Micellar networks, formation

A. Bernheim-Groswasser, E. Wachtel, and Y. Talmon. Micellar growth, network formation, and criticality in aqueous solutions of the nonionic surfactant C12E5. Langmuir, 16(9)4131 1140, 2000. 

Formation and disruption of viscoelastic wormlike micellar networks in the mixed-surfactant systems of sucrose alkanoate and polyoxyethylene alkylether. J. Phys. Chem. B., 108, 14009-14015. 

Koh, H.-D., Changez, M., Rahman, M.S., and Lee, J.-S. (2009) Formation of intermicellar-chained and cylindrical micellar networks from an amphiphilic rod-coil block copolymer poly(n-hexyl isocyanate)-WocA-poly(2-vinyl-pyridine). Langmuir, 25,7188-7192. 

Two system-dependent interpretative pictures have been proposed to rationalize this percolative behavior. One attributes percolation to the formation of a bicontinuous structure [270,271], and the other it to the formation of very large, transient aggregates of reversed micelles [249,263,272], In both cases, percolation leads to the formation of a network (static or dynamic) extending over all the system and able to enhance mass, momentum, and charge transport through the system. This network could arise from an increase in the intermicellar interactions or for topological reasons. Then all the variations of external parameters, such as temperature and micellar concentration leading to an extensive intermicellar connectivity, are expected to induce percolation [273]. 

In sodium bis(2-ethylhexyl) phosphate microemulsions, which are composed of cylindrical micelles in the dilute region, it has been observed that the formation of micellar clusters is characterized by a branched structure as the volume fraction (<1>) of the aggregates increases. At d> > 0.2, these clusters mutually overlap, forming a network expanded overall [283]. 

The formation of such structures was attributed to short-range attractive forces arising from transient fluctuations in the periphery of the corona, leading at times to attractive interactions between micelles. These aggregated states, i.e., strings and networks, were observed whenever the added salt concentration was increased. Further increase of salt concentration eventually led to very large networks and macrophase separation into a dilute micellar phase and a concentrated gel phase [15]. 

Fig. 11 Schematic view of a possible mechanism for the formation of micellar and filament networks. Different states of association are shown as function of intermicellar distance r...

The formation of filaments, filament networks, and micellar strings is schematically shown in Fig. 11 as a function of the intermicellar distance r. Upon collisions small repulsive interactions are overcome to overlap adjacent micellar shells to form a shared ion cloud. The disruption of strings leads to the formation of filaments which can lead to a filament network. Further increase of intermicellar distance disrupts filament connections to form single micelles. 

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