Transition properties polymer thermodynamics

The transition from a glass to a rubberlike state is accompanied by marked changes in the specific volume, the modulus, the heat capacity, the refractive index, and other physical properties of the polymer. The glass transition is not a first-order transition, in the thermodynamic sense, as no discontinuities are observed when the entropy or volume of the polymer is measured as a function of temperature (Figure 12.2). If the first derivative of the property-temperature curve is measured, a change in the vicinity of is found for this reason, it is sometimes called a second-order transition (Figure 12.2). Thus, whereas the change in a physical property can be used to locate Tg, the transition bears many of the characteristics of a relaxation process, and the precise value of can depend on the method used and the rate of the measurement. 

The roots of this method can be traced back to the pioneoing work of the Rosenbluths in the 1950s [64]. However, the CCB method in reality is a direct descendant of the Scanning method of Meirovich [65-68], in partkular of the version for attractive random walks [68]. A related idea was introduced by Harris and Rice [69]. The method has recently attracted much intnest, and has been fully developed as a simulation tool through the work of Siepmann [42], Frenkel et al. [43], and Siepmann and Frenkel [44]. de Pablo et al. [45] implemented the CCB method for the off-lattice treatment of realistic polymer systems. The initial off-lattice applications have demonstrated that the method can be used in a wide variety of important problems in polymer systems, most notably the determination of equilibrium thermodynamic properties, chemical potentials of polymers, soluUlitks d gi t mol ades in polymer melts, studies of phase transitions, and polymer-sdivent interactions in supercritical fluids [70-72]. 

In summary, TPPs show complicated phase transition behaviors. Their phase diagrms are established and various phases are identified via the thermodynamic transition properties obtained from DSC, the structural order and symmetry determined by WiOCD, and morphology and defects observed under PLM and TEM. In particular, the WAXD fiber patterns in different phases play the most important role in determining the phase structures and symmetry. It is evident that the concepts of highly order smectic phases developed in small-molecule liquid crystals can also be utilized in the main-chain liquid crystalline polymers. 

The glass transition and other transitions in polymers can be observed experimentally by measuring any one of several basic thermodynamic, physical, mechanical, or electrical properties as a function of temperature. Recall that in first-order transitions such as melting and boiling, there is a discontinuity in the volume-temperature plot. For second-order transitions such as the glass transition, a change in slope occurs, as illustrated in Figure 8.5 (9). 

Important characteristics that describe static mass, conformations, and dimensions of polymer molecules have been surveyed. This has been followed by hydrodynamic properties such as diffusion and viscosity. A separate section has been used to describe the salient aspects of charged polymers and colloids in solution. From there, the collective properties of polymers were briefly introduced in terms of their solution thermodynamics, the relationship of these to the scattering of light, and to phase behavior and transitions. Concentrated polymer solutions and melts become extraordinarily complex, with time response behavior depending on polymer architecture and interactions, and this has been briefly discussed in the area of rheology. In the solid-state limit of rheology, polymers take on myriad applications in materials engineering applications, in electronics, optics, and other areas. 

It is known that the properties of polymers can be changed essentially because of their physical (heat) ageing. This process is considered as a transition to a thermodynamically more equilibrium state [89] and different parameters were used... 

Transitions in polymers are rapidly and conveniently studied using differential scanning calorimetry (DSC). Small samples of the polymer and an inert reference substance (one that undergoes no transitions in the temperature range of interest) are mounted in a block with a heater for each and thermocouples to monitor temperatures. The thermodynamic property monitored here is the enthalpy. A servo control system adjusts and measures the power to the heaters to maintain the sample and reference temperatures the same as the sample is... 

In this Chapter, we will investigate thermodynamic properties of aggregation transitions of polymers and peptides from different perspectives of statistical analysis. 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

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