W. N. Lacey Lectureship in Chemical Engineering

Block copolymers belong to a broad class of amphiphilic compounds that includes soaps, lipids and nonionic surfactants.  These macromolecules assemble into micelles with molecular dimensions on the order of 5 to 50 nm in size when mixed with excess solvent that preferentially solvates one block type.  This presentation will explore two different aspects of block copolymer micelle formation.  The fundamental thermodynamic and kinetic factors that control micelle shape and dynamics will be discussed based on small-angle x-ray and neutron scattering (SAXS and SANS) experiments and cryogenic transmission and scanning electron microscopy results.  Although the structural features displayed by amphiphilic block copolymers resemble those associated with the self assembly of lipids and simple surfactants (e.g., spherical and cylindrical micelles and vesicles), a macromolecular architecture leads to remarkably different dynamic properties, linked to a vanishingly small critical micelle concentration.  As a consequence, molecular exchange is rapidly extinguished with increasing molecular weight resulting in non-ergotic behavior.  These concepts have been exploited in developing a recently commercialized technology that provides immense improvements in the fracture toughness of thermosetting epoxy plastics, which will also be discussed.