Adsorption density/isotherm

The adsorption of fully and partially hydrolyzed (88%) polyvinyl alcohol (PVA) on 190-1lOOnm monodisperse polystyrene latex particles was investigated. The effect of molecular weight was investigated for 190 nm-size particles using the serum replacement adsorption and desorption methods. The adsorption density at the adsorption-isotherm plateau followed the relationships for the fully hydrolyzed... 

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

Isotherm Subtraction. A second method (7) of determining the net proton coefficient from adsorption data is an adaptation of the thermodynamics of linked functions as applied to the binding of gases to hemoglobin (19). The net proton coefficient determined by this method is designated, Xp- The computational procedure makes a clear distinction between the influence of adsorption density and pH on the magnitude of the net proton coefficient. The fundamental equation used in the calculation of Xp is... 

P=f(Xp. pH). As described above, the magnitude of P is inexorably linked to the variations of x with pH and adsorption density. However, the response of x (and P) to T and pH varies among hydrous oxides. For example, Figure 9a shows the instantaneous (isotherm) proton coefficient (xp) "zones" determined for Cd ion adsorption onto (am)Fe20o O, a-A O and oc-TiC. The zones are defined by the calculated proton coefficients determined for a range of pH values and adsorption density. The "thickness" of each zone gives a qualitative comparison of the pH dependency of Xp at each adsorption... 

Adsorption and ElectroKlnetic Behavior of Rutile. Isotherms for the adsorption of lysine, prollne and glutamic acid on rutile (1102) are given in Figure 1. There is no simple relationship between the adsorption density and the equilibrium concentration. The adsorption does not obey the Langmiur, Freundllch or Stern-Grahame relationships. The leveling-off of the adsorption... 

Adsorption and Electrokinetic Behavior of Hydroxyapatite. The adsorption densities of glutamic acid and lysine on hydroxyapatite are shown in Flgures b and 7. The change in slope of the adsorption isotherm at 10 M glutamic acid is considered to be due to a... 

Adsorption at liquid surfaces can be monitored using the Gibbs adsorption isotherm since the surface energy, y, of a solution can be readily measured. However, for solid substrates, this is not the case, and the adsorption density has to be measured in some other manner. In the present case, the concentration of adsorbate in solution will be monitored. In place of the Gibbs equation, we can use a simple adsorption model based on the mass action approach. 

Fig. 48 Surfactant aggregation numbers determined at various adsorption densities (average number at each adsorption density shown along the adsorption isotherm)...

This is the important Gibbs adsorption isotherm. (Note that for concentrated solutions the activity should be used in this equation.) Experimental measurements of y over a range of concentrations allows us to plot y against Inci and hence obtain Ti, the adsorption density at the surface. The validity of this fundamental equation of adsorption has been proven by comparison with direct adsorption measurements. The method is best applied to liquid/vapour and liquid/liquid interfaces, where surface energies can easily be measured. However, care must be taken to allow equilibrium adsorption of the solute (which may be slow) during measurement. 

C- is also reached in the region cTf conc entratioir 5 CMC (Fig. 7,8). No adsorption isotherms were determined for the flotation experiments shown since we gathered from the data published by Scamehorn et al ( 2), who studied the change of the adsorption density as a function of the composition of binary isomer mixtures of Na-alkylbenzene sulfonates on alumina and kaolinite. 

Figure 7.20. (a) Reflectivity ( ) and Pb La fluorescent-yield (FY) ( ) data and corresponding best fits (solid lines) for Pb(II)-bearing solutions in contact with the a-Al203 (1-102) surface (pH 4.5). (b) Pb adsorption isotherm corresponding to the best-fit adsorption densities from the FY data in Figure 7.20(a) (from [179]). 

Zero Point of Charge. We are operating on the assumption that pH-dependent surface charge arises predominantly from H+ adsorption by reactions of the hydroxylated surface similar to Reactions 1 and 3. Figure 4 shows schematic H+ adsorption isotherms illustrating the pH variation of surface charge and H+ adsorption density, Y/, associated with this source. Curve a represents the total amount of adsorption on a given amount of surface area. Curve b represents more surface. In both... 

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