Mobility dipolar disorder

The concentration dependence of a was described by the dipolar disorder model. Due to the low dipole moments of ENA-B and the PS repeat unit, Sinicropi et al. argued that the dipolar components can be neglected and the total width of the DOS is determined only by the van der Waals component. The results yield a van der Waals components of 0.079 to 0.090 eV that increase as the ENA-B concentration decreases. The low values of the van der Waals component and the high prefactor mobilities are the reasons for the high mobilities of ENA-B doped PS. The degree of positional disorder and the wave-... 

Thus far, electron transport layers have not been used in commercial applications. Positively charged photoreceptors have been either single-layer or have the generation layer uppermost. Because of the influence of dipolar disorder on mobilities, acceptor molecules must have a combination of a low reduction potential, high solubility, and low dipole moment. This combination has thus far proven elusive. 

Since dipolar disorder (or, empirically, the presence of polar eomponents) is a major factor governing the mobility, it is worthwhile to make several additional comments on the subject. 

The applications of solid-state C-NMR spectra for the study of polymorphs and solvates can go beyond evaluations of resonance band positions and make use of additional spectral characteristics. For instance, studies of relaxation times of furosemide polymorphs were used to show the presence of more molecular mobility and disorder in Form II, while the structure of Form I was judged to be more rigid and uniformly ordered [158]. The analysis of the solid-state C-NMR spectra of (li ,3 j-3-/ -thioanisoyl)-l,2,2-trimethylcyclopentanecarboxylic acid was facilitated by the 7-modulated spin-echo technique, which was used to deduce the number of protons bound to each carbon atom [159]. Differences in the dipolar dephasing behavior between the two polymorphs of ( )- ra 5-3,4-dichloro-A/-methyl-7V-[ 1,2,3,4-tetrahydro-5-methoxy-2-(pyrrolidin-1 -yl)]naphth-1 -yl-benzeneacetamide were noted and ascribed to motional modulation of the carbon-hydro-... 

Additional questions are raised when the moving ion is immersed in water instead of a simple dipolar liquid discussed in Sec. 5.4.The hydration phenomena observed by many different experiments show a remarkable variety in its dependence on size and sign of ions, which may not be characterized by a simple chemical model such as ion-water complex formation, or a solventberg model. Such a model seems to apply to very small monovalent ions like Li+ and F and multi-valent ions which make a stable hydration shell with substantial lifetime. However, water molecules in the first hydration shell around ions with greater size are more mobile and disordered than those in bulk water. The behavior which has been referred to as structure breaking by Frank and Wen [85] and as negative hydration by Samoilov [86] is due to the competition between two forces acting on water molecules in the shell, the... 

Both for the SDS/CA/waler and the CMEA/CA/water systems, the all-trans signal disappears above the upper phase transition temperature. The signal of disordered chains is usually of lower intensity since cross-polarization, which requires a dipolar coupling between H and C nuclei, is less efficient for mobile chains. Cross-polarization breaks down completely for liquid-like chains with isotropic mobility since the dipolar coupling is averaged to zero. Highly mobile chains can be observed better by using direct carbon excitation instead of cross-polarization. 

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