Amorphous internal energy

Since there is no change in internal energy when an ideal elastomer is stretched, the entire contribution to the retraction or restoring force is entropy. Unstretched elastomers are amorphous, but the random chains become more ordered when the elastomer is stretched. The modulus of an elastomer changes slightly as the temperature is reduced, but there is an abrupt change in modulus as the elastomer becomes a glassy polymer at the Tr... 

The internal energy is plotted against the pressure in Fig. 12.20. The crystal is pressurized from a to b and amorphizes between b and c the amorphous material is pressurized from c to d. The system is then depressurized from c to g. The amorphous material recrystallizes between e and f. A clear first order transition occurs between points b and c from which the transition pressure and the heat of amorphization La = U(c) — (7(b) are obtained. The observed heat of amorphization is 58 kJ/mol. During the depressurization of the system from c to g another first order phase transition occurs between points e and f from which the transition pressure and the heat of recrystallization La = t/(f) — t/(e) are obtained. The observed heat of recrystallization is — 58 kJ/mol. 

Figure 3 shows a bright-field electron micrograph and a selected-area diffraction pattern of an Al5oGe4oMnio amorphous alloy annealed for 10 min at 520 K with an internal energy lower by about 1.8kJ/mol as compared with the as-quenched amorphous phase. 

It should also be taken into account that the internal energy of a partly oriented PE may be smaller than that of an amorphous one. The energy difference will be comparable to the enthalpy difference (Ham — H ef), which was estimated by Fischer and Hinrichsen [24] to be 140 cal/mol. As function of its z-position within an otherwise undisturbed crystal a CH2 group would encounter a potential energy as shown in Figure 5.3. 

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

Stimulated by a variety of commercial applications in fields such as xerography, solar energy conversion, thin-film active devices, and so forth, international interest in this subject area has increased dramatically since these early reports. The absence of long-range order invalidates the use of simplifying concepts such as the Bloch theorem, the counterpart of which has proved elusive for disordered systems. After more than a decade of concentrated research, there remains no example of an amorphous solid for the energy band structure, and the mode of electronic transport is still a subject for continued controversy. 

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