Molecular structure and ionic strength both affect the micellization and solubilization behavior of PEO-PPO-PEO surfactants

In this paper, the influence of the molecular structure of poly(ethylene oxide)-poly(propylene oxide)-poly (ethylene oxide) block copolymer surfactants (poloxamers or pluronics) on their micellization and solubilization behavior was studied. From density measurements, an inverse relationship between the critical micelle temperature (CMT) and the molecular weight of the propylene oxide part was observed, whereas a higher ethylene oxide content increased the CMT of a pluronic solution. Besides the molecular structure of the surfactant, the ionic strength of the aqueous solution largely affected the CMT. Within the concentration range studied, a linear decrease of the CMT with increasing ionic strength was observed. Experiments with the hydrophobic dye quinizarin confirmed that the solubilisation behaviour of pluronic surfactants at a fixed temperature could be largely affected by the electrolyte present.