Surface charge, measurements

The intercept of this line is a function of cKci-. Thus, this theory predicts that the Oo/pH curves at various concentrations should all tend to become parallel lines far from the pHpzc. This is indeed the usual experimental observation. The slope of the adsorption capacitance follows directly from surface charge measurements. This had already been noted by Smit (21). The intercept of the straight line predicted by Equation 37 can be used to find cKCi-, provided that as and cdl are known. 

Resistance or resistivity is by far the property most often measured. For anti-static and conductive rubbers, only resistivity and surface charge, measurements are useful because such rubbers would not be used in situations requiring low dielectric loss or involving high voltages. 

After an overview over the experimental techniques and results from the literature (Sect. 7.2) and some words about technical aspects and our experience concerning problems with some materials (Sect. 7.3), the experiments of the authors can be outlined as follows first, measurements of ohmic and capacitive currents in the contact mode are described (Sect. 7.4), followed by a description of some surface charge measurements in the non-contact mode (Sect. 7.5). The chapter closes with some experiments to probe electro-mechanical properties by the use of piezo response microscopy (Sect. 7.6) with its own brief literature overview. All three experimental parts are opened by a short introduction to the SFM techniques implemented in our lab. 

Hydrous sodium titanate was prepared by the method of Dosch and Stephens (1). Titanium isopropoxide was slowly added to a 15 wt% solution of sodium hydroxide in methanol. The resulting solution was hydrolyzed by addition to 10 vol% water in acetone. The hydrolysis product is an amorphous hydrous oxide with a Na Ti ratio of 0.5 which contains, after vacuum drying at room temperature, approximately 13.5 wt% water and 2.5 wt% residual alcohol. The ion-exchange characteristics of the sodium titanate and the hydrolysis behavior of the nickel nitrate solutions were characterized using a combination of potentiometric titrations, inductively coupled plasma atomic emission (ICP) analysis of filtrates, and surface charge measurements obtained using a Matec electrosonic amplitude device. 

The titratable surface charge measurements can be interpreted to give a quantitative assessment of the interactions between the solid and the supporting electrolyte ions. Potentiometric titrations measure the adsorption or release of protons and the model developed by Yates ad. (29) and Davis et al. (17) proposes reactions between oxide surface groups and... 

Regarding the source of electrosorption information, the situation is the same as with double layers without adsorbed organics most of it is obtained on mercury. Few common organic molecules have escaped such measurements. Electrosorption on charged colloids as such has also been abundantly investigated, but systematic combination with surface charge measurements is relatively rare this will be the theme of the present section. Electroklnetic or stability measurements are sometimes enlightening but are insufficient to understand the composition and fine-structure of the adsorbate. 

The quantities, which have been directly measured are referred to rather than those which were derived from the measured data. For example when the adsorption of counterions was assumed to entirely balance the surface charge (measured directly), the results are listed under charge rather than under adsorption of counterions , even if the later was used in the title of the paper, abstract and figure captions. 

Figure 3.18. Estimates of the net surface charge of an oxisol A-horizon using the method of anion and cation adsorption (AEC — CEC) and the method of acid-base titration (H -OH ). The point of zero charge (PZC), based on the AEC — CEC curve, is 3.86. (Adapted from E. Marcano-Martinez and M. B. McBride, 1989. Comparison of the titration and ion adsorption methods for surface charge measurement in oxisols. Soil Sci. Soc. Am. I. 53 1040-1045).

Marcano-Martinez, E. and M. B. McBride. 1989. Comparison of the titration and ion adsorption methods for surface charge measurement in oxisols. Soil Sci. Soc. Am. J. 53 1040-1045. 

The results of surface charge measurements of the membranes as a function of pH, pure water fluxes and electronmicrographs are shown in the MF, UF, and NF chapters, respectively. 

Fig. 7. Surface charge measurements vs. displacement on mo different types...

The combination of shifts in EM with surface charge measurements and titration data can be interpreted to provide important information on the surface speciation, which is complimentary to spectroscopic data. Titration data provide information on the net proton or hydroxyl release from the surface. Among the techniques that can be utilized is suspension of the oxide in the background electrolyte, adjustment of the pH to the value of interest, adjustment of the background electrolyte with the adsorbing ion, then mixing the two and measuring the proton or hydroxyl mass necessary to return to the specified pH, in conjunction with determination of the concentration of anion adsorbed. These data are then reported in mol H or OH per mmol anion adsorbed. 

Figure 10.2. Schematic of an experimental set-up used for surface charge measurement...

The surface charge of M"-" is equal to the surface charge of electroinactive Fc, which can be evaluated from the difference in Fc surface charge measured in the presence and absence of Tb +. 

Both linear and cross-linked monodisperse latexes of polystyrene in the size range 0.1 - 1.2y have been prepared by persulfate-initiated emulsion polymerization (6,7,8), and the size and size distributions of the polymer spheres detennined by electron microscopy. Free electrolyte was removed by a mixed-bed ion exchange resin, and surface charge measured by conductometric titration against standard base. Redispersion in organic media was effected by successive dialyses, first with methanol and finally against the desired solvent. 

Additionally electrophoresis was employed to obtain information about the surface charges. Measurements were carried out under conditions of isotachophoresis, but missing a terminating electrolyte, due to the extremely low... 

K. Hu, M. Brust, A. Bard, Characterization and surface charge measurement of self-assembled... 

Surface charge measurements confirmed the presence of negative and positive charges on the surface of hydrogels containing either carboxylic or... 

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