Electrostatic stabilization mechanism

Solubilization of insoluble oxidation products and soot particles. Reverse micelles (RMs) formations manage the prevention of agglomeration and the contamination process of insoluble oxidation particles and soot particles by both steric stabilization (Fig.2.1) and electrostatic stabilization mechanisms (Fig.2.2). The steric stabilization mechanism provides a physical barrier to agglomeration of particles by adsorption on particle surfaces. Adsorbed dispersant acts as a physical barrier to attraction between particles. 

Fig. 2.2. Electrostatic stabilization mechanism by proton transfer (/w OH+s) or by hydrogen bonding complex formation (AAAAO...HA), where SH is a strong acid, e.g., sulfuric acid, and HA represents an organic acid...

These types of magnetic fluids, owing to the strongly polar character of the carrier, have several particularities concerning their preparation procedures, as well as their colloidal stability and physical properties. The doublelayer electrostatic stabilization mechanism [9] gives weakly stable and relatively low concentration magnetic fluids, which manifest phase-separation (droplike... 

In the common procedure extremely large oil-water interfacial area is generated and the particle nuclei grow in size with the progress of the polymerization. Thus, effective stabilizers such as ionic and non-ionic surfactants and protective colloids e.g. hydroxyethyl cellulose and polyvinyl alcohol), which can be physically adsorbed or chemically incorporated onto the particle surface, are often required to prevent the interactive latex particles from coagulation. Under the circumstances, satisfactory colloidal stability can be achieved via the electrostatic stabilization mechanism [268], the steric stabilization mechanism [269] or both. 

Inversion emulsion polymerization involves the dispersion and then polymerization of hydrophilic monomers, normally in aqueous solution, in a nonaque-ous continuous phase. The emulsifier systems primarily based on the steric stabilization mechanism (see Section 1.3.3) are quite different from those of the more conventional oil-in-water emulsion polymerization processes. This is simply because the electrostatic stabilization mechanism (see Section 1.3.2) is not effective in stabilizing inverse emulsion polymerization comprising an aqueous disperse phase and a nonaqueous continuous phase with a very low dielectric constant. The unique anionic surfactant bis(2-ethylhexyl) sulfosuc-cinate (trade name Aerosol OT) that can be dissolved in both oil and water... 

In addition to the electrostatic stabilization mechanism, latex particles can be stabilized by adsorption of hydrophilic polymer chains on their particle surfaces. The physically adsorbed or chemically grafted polymer chains surrounding the colloidal particles and extending themselves into the continuous aqueous phase serve as a steric barrier against the close approach of the pair of particles. In this manner, coagulation of latex particles can be prevented via the steric stabilization mechanism [17,18]. Typical nonionic surfactants and surface-active, nonionic block copolymers are quite effective in imparting such a steric stabilization effect to colloidal dispersions. 

The electrostatic stabilization mechanism is well documented for simple OfW emulsions (Myers, 1998a). Multiple emulsion droplets are much larger in size, and therefore the repulsive electrostatic forces are less pronounced (Figure 5.5). 

The reactions depicted in Fig. 32 are most often carried out at low temperatures. The incursion of a thermal process at elevated temperatures has occasionally been observed. In some cases the thermal oxygenation products are identical to the photochemical products and in other cases are different. For example, when 2,3-dimethyl-2-butene/02 NaY is warmed above — 20 °C a reaction was observed which led to pinacolone (3,3-dimethyl-2-butanone) as the major product.98,110 Pin-acolone is not formed in the photochemical reaction at the same temperature. On the other hand, identical products were observed in the thermal and photochemical intrazeolite oxygenations of cyclohexane.114,133 135 These intrazeolite thermal processes occur at temperatures well below that necessary to induce a classical autooxidation process in solution. Consequently, the strong electrostatic stabilization of oxygen CT complexes may also play a role in the thermal oxygenations. Indeed, the increase in reactivity of the thermal oxygenation of cyclohexane with increasing intrazeolite electrostatic field led to the conclusion that initiation of both the thermal and photochemically activated processes occur by the same CT mechanism.134 Identical kinetic isotope effects (kH/kD — 5.5+0.2) for the thermal and photochemical processes appears to support this conclusion.133... 

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