Multiple colloids

Multiple colloids involve the coexistence of three phases, of which two are finely divided, such as multiple emulsions (mayonnaise, milk) of water-in-oil-in-water (w/o/w) or oil-in-water-in-oil (o/w/o). 

Furthermore, there are other instances (multiple colloids) that may involve the co-existence of three phases of which two (and sometimes three) phases are finely divided. One example is a porous solid partially filled with condensed vapour, when both the liquid and vapour phases within the pores are present in a finely divided form a similar situation arises when oil and water co-exist in the pores of an oil-bearing rock, also in frost heaving when water and ice co-exist in a porous medium. Multiple emulsions consist for example of finely divided droplets of an aqueous phase contained within oil droplets, which themselves arc dispersed in an aqueous medium. 

Three-phase colloidal systems (multiple colloids)... 

The examples of colloids listed in Table 10.2 may be considered simple colloids because they involve one fairly distinct type of dispersed and continuous phase. In practice, many colloidal systems are much more complex in that they contain a variety of colloidal types, such as a sol, an emulsion (or multiple emulsions), an association colloid, macromolecular species, plus the continuous phase. Such systems are often referred to as complex or multiple colloids. As we shall see, even the simplest colloids can be quite complex in their characteristics. It should be easy to understand, then, why the difficulty of understanding a multiple colloid increases dramatically with the number of components present. 

In network colloids the definition of colloids in terms of dispersed phase and dispersion medium breaks down since the networks consist of interpenetrating continuous channels. Examples include porous solids, where a solid labyrinth contains a continuous gas phase. There are also examples of colloids where three or more phases coexist, two or more of which can be finely divided. These are called multiple colloids. An example is an oilbearing porous rock, since both oil and water will be present within the solid pores. 

Our main focus in this chapter has been on the applications of the replica Ornstein-Zernike equations designed by Given and Stell [17-19] for quenched-annealed systems. This theory has been shown to yield interesting results for adsorption of a hard sphere fluid mimicking colloidal suspension, for a system of multiple permeable membranes and for a hard sphere fluid in a matrix of chain molecules. Much room remains to explore even simple quenched-annealed models either in the framework of theoretical approaches or by computer simulation. 

This protocol was extended to other inorganic colloids (e.g., ZnS, PbS), and it was pointed out that such extension paves the way to an electrochemical coding technology for the simultaneous detection of multiple DNA targets based on nanocrystal tags with diverse redox potentials [148]. 

In the absence of multiple scattering, the turbidity of a colloidal suspension is given as... 

Solutions of Moiseev s giant Pd colloids [49,161-166] were shown to catalyze a number of reactions in the quasi homogeneous phase, namely oxidative ace-toxylation reactions [162], the oxidative carbonylation of phenol to diphenyl carbonate [166], the hydrogen-transfer reduction of multiple bonds by formic acid [387], the... 

Fig. 4.4 SEM image of a cross section of the beginning of the assembled colloidal crystal film to illustrate the growth of multiple layers. Reprinted from Ref. 15 with permission. 2008 Institute of Electrical and Electronics Engineers...

Visualizing more than one epitope on one section can be accomplished by different fluorescence labeling or different sizes of colloidal gold coupled to primary or secondary antibodies. Primary antibodies from different species and adequate secondary antibodies labeled differently can be used. In case of primary antibodies from the same species, the hapten technique can be applied. A hapten is a small molecule that can be bound to antibodies dinitrophenol and arsinilate are typically used as haptens. Again, adequate secondary antibodies labeled differently can be used (14,17,32). A collection of protocols for multiple immu-nolabeling has been described by Beesley (37). 

Attention was paid early on to solution pH, and in particular, to a surface — bulk proton balance. Various models of hydroxyl chemistry have been developed in colloid science literature [21], Perhaps the simplest and most common model assumes a single type of OH group and amphoteric behavior (i.e., one set of Kx and K2 from Figure 6.1). More complicated models invoke multiple OH groups and proton affinity distributions [22]. It will be demonstrated below that the simpler type has worked well for the revised physical adsorption (RPA) model. 

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