Crystallinity transport properties

The preceding structural characteristics dictate the state of polymer (rubbery vs. glassy vs. semicrystalline) which will strongly affect mechanical strength, thermal stability, chemical resistance and transport properties [6]. In most polymeric membranes, the polymer is in an amorphous state. However, some polymers, especially those with flexible chains of regular chemical structure (e.g., polyethylene/PE/, polypropylene/PP/or poly(vinylidene fluoride)/PVDF/), tend to form crystalline... 

The comparison between predicted and experimental spectra allows a validation of the methods and provides suggestions for the interpretation of the relevant phenomena in terms of changes of the molecular electronic structure and equilibrium geometry. In particular, the study carried out on thiophene dimers clearly points out the relevant role of 77-77 interactions occurring in the stacks of molecules characteristic of the solid crystalline phases. The fundamental importance of this kind of interaction has been recently demonstrated by studies [35] dealing with the charge transport properties of new conjugated molecular materials suitably synthesized for application in the field of molecular electronics [36],... 

In addition to the opportunities for new materials synthesis and characterization along these lines, transport properties, rheology, and processing techniques for liquid crystal polymers are essentially unexplored. Experiences with synthesis of polymer structure based on these liquid crystal templates may open up other creative avenues for template synthesis, for example, inside other crystalline structures, chlathrates, or zeolites, or on surfaces [4], Composites, alloys, or mixtures of liquid crystalline and flexible polymers may produce new materials. 

The transport properties of such disordered materials (see Section II) are difficult to study, for several reasons. One is that the microscopic theory of transport is not clear even for perfectly ordered CPs, as discussed in the reviews mentioned above. Another is that a dc or low-frequency conductivity measurement on an inhomogeneous material can be viewed as measuring several resistances in series, the larger playing the major role. For instance, in a fibrillar material interfibril transport is important, in a mixed crystalline-amorphous medium the amorphous regions may limit... 

This chapter begins a series of chapters devoted to electronic structure and transport properties. In the present chapter, the foundation for understanding band structures of crystalline solids is laid. The presumption is, of course, that said electronic structures are more appropriately described from the standpoint of an MO (or Bloch)-type approach, rather than the Heitler-London valence-bond approach. This chapter will start with the many-body Schrodinger equation and the independent-electron (Hartree-Fock) approximation. This is followed with Bloch s theorem for wave functions in a periodic potential and an introduction to reciprocal space. Two general approaches are then described for solving the extended electronic structure problem, the free-electron model and the LCAO method, both of which rely on the independent-electron approximation. Finally, the consequences of the independent-electron approximation are examined. Chapter 5 studies the tight-binding method in detail. Chapter 6 focuses on electron and atomic dynamics (i.e. transport properties), and the metal-nonmetal transition is discussed in Chapter 7. 

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