Dilute solutions of a poly(styrene-b-dimethylsiloxane) diblock copolymer with block molecular weights of 4 and 12 kDa, respectively, were prepared in a series of styrene-selective dialkyl phthalates:  dioctyl phthalate (DOP), dibutyl phthalate (DBP), and diethyl phthalate (DEP). The phthalates were chosen because the interfacial tension between the core block and the solvent can be continuously varied by mixing the solvents in varying proportions. The morphologies were characterized by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). By increasing the selectivity of the mixed solvent at room temperature the equilibrium micelle morphology changed from spheres (DOP) to cylinders (DBP) to vesicles (DEP). The selectivity of the solvent was then reduced by increasing the temperature, and we observed the reverse transitions:  cylinders → spheres (in DBP) and vesicles → cylinders → spheres (in DEP). Since the core block is always above its glass transition temperature (T g ≈ −123 °C), micellar rearrangement was possible within the time scale of the experiment (i.e., minutes). An interesting consequence of these thermotropic transitions is that the viscosity of the solution can be increased upon heating. For example, in the mixed solvent DEP/DBP (1:1), the diblock forms vesicles at room temperature, but when heated, the micelle morphology changes to cylinders and the viscosity of the solution increases by an order of magnitude.

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Small angle neutron scattering was performed on disordered mixtures of nonadsorbing homopolymer (A) chains and diblock (A-B) copolymer micelles in an A selective solvent. Increasing the molecular weight or concentration of A led to an increase in the aggregation number, and a decrease in the effective hard-sphere diameter of the micelles. Furthermore an intermicellar attractive force developed, which was successfully modeled by the Asakura-Oosawa depletion potential. Via an alternative model we also extracted information about mesoscopic clusters of micelles formed due to this attractive force.

A binary solution mixture of distinct block copolymer micelles is found to adopt a superlattice. The larger micelles, formed from polystyrene-polyisoprene diblocks, have a nominal radius of 29 nm; the smaller micelles, formed from polystyrene-polydimethylsiloxane diblocks, have a nominal radius of 16 nm. The superlattice unit cell dimension is 156 nm and is assigned to space group Fm3c; it corresponds to the AB13 structure. As these diblocks are uncharged, the driving force for superlattice formation is primarily free volume entropy, as in sterically stabilized colloidal hard spheres.