Abstract : Block copolymers of styrene and methacrylic acid dissolved in water/ dioxane mixtures form spherical micelles with polystyrene cores and poly(methacrylic acid) shells. When two micellar solutions containing micelles made from two different copolymers are mixed, the micelles may hybridize. The hybridization was followed by the method of sedimentation velocity. The rate of hybridization was found to be a very sensitive function of the architecture of both copolymers and of the thermodynamic properties of the solvent mixture. In many instances this rate is imperceptible slow; it may be totally frozen when the solvent is very poor with respect to the micellar core. The analysis of the hybridization of numerous micellar pairs provided new insights into the dynamics and thermodynamics of unimer/micelle equilibria. (Author)