Stability of the colloidal suspensions

In another application, the magnitude of the zeta potential is measured as a function of added counterions. The variation in zeta potential is found to be related to the stability of the colloidal suspension. The results of a gold colloidal suspension (gold solute) are reported as follows ... 

It is noteworthy that each particle is covered at the end of synthesis both by the hydrophilic fragment resulting from decomposition of the initiator, e.g. sulphate groups, and by the surfactant. Both entities participate in the stability of the colloidal suspension. Emulsion polymerisation of a hydrophobic monomer in aqueous medium is sometimes referred as oil-in-water (o/w), whereas emulsion polymerisation of a hydrophilic monomer, e.g. an acrylamide, in a non-polar organic solvent is referred to as inverse emulsion polymerisation or water-in-oil (w/o). More details about the use of nanospheres for drug delivery can be found in Section 4.4.6. 

Treating cellulose fibers with sulfuric acid involves esterification of hydroxyl groups by sulfate ions (Yao, 1999). Introduction of sulfate groups along the surface of the crystallites will result in a negative charge of the surface. This anionic stabilization via the attraction/repulsion forces of the electrical double layers at the crystallites is probably the reason for the stability of the colloidal suspensions of flie crystallites (Marchessault et al., 1961). The stable aqueous nanocellulose suspension is shown in Figure 1.1(a). 

Finally, these aqueous colloidal solutions were used as catalysts for the hydrogenation of simple olefins and arenes with Roucoux et al. [107], These nanocatalysts appeared efficient in mild conditions, evidencing that these materials are active despite the evolution of their environment related to their dissolution into water. For example, octene and dodecene were fully converted into the corresponding alkanes (r.t 1 bar H2) with moderate activities. An increase in the hydrogen pressure (P(H2) = 10 bar) was not detrimental for the stability of the colloidal suspension. The complete hydrogenation of toluene into cyclohexane was observed overnight with Ru/PTA, whereas 60% of /n-methoxymethylcyclohexane was formed from methoxymethylanisole. Nevertheless, preliminary recycling tests showed that an improvement of the stability and recovery of these materials was necessary to increase their interest in catalysis. 

The DLVO (Derjaguin-Landau-Verwey-Overbeek) theory describes the stability of a colloidal suspension as mainly dependent on the distance between the particles... 

Foam properties related to salt. The addition of sodium chloride to soybean protein suspensions caused them to form high-capacity, low-stability foams (13). It was suggested that foam capacity increased because salt improved protein solubility at the interface of the colloidal suspension during foam formation, but retarded the partial denaturation of the surface polypeptides of proteins that are necessary for protein-protein interaction and stability. 

Any of the particle sols prepared above may be used to adsorb macromolecules to create gold probes. To concentrate the suspensions, the solutions may be filtered through a small-pore filter. Centrifugation also may be done. Each protein-gold complexation should be optimized for the proper amount of protein to add to maintain stability of the colloid. This can be done according to the method described in Section 1. 

Table 6.3. Factors affecting the stability of soil colloidal suspensions...

The magnitude of the zeta potential provides an indication of the potential stability of the colloidal system. If all of the particles in suspension have a large nega-... 

In experimental practice, the stability of a colloidal suspension is frequently evaluated by its (visible) sedimentation behaviour. This is mainly because the settling... 

In many papers, the stability of dense colloidal suspensions is evaluated via the yield stress r o the absence of a measurable yield stress is then interpreted as the absence of significant aggregation. Such an approach is mainly used in parameter studies, when the pH value, the salt concentration, or the dose of some additive is varied (e.g. Franks et al. 1999 Breyer and Sonnefeld 2004). Last but not least, there are various applications in which the onset of gelation has to be accurately detected (e.g. during cheese making). This can be monitored by commercial probes that use torsional or transversal low-frequency vibrations (O Callaghan et al. 2000 Williams et al. 2001). 

The following paragraphs discuss the interdependency between particles and solvent properties and the effect of interfacial changes on selected examples. Again, they deal with pyrogenic powders, which are composed of colloidal aggregates with nanosized primary particles (i.e. the specific surface is relatively large). The stability of multicomponent colloidal suspensions will be discussed in the next Sect. (5.2.6). 

---