Binding of polyelectrolytes to oppositely charged ionic micelles at critical micelle surface charge densities

Abstract

The interaction of ionic/nonionic surfactant micelles with strong polyelectrolytes has been studied by turbidimetric titrations. There exists a critical micellar fraction of ionic head groups, Yc, below which no interactions can be detected. At Y > Yc, the solute components form either soluble aggregates, complex coacervate, or amorphous precipitate, depending, in part, on the polymer:surfactant stoichiometry. The dependence of Yc on the square root of the ionic strength, P/2, appears as a linear phase boundary, which is rather insensitive to polymer concentration or total surfactant concentration. For several polyelectrolyte/mixed-micelle systems, we have measured the surface potential of the micelle ('F0) at values of Y and I corresponding to the polyion-micelle complex formation phase boundary. In the system poly-(dimethyldiallylammonium chloride)/sodium dodecyl sulfate, C12E06, the values of 'P0 measured from the pKt of the probe, dodecanoic acid, are constant (ca. -10.8 mV) along the phase boundary. For the same polymer-surfactant system, \P0 measured with the fluorescence probe hexadecylhydroxycoumarin increases with Yc from -18 to -24 mV along the phase boundary. For the system of reversed charge, sodium polystyrenesulfonate/dodecyldimethylamine oxide, in which the cationic surfactant head group itself acts as a potential probe, the surface potential varies from +12 to +43 mV along the phase boundary. The foregoing results, taken together with the absence of an effect of polymer chain length on Yc, suggest that critical conditions for complex formation are dictated by the cooperative adsorption of a relatively short sequence of polyion segments to the colloid surface. It appears likely that this process occurs when a critical potential is reached at the locus of the closest approach of the polymer chain to the micelle surface. The measured potential at critical conditions increases with the distance between this steric boundary and the mean position of the solubilized probe.

Binding of Polycarboxylic Acids to Cationic Mixed Micelles: Effects of Polymer Counterion Binding and Polyion Charge Distribution

“…3. In the presence of TMAC, we find the same linear dependence of Y c on I 1/ 2 as revealed in previous studies on a number of polyelectrolyte-micelle systems (9,11,53). This linearity suggests that the phenomenon is governed by Eq.…”

Effects of Polyelectrolyte Chain Stiffness, Charge Mobility, and Charge Sequences on Binding to Proteins and Micelles

“…An important consequence of theory 8,9 is the finding of a transition from bound to unbound state with a change in any of those three variables, so that the critical conditions for binding at constant temperature could be expressed as a result initially obtained for polyelectrolyte adsorption onto flat surfaces, but subsequently found for spherical colloids as well, 9,10 with values of b ranging from 0.5 to 3. [8][9][10][11] This result has been supported by experiments with various polyelectrolytes interacting with oppositely charged micelles [12][13][14][15][16][17] and large dendrimers (smaller dendrimers behaving more like large counterions). 14,18 Still, discrepancies between the experimental systems and the theoretical model must be noted.…”

Coacervation in Biopolymers

“…In summary, the interactions basically reduce to that between a PE and a PA. It has been observed that due to heterogeneous charge distribution found on protein surface, polyions (polyanions or polycations) selectively bind to oppositely charged surface patches of protein molecules through electrostatic interaction overcoming the repulsive interaction occurring between similarly charged surface patch and the polyion [62,67,[71][72][73]. Thus, SPB has been largely observed in protein-PE based interactions.…”