Micellar solutions of associative triblock copolymers: Entropic attractionand gas-liquid transition

We report the first clear observations of an entropy-driven phase transitio n between a dilute micellar "gas" and a disordered but highly associated mi cellar "liquid" realized with aqueous solutions of poly(ethylene oxide) cha ins fully end-capped with C-16 and C-18 hydrophobes. Dynamic light scatteri ng and capillary viscometry determine the radii and aggregation numbers of the micelles and, together with the coexisting concentrations, permit estim ates of the strength of the entropic attraction through the adhesive hard-s phere model. The behavior is qualitatively consistent with expectations for the entropy gain from the exchange of end blocks between cores of flowerli ke micelles consisting of associative triblock copolymers.