The solubilization of a oils of varying polarity in block copolymer micelles was studied for the case of triblock ethylene oxide / propylene oxide polymers (Pluronics, PEO-PPO-PEO), polyisobutylene-b-polymethacrylic acid (PIB-PMAA), and polybutadiene-b-polystyrene-b-polyethylene oxide (PB-PS-PEO). As solubilisates aliphatic and aromatic oils, esters, triglycerides, and alcohols were employed. For the case of the Pluronics pronounced effects on the critical micellisation temperature (cmt) are observed, where the aggregational state was studied by means of fluorescence spectroscopy, dynamic light scattering, and small-angle neutron scattering (SANS). The shift of the cmt to lower temperatures is not only directly related to the amount of solubilised material but also strongly correlated with the type of solubilisate, especially its polarity. From the change of the cmt as a function of concentration thermodynamic parameters such as enthalpy and entropy of micellisation were calculated and correlated with the type of solubilisate employed. The enthalpy of micellisation becomes less endothermic by the presence of solubilisate and this effect is more pronounced for more polar solubilisates. The structure of the formed aggregates was determined in detail by SANS measurements and a systematic correlation between the type of solubilised oil and the aggregate size and structure are drawn. Depending on the polarity of the solubilised oil the oils are located in various regions of the block copolymer micelles.

Still more interesting is the case of the triblock terpolymer PS-PB-PEO / PB-PS-PEO. This polymer forms spherical micelles which contain two different regions in the hydrophobic core. Accordingly one has two different solubilization sites within the micellar core. Depending on the oil added it becomes either solubilised in the center of the core or in the shell region. As that also affects the packing parameter of the system this can lead to a solubilisate induced sphere-to-rod transition or simply to a swelling of the shell. In general, it is observed that blockcopolymer micelles are much more selective with respect to their solubilization properties compared to conventional surfactants.