Particle Micelle Stabilization

The stabilization of a micelle can be aehieved by two distinctly different mechanisms depending upon whether the molecules involved are able to 

1 Charge Stabilization Derjaguin-Landau-Verivey-Overbeek (DLVO) Theory 

For the Stern model xJ/q is replaced by ij/i, to allow for the effect of contact charges on the shape of the potential. 

Where V otal and 8Ftotai/8 both equal zero, the stabilizing barrier disappears and we get flocculation. Thus 

However, K = ncQe z lEkT) and therefore cq= lOVa Insert- 

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Soap. A critical ingredient for emulsion polymerization is the soap (qv), which performs a number of key roles, including production of oil (monomer) in water emulsion, provision of the loci for polymerization (micelle), stabilization of the latex particle, and impartation of characteristics to the finished polymer. 

When soft colloids (such as stars, block copolymer micelles, or particles sterically stabilized with grafted chains) are suspended in solvents of intermediate quality at high concentrations, an increase of temperature leads to an increase of their effective volume fraction, which in turn can yield vitrification [26,190,199]. A representative example is depicted in Fig. 23a for a star with nominal / = 128 and... 

Hanaoka et al.were able to control the Rh particle to a similar size of 4-4.2 nm. In our case, by increasing our water/surfactant ratio to 70, an average size of 9.75 nm Pd particle with 16% metal loading was obtained (Table 1). Thus, our results agree with the observations that diameter of metal nanoparticles synthesized inside the micelle system depends on micelle diameter (the included material < the aqueous core) which critically depends on water/surfactant ratio used. The subsequent application of the silica-gel coating onto these micelle stabilized metal nanoparticle does not seem to seriously alter... 

A foam is a dispersion of a gas in a liquid or a solid. The formation of foam relies on the surface activity of the surfactants, polymers, proteins, and colloidal particles to stabilize the interface. Thus, the foamability increases with increasing surfactant concentration up to critical micelle concentration because above critical micelle concentration, the unimer concentration in the bulk r ains nearly constant. The structure and molecular architecture of the foam is known to influence foam-ability and its stability. The packing properties at the interface are not excellent for very hydrophilic or very hydrophobic drug. The surfactant promoting a small spontaneous curvature at interface is ideal for foams. Nonionic surfactants are the most commonly used one. The main advantage with foams is its site-specific delivery and multiple dosing of the drug. ... 

The problem of particle nucleation was first addressed in the 1980s by Candau and coworkers [14,104] for the case of water-in-oil microemulsions. Their studies concerned the polymerization of acrylamide inside water-swollen micelles stabilized by AOT and dispersed in toluene. A thorough investigation of the structures prior to and after polymerization by elastic and quasi-elastic light scattering (QELS), viscomelry, and ultracentrifugation experiments yielded two key experimental results ... 

It is well known that water-soluble surfactants tend to form various types of aggregates at threshold values above the CMC. This aggregation process is the result of two competing factors. The hydrophobic chains try to avoid the energetically unfavourable contact with water. This can be achieved by forming various types of defined aggregates (micelles). These particles are stabilized by van der Waals attractions between the... 

Emulsion polymerizations have also been performed in supercritical CO2. Here the monomer is CO2 insoluble (or only slightly soluble) but the initiator is CO2 soluble. Most of the monomer is dispersed as droplets in the CO2 that are stabilized by surfactant molecules adsorbed to the surface. Micelles are also present in emulsion polymerizations. The initiator is soluble in the CO2 phase but not in the monomer droplet, and thus the micelles act as the meeting place for the monomer and initiator. The systems contains three types of particles micelles where polymerization is not occurring, micelles where polymerization is occurring (called the polymer particle), and monomer droplets (Fig. 12). 

Figure C2.3.11 Key surfactant stmctures (not to scale) in emulsion polymerization micelles containing monomer and oligomer, growing polymer particle stabilized by surfactant and an emulsion droplet of monomer (reservoir) also coated with surfactant. Adapted from figure 4-1 in [67],...

Most synthetic latices contain 5—10 wt % of nonelastomeric components, of which more than half is an emulsifier or mixture of emulsifiers. One reason for this relatively high emulsifier concentration as compared with natural latex is that emulsifier micelles containing solubiHzed monomer play a principle role in the polymerization process. A high emulsifier concentration is usually necessary to achieve a sufficiently rapid rate of polymerization. Secondly, a considerable fraction of the surface of the polymer particles must be covered by adsorbed soap or equivalent stabilizer to prevent flocculation... 

Asphalt emulsions are dispersioas of asphalt ia water that are stabilized iato micelles with either an anionic or cationic surfactant. To manufacture an emulsion, hot asphalt is mixed with water and surfactant ia a coUoid mill that produces very small particles of asphalt oa the order of 3 p.m. These small particles of asphalt are preveated from agglomerating iato larger particles by a coatiag of water that is held ia place by the surfactant. If the asphalt particles agglomerate, they could settle out of the emulsion. The decision on whether a cationic or anionic surfactant is used depends on the appHcation. Cationic stabilized emulsions are broken, ie, have the asphalt settle out, by contact with metal or siHcate materials as weU as by evaporation of the water. Siace most rocks are siHcate-based materials, cationic emulsions are commonly used for subbase stabilization and other similar appHcations. In contrast, anionic emulsions only set or break by water evaporation thus an anionic emulsion would be used to make a cold patch compound. 

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