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 ox ide block copolymers [PE182:(EO)(6)-(PO)(34)(EO)(6) and PE333:(EO)(17)(PO)( 60)(EO)(17)] has been investigated using high sensitivity differential scan ning calorimetry. The thermal data obtained was examined using previously o utlined procedures [I. Patterson, J. Armstrong, B. Chowdhry, S. Leharne, La ngmuir 13 (1997) 2219; B.Z. Chowdhry, M.J. Snowden, S.A. Leharne, J. Phys. Chem. 101(1997) 10226]. These analysis routines have revealed the existence of a small dissociation transition within the thermal envelope of the over all aggregation transition. The transition appears to be associated with th e 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 T-1/2 (the temperature at which the transition is half completed) using dat a obtained for both copolymers, which suggests that the origin of the disso ciation transitions in both copolymers is the same. (C) 2000 Elsevier Scien ce B.V. All rights reserved.