

Both kinetic and thermodynamic approaches have been used to measure and explain the abrupt change in properties as a polymer changes from a glassy to a leathery state. These involve the coefficient of expansion, the compressibility, the index of refraction, and the specific heat values. In the thermodynamic approach used by Gibbs and DiMarzio, the process is considered to be related to conformational entropy changes with temperature and is related to a second-order transition. There is also an abrupt change from the solid crystalline to the liquid state at the first-order transition or melting point Tm. 

We have replaced the idea of second order phase transition postulated by the Gibbs-DiMarzio theory, yet retained its successful features. Tr is treated as the thermodynamic anomaly at which the most stable hole configuration is reached under the close packing of holes and flex bonds. 

Gibbs and DiMarzio (34, 33) developed a theory for a second order transition in polymers based on the quasi-lattice theory and taking into... 

The Gibbs-DiMarzio approach, as has been stated, rests on the existence of a true second-order thermodynamic transition at a temperature T2 below the observed Tg. The pressure dependence of T2 can thus be obtained by the methods of equilibrium thermodynamics. For a first-order phase transition, the pressure dependence of the transition temperature is given by the Clapeyron equation... 

The entropy theory of the glass transition was developed by Gibbs and DiMarzio and by Adams and Gibbs to describe polymeric systems. By mixing the polymer links with holes or missing sites on a lattice to account for thermal expansion as in a lattice gas model, they could determine the entropy of mixing and the configurational entropy of the polymer. They found a second-order transition at a temperature They then pointed... 

Figure 5.20 Entropy (5) as a function of temperature (T) and pressure (P) according to the Gibbs-DiMarzio theory. The second-order transition (denoted T2 by the authors) is marked with a thick line. Drawn after DiMarzio (1981).

Figure 13 Schematic representation of the SPT surface calculated from the Gibbs-DiMarzio lattice model. The mean-field calculation on the lattice model results in a second-order transition in the Ehrenfest sense (after ref. 16, with permission)...

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