Effect of an amphiphilic diol (Surfynol ®) on the micellar characteristics of PEO–PPO–PEO block copolymers in aqueous solutions

Abstract

The aggregation and clouding behaviors of a series of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers, PEO–PPO–PEO (Pluronic ®) containing ethylene oxide (EO) content 30% (P103 and P123), 40% (P84), 50% (P85) and 70% (F87 and F127) in the presence of an amphiphilic diol (C 14diol or Surfynol ®104) were investigated using cloud point, viscometry, dynamic light scattering (DLS) and small angle neutron scattering (SANS). DLS and SANS data reveal micellar growth/transition in the presence of diol; such changes strongly dependant on the EO content and hence on the hydrophilic lipophilic balance (HLB) value of the copolymer. Copolymer with low HLB value showed noticeable growth in the micellar size as compared to one with high HLB. P123 and P103, the least hydrophilic (HLB ∼ 8/9) among the copolymers studied here, show a series of structural changes with the addition of Surfynol. Highly temperature sensitive microstructures and hence the rheological behavior were also observed in P103. These structural changes in micelles are explained in terms of the hydrophobic interaction between the copolymer and diol. The observed results correlate well with the reported HLB values of the block copolymer.