  We present a model for the joint self-assembly of amphiphilic polymers and
small amphiphilic molecules (surfactants) in a dilute aqueous solution. The
polymer is assumed to consist of a hydrophilic backbone and a large number of
hydrophobic side groups. Preference of the surfactant to bind to hydrophobic
microdomains along the polymer induces an effective attraction between bound
surfactants. This leads to two distinct binding regimes depending on a single
physical parameter, \epsilon, which represents the ratio between
surfactant-polymer affinity and polymer hydrophobicity. For small \epsilon the
binding is non-cooperative, whereas for large \epsilon it becomes strongly
cooperative at a well-defined critical aggregation concentration. Our findings
are in accord with observations on diverse experimental systems.
