Polymer-bound micelles

Small angle scattering experiments confirm that the polymer-bound micelles form distinct necklaces (12). Figure 4 shows the scattering curves of micelles bound to a FEO of M - 1.35E5. Here the shoulder corresponds to a separation between bridged micelles, with a low coordination number and a separation d 3 diameters. 

B. Surfactant Exchange from Polymer-Bound Micelles... 

The next studies involved kinetic and binding studies and used PVP or PEO and various alkylsulfate surfac-tants. The value of kVN was found to be independent of the polymer concentration and molecrdar weight and to be rather close to those in the absence of polymer when taking into account the smaller value of N for the pol3rmer-boimd micelles, as compared to free micelles. The association of a surfactant with a polymer-bound micelle was formd to be diffusion-controlled. ... 

The study of the lithium perfluorononanoate/PVP system by NMR showed separate resonance hnes corresponding to free and polymer-bound micelles at These lines coa-... 

Apparent Critical Micelle Concentration (cmc) and Aggregation Number for Polymer-Bound Micelles. 

These aggregation numbers for the polymer-bound micelles are much larger than the munbers of surfactant units per polymer chain (Table 1). Therefore, it is evident that micelles are formed firom associations of the surfactant moieties not only on the same polymer chain but also on different polymer chains. For example, in the case of the copolymer of m = 6 with... 

The first pathway is the formation of mixed micelles or hemimicelles, composed of polymer-bound hydrophobes comicellized with surfactant molecules. Intermolecular physical cross-links often enhance the viscosity of the micellar solutions. The second pathway is intramolecular comicellization so that the hydrodynamic size of the associates contracts. 

In the presence of the polyelectrolyte ordinary CPC micelles also appear somewhat above the cmc for pine surfactant [16,34,42]. This is seen from the d>v values, which above 1 X 10 3 mol dm 3 tend to the absolute values for the apparent molar volume of CPC incorporated in micelles. For comparison, below cmc the apparent molar volume of CPC is approximately constant (around 342 cm3 mol1) above cmc, at surfactant concentration equal to 0.01 M, it reaches 367 cm3 mol-1. In polyelectrolyte solutions at the same surfactant concentration, the maximum surfactant micelles prevail in solution over the polymer-bound ones. 

Because of their chemical similarity, the polymer-bound hydrophobes have a tendency to interact with the hydrophobic part of the surfactant molecule. If the surfactant concentration in the system is high enough, micelles are formed. If there are enough micelles in the system, then all the hydrophobes will get bound to micelles (Figure 14). As a result, there will be no intermolecular hydrophobic association (Figure 2) and no viscosity... 

The solubilization of the HMHEC in the surfactant was attributed to the interactions between surfactant micelles and polymer-bound hydrophobes. The effect of pH on polymer-surfactant solution viscosity was explained in terms of charge effects at the surface of the surfactant micelles. Steiner (13) proposed that at pH levels above or below the isoelectric point, the surfactant has a net charge on the head groups that causes repulsion within a single micelle. This repulsion leads to a relatively open micelle-aqueous phase interface through which polymer-bound hydrophobes can enter and experience stable polymer-surfactant interactions. These interactions anchor the polymer chains in an extended configuration. 

On the other hand, the trans configuration of fumarate ions and rigidity of benzenetetracarboxylate ions do not allow them to interact simultaneously with two surfactant head groups on a single micelle. In the presence of these ions, polymer-bound hydrophobes penetrate more readily into the micelles. In addition, these counterions can potentially bridge two or more micelles, and further stabilize the solution. 

Thus, K-casein in its native stabilizing role exists, probably as small disulphide linked polymers, bound to the micellar surface (the ill-defined boundary between the hydrophobic interior of the micelle and the aqueous phase). C-terminal polypeptides (61 residues) of the protein project from the surface into the solution. In this position, the macropeptide moiety of the protein is conformationally free (H), constrained only by its interactions with its neighbours (J ), and the bond 105-106 of the protein is held in a particularly advantageous position for attack by enzymes such as chymosin ( ). The importance of this will be apparent when emulsions stabilized by K-casein are being discussed. The enzymic action has a relatively small but detectable effect on the hydrodynamic diameters of the particles, and a large effect on their electrophoretic mobilities, which decrease by between one-third and one-half, depending on the solution conditions ( ). 

Hydrophobic ally modified ionic hydrogels formed in oppositely charged surfactant solutions exhibit frequency-dependent dynamic moduli if they are in equilibrium in water after extraction of free surfactant micelles. This is a result of complex formation between the ionic polymer and the oppositely charged surfactant, leading to polymer-bound surfactant counterions in the hydrogels. 

Free or immobilized enzymes have been exploited already in a number of systems. Here, biocatalysis may take place in reversed micelles or in an aqueous phase in eontaet with an organic solvent. In a powdered state some enzymes are able to funetion in pure organic solvents. Furthermore, modified enzymes such as polymer bound enzymes or surfactant-coated enzymes have been developed so that they ean solubilize in organie solvents to overcome diffusion limitation. The advantages of enzymatie reaetions using organic solvents can be briefly summarized as follows ... 

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