Surface amphoteric

Because the latex soHds ia the saturatioa process are deposited ia the stmture of the paper web by dryiag, the coUoidal system is aot as critical as with beater additioa. Noaioaic and amphoteric surface-active materials can be effectively used ia the latices. A low surface teasioa and small particle size are desirable features. 

The incorporation of metal salts of amphoteric surface active agents (Mostat Series) as internal antistatic agents in polypropylene fibers has been reported (95). Metal salts of alanine, amidoamine, and imida2oiine-type amphoteric surface-active agents show excellent performance as internal antistatic agents and also improve the dyeing abiUty of the fibers with acid dyes. 

The measurement of the surface potential asa function of pH for an oxide provides valuable information for the determination of the parameters which describe the surface reactions. Ionizable surface site theories of the formation of surface charge and potential at an oxide surface in contact with a liquid electrolyte involve many more parameters than can be directly experimentally determined. Additional assumptions are required to evaluate these parameters, which explains why there is often no agreement in the literature about their value. A mathematical treatment of the amphoteric surface site model is given which exhibits the characteristic quantities which can be experimentally measured. It is shown that the measurement of both the surface potential i/>o and the surface charge 00 are required to completely determine these characteristic quantities. This approach is applied to Si02 and AI2O3, two surfaces for which both charge and potential measurements are available. 

In a typical inorganic oxide, the oxide surface acquires a charge by the dissociation or adsorption of potential determining ions at specific amphoteric surface groups or sites. As a consequence the equation of state of such surfaces will involve parameters that characterize surface reactions. In addition, one may also allow for the adsorption of anions and cations of the supporting electrolyte. However, in this paper we shall ignore this possibility to keep the discussion clear. Such embellishments of the model of the surface do not alter the key ideas presented here. 

We derive the equation of state of an amphoteric surface by considering the generic dissociation reactions involving potential determining ions ... 

Figure 1. The charge-potential curves layer and an amphoteric surface where...

Figure 2. The charge-potential curves for a Gouy-Chapman diffuse layer and an amphoteric surface 10 1 1 electrolyte, ApK = 2, N = 1 X 1018 nf2.

Detailed numerical examples of the behaviour of the surface charge and surface potential when the electrical double layer of two identical amphoteric surfaces overlap and interact are available in the literature (8). Examples of the differences between the form of the interaction free energy under constant... 

Using a simple amphoteric model for the mineral surface, we have demonstrated the role specific chemical binding reactions of potential determining Ions In determining the electrical properties and thermodynamics of the oxide/solution interfaces. A by-product of our study Is that under appropriate conditions, an amphoteric surface can show marked deviations from ideal Nernstlan behaviour. The graphical method also serves to Illustrate the... 

The dependences of pH and C-potential on the adsorbed amount of M(H20)2+ at the total metal ion concentrations of 3 x10-3 mol dm-3 are shown in Figures 7 and 8, respectively. The amount adsorbed for each M2+ increases with the pH, and the inflection points are shifted toward the lower pH region in the order of Co2+, Zn2+, Pb2+, Cu2+, which corresponds to the order of the hydrolysis constant of metal ions. To explain the M2+-adsorption/desorption, Hachiya et al. (16,17) modified the treatment of the computer simulation developed by Davis et al. (4). In this model, M2+ binds coordina-tively to amphoteric surface hydroxyl groups. The equilibrium constants are expressed as... 

A field effect transistor (FET) measures the conductance of a semiconductor as a function of an electrical field perpendicular to the gate oxide surface (13). When the gate oxide contacts an aqueous solution a change of pH will change the SiOj surface potential p. A site-dissociation model describes the signal transduction, a function of the state of ionization of the amphoteric surface SiOH groups (14). Typical pH responses measured with SiO ISFETs are 37-40 mV/pH unit (15). 

The chemical literature and patent art disclose a great variety of amphoteric surface active molecules. The author has attempted to address only those that are of economic importance today. Not all of the current commercial products fall into the categories above, so a few additional ones are mentioned here. 

Such calculations were first performed by Ninham and Parsegian (1) for the case of two identical plane, acidic surfaces. Later, Pricve and Ruckenstein (2, 3) and Chan et al. (4, 5) independently published numerical results of similar calculations for the case of two identical, plane, amphoteric surfaces. Rates of hydrosol adsorption were calculated by Prieve and Ruckenstein (6), who used the double-layer interaction between the particle and collector corresponding to identical and acidic or amphoteric surfaces. However, in a real situation the particle and collector surfaces are different. 

Fig. 1. Interaction of two surfaces having of different magnitude, bul the same sign = —20 or —10 mV). Note sign changes in both charge and force. A — 20 is a strong acid-like surface, whereas B - 20 is a buffer-like amphoteric surface. For other details, see Table I.

Another limiting case is the interaction of two amphoteric surfaces with a high buffer capacity. In the case that the surfaces are identical, it was observed above that [Pg.122]

On the other hand, if the amphoteric surfaces are not identical rr0 + a, still tends to zero, but computations show that o-0 and (T tend to become equal and large in magnitude and opposite in sign. Then the osmotic pressure term in Eq, [4] remains bounded, but the Maxwell stress can overwhelm the repulsive contribution (as in Eq. [5]) so that ... 

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