The binding of N,N-dimethyldodecylamine oxide micelles to oppositely charged polyanions of variable charge density, namely sulfonated poly(vinyl alcohol) (PVAS) and random copolymers of 2-(acrylamido)-2-methylpropanesulfonate and acrylamide (P(AMPS-AAm)), was studied using turbidimetry, dynamic light scattering, and potentiometric titration. Complexation occurs at a well-defined critical pH corresponding to a critical micelle surface charge density σ c. The effects of ionic strength I on σc and polyelectrolyte average structural charge density h conform to σc h a ∼ κ b , where κ is the Debye-Hü ckel parameter proportional to I 1/2 . Taken along with previous studies, the results show that the exponent b for cylindrical micelles is larger than that for spherical micelles. The effects of h cannot be explained solely on the basis of average charge spacing but must also take into account the sequence distributions of charged residues.

Monte Carlo simulations were used to investigate the adsorption of a polyelectrolyte chain on an oppositely charged micelle. The influence of the concentration of monovalent salt on the isolated polyelectrolyte chain was investigated by considering the chain expansion factor and persistence length. The polyelectrolytemicelle complex was characterized in terms of the amount of adsorbed polymer in trains, loops, and tails. The overcharging of the complex and the conformation of the adsorbed polyelectrolyte chain was also studied. The ionic strength adsorption-desorption limits were estimated at different micelle charge densities and compared to existing data for the experimental system of sulfonated poly(vinyl alcohol) and micelles of dimethyldodecylamineoxide of varying degrees of protonation. The effect of the relative micelle concentration on the adsorption-desorption limit of the system was also investigated.

Carboxylated ficolls were prepared as model spherical colloids of variable charge and size, with radii ranging from 3.0 to 19.3 nm. Capillary electrophoresis (CE), electrophoretic light scattering (ELS), and potentiometric titration were used to determine mobilities as a function of pH, degree of ionization R, and surface potential ψ 0 . Measured mobilities typically display a plateau at high pH, corresponding to high R and ψ 0 , confirming the general nature of this effect for charged spheres, seen also for charged dendrimers and charged latex particles. This result is examined in the context of a discontinuity in mobility predicted by the Wiersema, O'Brien, and White (WOW) theory and a more recent primitive model electrophoresis (PME) theory, in which bound counterions are considered either as point charges or as hard spheres. While no mobility maximum can be determined as expected by these two theories, our data seem more to support Belloni's theoretical expectations on charged polymers and spheres. Here we explain the mobility plateaus in terms of counterions accumulated close to the surface (surface potential-determining ions) or within the shear plane (mobilitydetermining ions).

Mixed micelles of sodium dodecyl sulfate (SDS) with Triton X-100 (TX100) or dodecyl octa(ethylene glycol) monoether (C12E8) at different bulk SDS mole fractions (Y) and at two ionic strengths were analyzed by frontal analysis continuous capillary electrophoresis. For most systems, the electropherograms showed a distribution of mobilities, providing evidence of compositional heterogeneity in the mixed micelles. From the empirical relationship between average mobility and Y, the mobility distributions may be interpreted in terms of a distribution of micelle compositions. Broad distributions were observed from 0.1 ≤ Y ≤ 0.6 in all cases, while the mixed micelles were close to monodisperse at Y ≥ 0.8. As similar results were obtained from monodisperse C12E8 and polydisperse TX100, the compositional distributions do not result from the compositional polydispersity of the nonionic surfactant. These results were found to be correlated with the composition dependence of the critical micelle concentration of mixed micelles.

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