Origins, colloid stability

Two kinds of barriers are important for two-phase emulsions the electric double layer and stcrie repulsion from adsorbed polymers. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stability that is called DLVO, after its originators Deijaguin, Landau. Vervcy, and Overbeek. The theory provided substantial progress in the understanding of colloidal stability, and Its treatment dominated the colloid science literature lor several decades,... 

Polyacrylic acid stabilised latices have been prepared by aqueous dispersion polymerisation. The method used is analogous to the non-aqueous dispersion (NAD) polymerisation methods originally used to prepare polymethyl methacrylate particles in aliphatic hydrocarbons (1. In effect the components of a NAD polymerisation have been replaced as follows aliphatic hydrocarbon by aqueous alcohol, and degraded rubber, the stabiliser, by polyacrylic acid (PAA). The effect of various parameters on the particle size and surface charge density of the latices is described together with details of their colloidal stability in the presence of added electrolyte. 

There are very important phenomena originated when a polymer is on one interface or close to one interface. Such phenomena include adsorption, adhesion, monolayer formation, coating and colloidal stabilization. In the majority of circumstances a polymer adsorbed onto colloidal particles will increase the stability of a dispersion [8], The essential feature of polymer or steric stabilization is... 

According to the aggregative and coagulative nucleation mechanisms which have been derived originally from the homogeneous nucleation theory of Fitch and Tsai [128], the most important point in the reaction is the instant at which colloidally stabilized particles form. After this point, coagulation between similar-sized particles no longer occurs, and the number of particles present in the reaction is constant. As shown in Fig. 6, the dispersion copolymerization with macromonomers is considered to proceed as follows. (1) Before polymerization, the monomer, macromonomer, and initiator dissolve completely into the... 

Interaction between double layers, one of the building bricks of colloid stability, is an important theme planned for Volume IV. It has a large number of spin-offs, in, for instance ion exchange, thin wetting films, free films, membranes, association colloids, vesicles, polyelectroljdes, emulsions and rheology. The dramatic influence of electroljrtes on these phenomena finds its origin in the changes in the double layer, discussed in this chapter. 

Let us consider the colloidal stability of particles as ones view moves from a mountain spring to a river, through an estuaiy, and into the ocean. Solid particles and natural organic matter are everywhere in aquatic environments. Here we consider that NOM adsorbs on particles and affects their colloidal stability. We discuss the origins of this stability a long the riverrun (I). Our conclusions are based on results with both mathematical and laboratory chemicals (2). Speculation is extensive. 

In this case, as indicated above, the colloid stability is controlled by the form of the interaction free-energy curve as a function of particle separation. The DLVO theory in its original form considers just two contributions to this energy, namely the attractive van der Waals potential and the repulsive potential that arises when the diffuse double layers round the two particles overlap. To put this in a quantitative form we need to examine more closely the origin of the curves shown in Figures 3.6 and 3.7. 

The principles of colloid stability, particularly including DLVO theory and steric stabilization, can be applied to many food emulsions [80,81]. The applicability of DLVO theory is restricted, however, partly because the primary potential-energy minima are somewhat shallow and partly due to the tendency of adsorbed proteins extend outward from surfaces so far that steric stabilization becomes more important [34,126]. The presence of protein in an adsorption layer can also contribute a viscoelastic restriction to coalescence. Finally, the oils in food colloids are usually triglycerides (of either animal or vegetable origin). These oils may exist in liquid or crystalline states at room temperature frequently both simultaneously. The existence of the crystal form at interfaces contributes yet another stabilizing component [34]. 

Clarke et al. (36) later explored the possibility of an electrical doublelayer contributing to the repulsion, thereby assisting in the stabilization of the film thickness. This double-layer repulsion is identical in origin to that in the DLVO theory of colloid stability (Chapter 4). Assuming that the grains have flat, parallel faces separated by a distance h, the expression for the doublelayer repulsion is... 

Our work is mainly focused on colloidal PEC particles, which are prepared by mixing polycation and polyanion solutions in nonstoichiometric ratios [10-15], and on exploring their potential to interact in a useful manner with pharmaceutically and biomedically relevant compounds. The main issues of our research are reproducibility in the preparation protocol, uniformity of size and shape, conservation of colloidal stability after binding of compounds and the interaction with surfaces. In typical PEC systems, standard cationic and anionic PELs and PELs of natural origin (e.g., polypeptides, polysaccharides, and their modified analogues) are combined. 

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