Critical micelle condensation

Segregation of a poly(2-vinylpyrrolidone- /oc -styrene-c/8- /oc -2-vinylpyrrolidone) (PVP-dPS-PVP) triblock and dPS-PVP diblock copol5miers between the PS and PVP homopolymers was studied by Dai and co-workers (169). Both the block copolymers show an increase in the interfacial excess beyond the saturation plateau, due to condensation of copolymer micelles adjacent to the PS/PVP interface in the PS phase (Fig. 9). A significantly lower critical micelle condensation (CMC) was determined for the triblock copolymer when compared with the diblock. While the condensation of the diblock copolymer micelles at the PS/PVP surface occurs above the CMC, no such preferential segregation is observed for the triblock copolymer. 

This methodology enjoys the merits of other approaches and exhibits several additional advantages 1) it has proven applicable to a wide range of transition metal and main group oxides 2) the metal precursors studied so far are readily available, being either alkoxide or halide complexes 3) in many cases, syntheses can be run in alcoholic solvents in essentially nonhydrolytic conditions, which aids in controlling hydrolysis and condensation rates 4) the critical micelle concentrations required for polyethylene-oxide-polypropylene-oxide di- and triblock copolymers are usually much lower than the concentrations needed for ionic surfactants and 5) because of the neutral, nonaqueous conditions used in these preparations, control of pH is not required, and the surfactant can be removed from the mesostructured material by calcination or milder solvent extraction methods with nonpolar solvents. 

The interfacial tension between CO2 and various condensed phases including water [63], styrene oligomers[64] and polyethylene glycol[8] has been measured with a tandem variable-volume tensiometer and modeled with gradient theory. Also surfactants were added to these systems to lower the interfacial tension and to determine the surfactant adsorption. A critical micelle concentration was observed for... 

In a recent study, the influence of indifferent electrolytes on the adsorption behaviour of cationic soluble surfactant solutions has been investigated by surface tension measurements, ellipsometry and surface second harmonic generation (SHG). ° Each technique addresses different structural aspects and the combined data provide a detailed picture of the interfacial architecture. The analysis gives an indirect proof of the existence of a phase transition between the free and condensed state of the counterions caused by a small increase of surface charge close to the critical micelle concentration (cmc). 

In this chapter, we shall be concerned with dilute solutions of surfactants in water, in the absence of oil. Above a certain concentration (the critical micellar concentration), which is generally very low, amphiphilic molecules spontaneously self-assemble to form small aggregates called micelles. As in the case of microemulsions, the spontaneous structuring of the mixture arranges all polar heads so that they are in contact with water, for which they have strong affinity. The hydrophobic tails, brought together into a condensed liquid state in the core of the object, thereby minimise contact with the aqueous solvent. 

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