The onset of soluble complex formation between polycations and nonionic/anionic mixed micelles was found to occur at well-defined micelle surface charge density, sigma(o), which could be modulated via Y, the mole fraction of anionic surfactant in the mixed micelle. Critical values of Y were detected by precision turbidimetry for two polycations, each combined with any of the four mixed micelles formed from two anionic and two nonionic surfactants. The values of Y-c observed for each of the resultant eight ternary polycation/anionic-nonionic combinations were used as surrogates for polycation binding affinity: for a given polycation and a given value of Y, micelles with Y-c < Y will bind, while those with Y-c > Y will not. The polycation affinity of micelles correlated with their "zeta potential" (zeta), measured by electrophoretic light scattering, and their average surface potentials (Psi(0)), measured by potentiometric titration of a comicellized probe. For a given polycation at a fixed ionic strength, we found that the critical zeta potential (zeta(c)) measured at Y-c was independent of the surfactant pair chosen. This potential at the micelle "shear plane" is thus interpreted as the potential experienced by a bound polycation. The binding affinity was furthermore found to be stronger for polycations with higher linear charge density as well as for micelles with higher axial ratio, attributed respectively to an increase in the number of micelle-bound charged polycation repeat units and to the higher surface potential for micelles with lower surface curvature.