Amphoteric latex particles

The limitations of the traditional Poisson-Boltzmann treatment are numerous. A particularly important one refers to specific ion effects. The amphoteric latex particles coagulate when the concentration of CsN03 is approximately 1 M, but remain stable at high pH values even when the concentration of KN03 exceeds 3 M [6]. Nevertheless, in the traditional Poisson-Boltzmann approach the double layer repulsions for Cs and K are the same. A number of attempts were made to include additional interactions in the formalism, some of them being briefly discussed in the first part of this article [7], With these corrections, many of them dependent on unknown parameters, the modified Poisson-Boltzmann approach regained its explanatory power, and in general most of the experiments could be accounted for... 

The hydration force is important for distances between plates less than a few nanometers. Since the DLVO potential barrier between spherical particles or droplets is located at separation distances of the order of the Debye length, it is clear that at least at high electrolyte concentrations the hydration force becomes relevant. The qualitative effect of hydration was earlier recognized, regarding the stability of silica colloids at high electrolyte concentrations1 or the stability of amphoteric latex particles at high concentrations of some electrolytes.12... 

In what follows, one considers for illustration purposes the case in which the charge is generated on the surface of colloidal particles or droplets by the adsorption of a surfactant, namely sodium dodecyl sulfate (SDS). We selected this case because information about the adsorption of SDS on an interface is available in the literature, and as it will become clearer later the number of parameters involved is smaller than in the case of silica. A more complex calculation about the silica and the amphoteric latex particles will be presented in a forthcoming paper. It involves several kinds of surface dipoles and equilibrium constants. 

With formaldehyde and amines such as dimethylamine, diethylamine, or pentaethylenehexamine, Mannich reactions have been carried out on poly(sty-rene-co-acrylamide) latex particles. The expected tertiary amines were accompanied by hydrolysis products. Thus both the Hofmann rearrangement and the Mamiich reactions led to amphoteric latex particles. When attempts were made to alkylate the Maimich reaction product, soluble products (presumably quarternary ammoniitm salts) were formed. 

Chem CS, Lee CK, Chang CJ (2004) Electrostatic interactions between amphoteric latex particles and proteins. Colloid Polym Sci 283 257-264... 

Furusawa and Anzai investigated the heterocoagulation of a highly monodisperse amphoteric polymer latex (particle diameter 250 nm, lEP ca. pH 6.8 in 5.0 mM KCl background electrolyte, positively charged at low pH) onto various silica spheres (diameters 240, 460, 960, and 1590nm lEP ca. pH 3.0) dispersed in pure water or upon addition of various hydroxypropyl celluloses (HPCs) [17, 18]. Stable dispersions for both individual particles under the condition that they had opposite... 

Fig. 1 Left, (a-d) Different morphologies of heterocoagulate particles that can be obtained when the relative sizes of the two colloids are varied. Right Micrographs obtained from heterocoagulation of an amphoteric latex (diameter 250 nm) at pH 5.6, at which it has a cationic surface charge, with negatively charged silica particles of various diameters 1590 (a), 960 (b), 460 (c), and 240 (d) nm. Reproduced from Figs. 2 and 3 from [17]...

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. 

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