Oppositely charged colloids

Bronich, T.K., Nehls, A, Eisenberg, A, Kabanov, V.A. and Kabanov, A.V. (1999) Novel drug delivery systems based on the complexes of block ionomers and surfactants of opposite charge. Colloids Surf. B, 16, 243-251. 

The addition of polymers can also destabilize a colloidal solution for two reasons. Firstly, when polymers adsorb on more than one colloid and this phenomenon is called bridging. Secondly, when polyelectrolytes neutralize oppositely charged colloids and thereby reduce the electrostatic repulsion between the colloids. In some cases both a destabilization and a stabilization of a solution is desired. One example is the manufacturing of paints, where it is required that the paint is easy to apply on the wall and that it stays on the wall. This can be achieved with a solvent which stabilizes the solution but rapidly evaporates when the paint is applied and makes it possible for the colloidal particles to coagulate. 

Dispersion-flocculation processes are generally controlled by double layer swelling, adsorbed hydrolyzed Fe or Al, and chemical bridging (tactoid formation) (Stumm and O Melia, 1968). Once dispersed, clay colloids are kept dispersed by repulsive double layers (Van Olphen, 1971). The force of repulsion is related to the thickness of the double layer (see Chapter 4). This dimension is represented by the ions concentrated near the oppositely charged colloid surface. Any colloid that has a net negative or a net positive charge repulses a like-charged colloid. 

The colloid, as usually prepared, is electro-positive in character, and may be precipitated from solution by electrolysis, by the addition of small quantities of electrolytes, or by the action of an oppositely charged colloid, such, for example, as (negative) arsemous sulphide, whereby the two electrical charges neutralise each other.7 The smallest quantities of a few electrolytes required to precipitate colloidal ferric hydroxide from solution are given in the following table —8... 

Coagulation of colloids is brought about not only by the effect of electrolytes but also by the interaction of oppositely charged colloids, which sets in when one colloid is adsorbed on the surface of another. The necessary condition for mutual coagulation is equality of opposite charges of the particles of the sol, as a result of which coagulation can occur only in a narrow zone of concentration ratios (Kul skiy, 1960). 

It has been established experimentally that whereas mutual coagulation takes place in certain quantitative relationships when various oppositely charged colloidal systems—hydrophile and hydrophobe—interact, quite a different process can take place in the case of other interrelationships the addition of a small amount of a hydrophile colloid to a hydrophobe system... 

Goddard G D 1986 Poiymer-surfaotant interaotion. Part 2. Poiymer and surfaotant of opposite charge Colloid Surf. 19 301-22... 

The attraction between oppositely charged colloids can be understood and modeled using the DLVO theory [3-6]. The DLVO theory links the van der Waals attraction between particles with the electrostatic effects resulting from the presence of a double layer of counterions. A detailed theoretical discussion lies outside the scope of this chapter. One of the difficulties of the DLVO theory is that an exact analytical description of interaction of overlapping double layers is only known for flat, infinite parallel surfaces. For spherical double layers, approximations need to be made or numerical theoretical simulations need to be performed. 

Lagueerr, A. and Stoll, S. (2005). Adsorption of a weakly charged polymer on an oppositely charged colloidal particle Monte Carlo simulations investigation. Polymer, 46, 1359-1372. 

The said apparent equivalent weights play a great part in complex coacervation of oppositely charged colloids, and explains for instance the shift in optimal mixing ratios by altering the pH (see p. 322, 6b and p. 359, chapter X, 2i). 

The absence of flocculation or coacervation phenomena in a mixture of oppositely charged colloids does not necessarily mean that colloid-colloid interaction is lacking. In mixtures of gum arabic and gelatin at lower pH values (e.g., pH 1.73 — 2.3) no coacervation occurs. Still interaction is present, for in Fig. 43 (p. 324) the curve continues its normal course in this pH range, absolutely different from that in Fig. 50 (p. 332), where the curve ends vertically at 100 % N. Thus in the sol mixture soluble combinations of gelatin and gum arabic are present and they are preferentially absorbed on the carborundum particles, which were used to measure the reversal of charge in these clear sol mixtures. 

Complex Coacervation. The process of coacervation when caused by the interaction of oppositely charged colloids. 

W. Lin, M. Kobayashi, M. Skaiba, C. Mu, P. Galletto, M. Borkovec, Heteroaggregation in binary mixtures of oppositely charged colloidal particles. Langmuir 22(3), 1038-1047 (2006). doiilO. 1021/la0522808... 

Fortini, A., Hynninen, A.P., and Dijkstra, M. Gas-hquid phase separation in oppositely charged colloids Stability and interfacial tension. 2006. 7. Chem. Phys.125 094502. 

Goddard, E. (1986a). Polymer-surfactant interaction part 11. Polymer and surfactant of opposite charge. Colloids and Surfaces 19(2) 301-329. 

Behavior of solutions of oppositely charged polymers is rather similar to that of solutions of oppositely charged colloids. However, higher flexibility of the polymer chains results in a less ordered structure of the polyion solutions. Pairing of the oppositely charged polyions, their aggregation, and complexation of anionic and... 

Puertas A, Femandez-Barbero A, De las Nieves F (2000) Aggregation between oppositely charged colloidal particles. In Buckin V (ed) Trends in colloid and interface science XTV. Progress in colloid and polymer science, vol 115. Springer, Berlin, pp 55-58... 

The second method is the opposite of the first that is to say, the potassium bromide solution is in the buret and is added to the solution of silver nitrate. The phenomena are quite analogous, but the hydrosols differ in one important particular. In the first case as long as the halide ion is in excess of the silver, the ultramicrons are charged negatively, while in the second case where the silver ion is in excess the ultramicrons are charged positively. The two halide hydro-sols mutually precipitate each other, as is to be expected from a mixture of oppositely charged colloids. 

There are four types of encapsulation utilizing the system of phase separation from aqueous solution [127] (i) Complex coacervation or pheise separation resulting from two oppositely charged colloids neutralizing one another, (ii) Simple coacervation where a nonelectrolyte such as alcohol causes formation of a separate polymer-rich phase, (iii) Salt coacervation where a polymer separates eis a result of a salting-out process, (iv) Precipitation and insolubilization of a polymer by changing the pH of the aqueous solution system. 

Crystal Structures of Oppositely Charged Colloids with Size Ratio 0.31. 175... 

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