Polymer-micelle complexes mixed micelles

KEISHIRO SHIRAHAMA is Professor of physical chemistry of St a University, Saga, Japan. He received a doctor of science from Kyushu University. His academic interest is directed to amphiphilic molecular assemblies such as surfactant-polymer complex, mixed micelle, and vesicle as well as random phenomena in physicochemical systems. 

Li Y, Dubin PL, Havel HA, Edwards SH, Dautzenberg H. Electrophoretic light-scattering, dynamic light-scattering, and turbidimetry studies of the effect of polymer concentration on complex-formation between polyelectrolyte and oppositely charged mixed micelles. Macromolecules 1995 28 3098-3102. 

Zhen Z, Thung CH. Interaction of sodium carboxymethylamylose with aqueous surfactants in both the presence and the absence of added salt mixed micelles and inclusion complexes. Polymer 1992 33 812-816. 

In this contribution, we describe our recent experimental and theoretical findings on complex coacervate core micelles. We have investigated the co-assembly of several types of oppositely charged ionic-hydrophilic block copolymers into mixed micelles. In particular, we have focused on chain mixing/segregation in the micellar corona as a function of monomer type and (the ratio between the) chain length of the polymer blocks in the corona. Our aim has been to employ co-assembly in such systems as a route towards formation of reversible Janus micelles. These are micelles with a corona that exhibits two distinguishable sides (hemispheres in the case... 

The micro-structure of the surfactant aggregates in the polymer complex can be considered as that of micelles with a hydrophobic core inside, with some segments of the polymer chain being also involved in the aggregate. Evidence for this structure has been given by NMR measurements. The combination of the polymer segments with the surfactant aggregate is likely to be similar to mixed micelles, i.e. the... 

The raising of the cloud point of a nonionic surfactant by an anionic surfactant can be considered to be a special case of polymer/surfactant interaction. Here the polymer is a hydrophobically substituted species in which the hydrophilic moiety with repeating units (most often ethylene oxide) is an oligomer rather than a tme polymer. This phenomenon has been of much importance, and has long been known, to formulation chemists and involves the close association of the two species in mixed micelles—the complexes in this case. 

Another interesting system is based on the adsorption of so-called complex coacervate core micelles (also called polyion complex micelles) [28,29]. These micelles are formed in aqueous solution when two oppositely charged polyelectrolytes are mixed, with at least one of these polyelectrolytes being connected to an uncharged and water-soluble polymer. The complexed polyelectrolytes then form the complex coacervate core of the micelles, while the neutral chain forms the corona. These micelles have been shown to adsorb to surfaces with very different properties, such as silica and polystyrene. Although formed brushes are of low density, good antifouling properties have been observed [28,30]. 

For present purposes, solubilization is defined as a spontaneous process leading to a thermodynamically stable, isotropic solution of a substance (the additive) normally insoluble or only slightly soluble in a given solvent produced by the addition of one or more amphiphilic compounds, including polymers, at or above their critical micelle concentration. Using such a definition, we can cover a broad area that includes both dilute and concentrated surfactant solutions, aqueous and nonaqueous solvents, all classes of surfactants and additives, and the effects of complex interactions such as mixed micelle formation. It does not, however, limit the phenomenon to any single mechanism of action. 

The cac concept is less useful when considering the association between hydrophobicaUy modified (HM) polyelectrolytes and surfactants. The reason is that the HM polyelectrolytes themselves associate and form hydrophobic microdomains into which added surfactants can be incorporated [30], a process akin to mixed micelle formation [31]. Hence, even at low concentrations the surfactants added to the polymer solution can be incorporated in the hydrophobic microdomains present. A consequence of this is that pol5uner-surfactant complexation occurs over a broader range of surfactant concentration and it is difficult to determine a critical concentration. 

A new insight into the dynamic processes in the bulk and at the surface of surfactant solutions can be seen in molecular dynamics simulations. Only now are computers sufficiently powerful that such simulations can be performed without too many simplifications. The state of the art of molecular dynamics was recently summarised by van Os Karabomi (1993), showing that complex processes such as micelle formation (Karabomi O Connell 1993), emulsion formation or solubilisation processes (Smit et al. 1993) can be simulated. Future improvements of computers and algorithms will provide a deep insight into even more complex processes connected with dynamics of interfacial phenomena, such as adsorption layer stracture and formation, effects of molecular interfacial and bulk interactions in mixed systems of surfactants and polymers. 

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