Doping-proton association

Sulfate-doped zirconia was found to have both Lewis and Brdnsted add sites on the surface, where the sulfate groups were the carrier of the protonic site. The ratio of Lewis to Br0nsted sites was found to vary depending on heat treatment, but the percentage of sulfate groups associated with a proton was found to be constant at 12-17%. 

One of the problems associated with the use of heterocycles is that the intrinsic concentration of protonic charge carriers can only be moderately increased through acid doping (also see Section 4.3). This is particularly the case when the dynamics within the hydrogen-bonded domain is highly constrained through immobilization (especially in fully polymeric systems), which is probably the direct consequence of a reduced dielectric constant. This also leads to a further increase of the Haven ratio... 

Figure 15.15. ll HR-MAS NMR spectra of a whole soil swollen in D20 and doped with trifluralin (A). II HR-MAS spectra whole soil swollen in D20 (B). For C-III and C-IV, dashed lines indicate the unbound trfluralin while solid lines with brackets indicate the bound trifluralin. protons II are masked by the ahphatic signals from the soil. Reprinted from Simpson, A. J., Kingery, W. L., Shaw, D. R., et al. (2001b).The apphcation of H HR-MAS NMR spectroscopy for the study of structures and associations of organic components at the solid—Aqueous interface of a whole soil. Environ. Sci. Technol. 35, 3321-3325, with permission from the American Chemical Society. 

Polyaniline differs from other CPs in that the doping process may be associated with protonation of the N atoms in the chain (i.e., to a base <- salt equilibrium in the presence of acid, in addition to the usual redox reactions). This is discussed further in Chapter 13. The related processes are therefore more complex. On the other hand, the low cost and proces-sibility of PAni makes it a prime candidate for several applications. 

Nanocrystalline MgO possessing superbasic sites has been prepared by the doping of potassium atoms using vapor diffusion (Sun and Klabunde, 1999a). This creates K+ and e sites on the crystal surface where the free electron associates with surface sites to produce superbasic reactive zones. Exposure of alkenes to this material result in the formation of allyl anions, formed by proton abstraction, which can alkylate ethane see reaction (17.9) ... 

HF molecules are held to occupy oxygen sites in the ice lattice. Since only one proton is associated with the fiuoride ion, each acid molecule introduces into the lattice one L type valence defect. In addition, HF is held to ionize according to the mass-action law, so that at a given temperature the number of ions increases with the square root of the concentration. Thus, in ice doped with HF there are hydronium ions from the dissociation of both the water molecules and the HF impurities. The negative ions, OH and F", are believed to have a very much lower mobility and are therefore neglected. Table III gives the relations obtained... 

Hall and Williams reported that some of their films were made up of singlecrystal platelets parallel to the surface of the substrate and having areas of approximately 1000 nm and a thickness of 100 nm (film thickness) [95, 96]. This was determined by the use of both a polarizing microscope and by a scanning electron microscope. The structure of thicker films, produced by multiple evaporations of Pb and conversions to Pb(N2)3, such as used for the far-infrared work, was not reported [95,96,120]. However, the thick films were homogeneous as detected by Rutherford back-scattering of protons [128]. There is also evidence that the disorder was variable from film to film because of variations in the resolution at room temperature of the maximum in the optical extinction at 375 nm [95, 96, 122, 129]. As discussed above, this maximum is sensitive to irradiation, doping, and heat treatment. The resolution of this peak and the associated imperfections in the film are also apparently dependent on the details of the preparation techniques. 

Two major changes are associated with the redox switching process in ECPs one is the charge of the polymer chains that induce ionic motion to maintain electroneutrality (and in the particular case of PANI, possibly proton exchange [179]) the other one is related to the hydrophobic/hydrophUic balance of the polymer matrix that makes the solvent play an important role in the doping process and often induce swelling phenomena [180]. It has been shown that counterion insertion during oxidation of PPy is accompanied by desolvation processes as evidenced by variation of the diffusion coefficient of the counterion [181]. These desolvation processes could be involved in the achievement of the quasi-metallic state of ECP [182]. 

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