Amorphous mixing energies

O. Pachoumi, C. Li, Y. Vaynzof, K. K. Banger and H. N. Sirringhaus, Improved Performance and Stability of Inverted Organic Solar Cells with Sol-Gel Processed, Amorphous Mixed Metal Oxide Electron Extraction Layers Comprising Alkaline Earth Metals, Adv. Energy Mater.,2013,3(11), 1428-1436. 

Polymers don t behave like the atoms or compounds that have been described in the previous sections. We saw in Chapter 1 that their crystalline structure is different from that of metals and ceramics, and we know that they can, in many cases, form amorphous structures just as easily as they crystallize. In addition, unlike metals and ceramics, whose thermodynamics can be adequately described in most cases with theories of mixing and compound formation, the thermodynamics of polymers involves solution thermodynamics—that is, the behavior of the polymer molecules in a liquid solvent. These factors contribute to a thermodynamic approach to describing polymer systems that is necessarily different from that for simple mixtures of metals and compounds. Rest assured that free energy will play an important role in these discussions, just as it has in previous sections, but we are now dealing with highly inhomogeneous systems that will require some new parameters. 

In Ref. 67, the increase in bandgap of the as-deposited film was attributed to a mixed amorphous-polycrystalline structure (apparently no XRD pattern was found for the as-deposited film). The onset of absorption in the transmission spectrum was sharp for the as-deposited film, and any polycrystalUne (nonquantized) material would be expected to give some absorption at lower energies, even if the amorphous phase possessed a higher bandgap. Therefore size quantization seems to be a more reasonable explanation for the high bandgap of the as-deposited film. 

Assuming random mixing in the amorphous lamellae and the melt, the non-combinatorial free energy change per mole of segments on mixing can be written... 

Parallel-plate reactor Dissociation of CH4 for amorphous carbon Well mixed Mean electron density energy distribution measured with Langmuir probe 82... 

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