Heterocoagulation

This phenomenon is quite general and has a number of important practical applications. 

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Relaxations in the double layers between two interacting particles can retard aggregation rates and cause them to be independent of particle size [101-103]. Discrepancies between theoretical predictions and experimental observations of heterocoagulation between polymer latices, silica particles, and ceria particles [104] have promptetl Mati-jevic and co-workers to propose that the charge on these particles may not be uniformly distributed over the surface [105, 106]. Similar behavior has been seen in the heterocoagulation of cationic and anionic polymer latices [107]. 

Heterocoagulation Heterocyclic Heterocyclic amines Heterocyclic azo dyes Heterocyclic compounds Heterocyclic dyes Heterocyclic polymers Heterocyclic thiophenes Heteroepitaxy Heterogeneous catalysis Heterogemte Heteroglycan Heterojunction... 

Adler, P.M., 1981. Heterocoagulation in shear flow. Journal of Colloid and Interface Science, 83, 106-115. 

As in the case of rosin sizing, the first step is to retain the emulsified size particle in the wet web. The mechanism of retention is probably by heterocoagulation of the cationic size particles to the negatively charged fibre surface. The charge characteristics of the stabilising polymer become important as demonstrated by the effect of pH on the retention of AKD emulsion particles stabilised with a tertiary cationic starch (Figure 7.17). 

Hansen, F.K. Matijevic, F. (1980) Heterocoagulation. Part 5. Adsorption of carboxylated polymer latex on monodispersed metal hydrated oxides. J. Chem. Soc. Faraday Trans. I. 76 1240-1262... 

In principle, the coating may be produced in two ways, i.e., by (1) interacting the cores with preformed smaller particles of a different composition (essentially by heterocoagulation), and (2) by forming the shell directly by chemical reaction on preformed particles dispersed in salt solutions yielding the coating. In both instances it is essential that conditions be optimized in order to avoid having mixed dispersions of coated and constituent particles. 

A good discussion of this may be found in Hunter (1987, Chapter 6). It is, however, helpful to list some expressions for interactions between dissimilar spherical particles since they are useful in studying heterocoagulation problems. Hogg et al. (1966) and Wiese and Healy (1970) have derived the following equations for spherical particles for low surface potentials and thin double layers ... 

Table 8.2 shows the signs of KR that accord with equations (8.1) and (8.2) for different homocoagulation and heterocoagulation situations, (n.b. Attraction is negative and repulsion positive.)... 

Tombacz, E., Gilde, M., Abraham, I. and Szanto, F. (1990). The possibihty of heterocoagulation between montmorillonite and humic substances, Appl. Clay Sci. 5,265-270. 

Thus mixing of latices containing particles of opposing charge can lead to coagulation and this phenomena is usually termed HETEROCOAGULATION. 

Figure 15. Scanning electron micrograph illustrating the heterocoagulation of cationic latex particles (diameter = 0.43 fj/n) onto a negatively charged latex particle (diameter = 2.14 pm)...

D. C. Prieve and E. Ruckenstein, Role of surface chemistry in primary and secondary coagulation and heterocoagulation, J. Colloid Interface Sci. 73 539 (1980). 

Solid-solid interface Adhesion Flocculation Heterocoagulation Sedimentation... 

Colloidal Semiconductors in Systems for the Sacrificial Photolysis of Water. 1. Preparation of a Pt/Ti02 Catalyst by Heterocoagulation and its Physical Characterization 254... 

Anderson who considered dumbbell shaped particles for which theory was derived and experiments carried out. The test particles were doublets of two latex spheres, one negative, the other positive (and different in size) that were formed from the singlets by heterocoagulation. For parallel and perpendicular orientation of the doublets with respect to E the following equations could be derived... 

Measurements of heterocoagulation can be made in much the same way as were measurements for the addition of an electrolyte to a latex. For example, with an appropriate mixing device (Cheung, 1979) an anionic latex can be added to a cationic one and the progress followed by turbidity measurements to obtain a stability ratio. Results of this type are shown m Fig. 24 in the form of log W against Af /(Af+ + N ) where N+ and are the number concentrations of the cationic and anionic lattices respectively. The anionic latex used was composed of polystyrene particles (diameter... 

Many publications are devoted to adsorption of surfactants, proteins and polymers on latexes, but adsorption of inorganic ions on latexes does not seem to be very active field. Latexes are also used as model colloids in studies of heterocoagulation, i.e, adsorption of colloids on colloids. 

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