Temperature and salt-induced micellization of some block copolymers in aqueous solution

Micellization of three commercial samples of ethylene oxide (EO)-propylene oxide (PO) (PEO-PPO-PEO) triblock copolymers (pluronics) P65 (EO25PO30EO25, mw PPO = 1750, %PEO = 50), P85 (EO25PO40EO25, mw PPO = 2250, %PEO = 50), a nd F88 (EO102PO40EO102, mw PPO = 2250, %PEO = 80) in aqueous sodium chlorid e solution (0-3 M) was examined by cloud point, surface tension, dye spectr al change, fluorescence, and viscosity measurements over a temperature rang e of 25-50 degrees C. Salt-induced micellization and micelle growth were ob served. The presence of sodium chloride enhanced hydrophobicity in the PPO moiety and reduced hydrophilicity of PEO moieties, favoring micellization a t relatively lower concentrations than in water at ambient temperature. The effect of salt on micellization is similar to that of increasing temperatu re. The critical micelle concentrations (CMC) and critical micelle temperat ures showed a marked decrease in the presence of added salt. CMC obtained b y different methods were in good agreement.