Polymeric micelles minimum micelle concentration

Table 4.8. Synthesis of azo groups-containing polyacrylamides by precipitation polymerization in tert-butyl Alcohol and the surface activity of the products. CMC = critical micelle Concentration, omm = minimum surface tension...

Schick and Fowkes (11) studied the effect of alkyl chain length of surfactants on critical micelle concentration (CMC). The maximum lowering of CMC occurred when both the anionic and nonionic surfactants had the same chain length. It was also reported that the coefficient of friction between polymeric surfaces reaches a minimum as the chain length of paraffinic oils approached that of stearic acid (12). In order to delineate the effect of chain length of fatty acids on lubrication, the scuff load was measured by Cameron and Crouch (13). The maximum scuff load was observed when both hydrocarbon oil and fatty acid had the same chain length. Similar results of the effect of chain length compatibility on dielectric absorption, surface viscosity and rust prevention have been reported in the literature (14-16). 

When emulsifiers, such as soaps, alkyl sulfates, and alkyl sulfonates, are present in water above a minimum concentration called the critical micelle concentration, the emulsifier molecules aggregate into micelles. In micelles, the hydrophobic ends of the emulsifier are clustered at its center, and the hydrophilic ends extend into the aqueous phase. Micelles are spherical or lamellar with dimensions on the order of 2.5 to 5 nm, depending on the emulsifier used. There may be 10 to 10 micelles/cm of water. When monomer initially is added, a small fraction of the molecules is absorbed into the micelles, swelling them slightly. Most of the monomer is dispersed as droplets 1000 to 3000 nm in diameter, stabilized with emulsifier molecules along their surface. They number about 10 ° to 10 particles/cm of water. These droplets serve as the monomer reservoir for the polymerization. A representation of emulsion polymerization early in the process is shown in Fig. 19.14. 

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