Interaction between star-like block copolymer and sodium oleate in aqueous solutions

The interaction between a star-like block copolymer (AP432) and an anionic surfactant sodium oleate (C17H33COONa) was investigated in detail both at the air/water interface and in bulk aqueous solutions. The results of surface tension show that AP432 and C17H33COONa could form mixed micelles. The results obtained from the oscillating barrier measurements at low dilational frequencies (0.01–0.1 Hz) reveal that the maximum values of the dilational modulus for AP432/C17H33COONa mixed system moved to lower concentrations compared to those of single AP432 or C17H33COONa aqueous solutions. Steady-state fluorescence measurements indicate that after mixing, the I1/I3 values of AP432/C17H33COONa system above the cmc are higher than those of single AP432 or C17H33COONa solutions. This is probably due to a looser pack of the molecules within micelles for the AP432/C17H33COONa mixture, which is also consistent with the results obtained from TEM observations. For comparison, the interaction between a commercially available linear PEO–PPO–PEO copolymer (Pluronics L64) and C17H33COONa was also studied. All experimental results give clear evidence that the interaction between L64 and C17H33COONa is different from that between AP432 and C17H33COONa.