Aggregation of telechelic triblock copolymers: From animals to flowers

We present an experimental study of dilute solutions of a polystyrene-polyisoprene-polystyrene block copolymer in a bad solvent of the polystyrene terminal blocks (heptane). At high temperature, it was previously shown that these copolymers associate in polydisperse and loose aggregates having a small association number and a large radius of gyration. These aggregates have been called ''animals''. Here, we deal with the change of the aggregate structure as the solvent selectivity is increased. Actually, scattering experiments show an aggregate compaction as the temperature is decreased. They pass from an ''animal'' to a ''flowerlike'' structure with a dense core and a swollen corona. However, small angle neutron scattering proves that these flowerlike micelles are always linked together. In addition, to account for this compaction, we present the study of a diblock copolymer, corresponding to roughly half of the triblock, and measurements of the solubility of homopolystyrene in heptane. This allows us to quantify the different terms of the free energy per chain in the aggregates, from which one perceives how the temperature tunes the balance of interfacial tension and conformational entropy leading to different aggregates conformations.