Aggregation and clouding behavior of aqueous solution of EO–PO block copolymer in presence of n-alkanols

Abstract

The aqueous solution behavior of an ethylene oxide–propylene oxide triblock copolymer Pluronic ® P123 [(EO) 20(PO) 70(EO) 20] was investigated in the presence of various n-alkanols (C 1–C 6) by cloud-point, viscosity, dynamic light scattering (DLS) and spectroscopic (FTIR, NMR) measurements. For lower alkanols (methanol, ethanol and 1-propanol), the cloud-points (CPs) increased with increase in alkanol concentration. The reverse effect was found for higher alkanols (C 4–C 6) where both the CPs and critical micelle temperatures (CMTs) decreased with increase in concentration. This behavior is explained in terms of a co-operative association of higher alkanols and block copolymers by replacing water molecules in the PPO core and inducing micellar growth in aqueous P123 solution. Lower alkanols are likely to be good solvents for both PEO and PPO blocks and the effect on PPO blocks predominates indicating an increase in CP and CMT with increase in alkanol concentration.