Aqueous solutions dispersion-derivative measurement

An alternative technique for the measurement of sc is to study the photopotential. The theory of this is discussed in some detail in Sect. 7, but the essential features of the measurement are shown in Fig. 16. After equilibration in the dark, when the potential of the electrode at open circuit becomes equal to the redox potential Vredox, the light is turned on and the electrode potential changes at open circuit in such a way that the bands become flat. There are many problems with this technique and it is considerably less reliable than a properly conducted a.c. experiment, but it may give a reasonably accurate picture if surface recombination is small (vide infra). Some results for p-GaAs in aqueous solution are shown in Fig. 17 and the S values derived are of the order 0.7, though the dispersion apparent in Fig. 17 makes a quantitative interpretation difficult. 

Excited State Lifetime Measurements Corroborative evidence for an expanded water-swollen PAA structure across the entire pH range has been derived from excited state lifetime measurements [20,65,87,119]. For example, pyrene 10 5M was dispersed as a probe in a dilute PAA aqueous solution (10 2wt% w/v)... 

The derivatives ZrP EtOj were dispersed in aqueous solutions containing varied amount of alkali salts MX (M=Li, Na, K, and Cs X=SCN, I, Br, and NO3), and then evaporated to dryness at 90 C together with the salts. The basal spacings of the dried samples were measured by an X-ray diffractometer with a nickel-filtered Cu Ka radiation in comparison with the spacings of the initial ZrP-EtOj. ... 

The knowledge of the surface potential for the dispersed systems, such as metal oxide-aqueous electrolyte solution, is based on the model calculations or approximations derived from zeta potential measurements. The direct measurement of this potential with application of field-effect transistor (MOSFET) was proposed by Schenk [108]. These measurements showed that potential is changing far less, then the potential calculated from the Nernst equation with changes of the pH by unit. On the other hand, the pHpzc value obtained for this system, happened to be unexpectedly high for Si02. These experiments ought to be treated cautiously, as the flat structure of the transistor surface differs much from the structure of the surface of dispersed particle. The next problem may be caused by possible contaminants and the surface property changes made by their presence. 

Kunz W, BeUoni L, Bernard O, Ninham BW (2004) Osmotic coefficients and surface tensions of aqueous electrolyte solutions role of dispersion forces. J Phys Chem B 108 2398-2404 Lee L-H (2000) The gap between the measured and calculated liquid-liquid interfacial tensions derived from contact angles. J Adhesion Sci Technol 14 167-185 Li ZX, Lu JR, Styrkas SA, Thomas RK, Rennie AR, Penfold L (1993) The structure of the surface of ethanol/water mixtures. Mol Phys 80 925-939 LoNostro P, Fratoni L, Ninham BW, Baglioni P (2002) Water absorbency by wool fibers hofmeiter effect. Biomacromol 3 1217-1224... 

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