Self-assembly of poly(ethylene oxide)-poly (propylene oxide)-polyethylene triblock terpolymer amphiphiles

We review here the self-assembly of poly(ethylene oxide)-poly(propylene oxide)-polyethylene (EO_jPO_nC_i) triblock terpolymers in aqueous solution, and discuss it in the light of micellization of similar nonionic amphiphiles, alkyl-ethoxylates (C_iEO_j) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers (EO_jPO_nEO_j). The role of PPO block in the self-assembly of EO_jPO_nC_i amphiphiles is discussed for both dilute and concentrated aqueous solutions. In dilute aqueous solution, the free energy contribution of PPO to micellization, ΔG(PO), is found not to favor the self-assembly of EO_jPO_nC_i (i.e., PPO is relatively hydrophilic). In concentrated aqueous solution, EO_jPO_nC_i amphiphiles form lyotropic liquid crystalline phases. In these phases the role of the PPO block is assessed from drying data. The PPO block in concentrated aqueous phases is relatively hydrophobic. The underpinnings of this graded phase behavior are examined as a function of composition of the amphiphile and temperature.