Amphiphilic block copolymer self-assembly in solvent mixtures: Solvent quality effects on formation of micelles

Amphiphilic block copolymers of the poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) family (commercially available as Pluronics or Poloxamers) are well-known for self-assembling in water (selective solvent for PEO) into micelles with a PPO-rich core and a hydrated PEO corona. The association of amphiphiles is of great fundamental interest to pharmaceutical applications. The effect of added polar organic solvent on the micellization of PEO-PPO block copolymers was assessed by studying the critical micellization concentration (cmc) in ternary isothermal (25°C) systems of pharmaceutical interest consisting of Pluronic F127, water and ethanol. Addition of ethanol to water disfavors the formation of micelles, i.e., the water-ethanol mixture provides better solvent conditions for the block copolymer than water. Addition of 20% v/v ethanol doubled the cmc of the PEO-PPO block copolymer.