Identification and deconvolution of dissociation and aggregation transitions during thermally induced micellisation in aqueous solutions of ethylene oxide–propylene oxide–ethylene oxide block copolymers

The aggregation behaviour of two ethylene oxide–propylene oxide–ethylene oxide block copolymers [PE182:(EO)6(PO)34(EO)6 and PE333:(EO)17(PO)60(EO)17] has been investigated using high sensitivity differential scanning calorimetry. The thermal data obtained was examined using previously outlined procedures [I. Patterson, J. Armstrong, B. Chowdhry, S. Leharne, Langmuir 13 (1997) 2219; B.Z. Chowdhry, M.J. Snowden, S.A. Leharne, J. Phys. Chem. 101 (1997) 10226]. These data analysis routines have revealed the existence of a small dissociation transition within the thermal envelope of the overall aggregation transition. The transition appears to be associated with the thermally induced break-up of large aggregates and occurs simultaneously with or slightly before the micellar aggregation of the block copolymers. A reasonable linear relationship exists between the van’t Hoff enthalpy and T1/2 (the temperature at which the transition is half completed) using the data obtained for both copolymers, which suggests that the origin of the dissociation transitions in both copolymers is the same.