Salt Induced Micellization of Ethylene Oxide-Propylene Oxide Block Copolymers in Aqueous Solution

Micellization of three ethylene oxide-propylene oxide block copolymers L43 (EO₆PO₂₁EO₆, mw PPO = 1220, %PEO = 30), PI23 (EO₂₀PO₆₉EO₂₀, mw PPO = 4025, %PEO = 30) and F127 (EO₉₉PO₆₉EO₉₉, mw PPO = 4025, %PEO = 70) in aqueous sodium chloride solution was examined by surface tension, dynamic light scattering and viscosity measurements over the temperature range 30-50°C. Salt induced micellization and micelle growth was observed; the presence of added sodium chloride develops hydrophobicity in the PPO moiety and reduces hydrophilicity of PEO moieties favouring micellization of these block copolymers at relatively lower concentrations than in water at ambient temperature. The results are discussed in terms of CMC, area/molecule, and hydrodynamic size of micelles. Aggregation pattern of copolymers with different molecular characteristics showed similarity but with some marked differences.