title: A Vesicle-to-Worm Transition Provides a New High-Temperature Oil Thickening Mechanism.
abstract: Diblock copolymer vesicles are prepared via RAFT dispersion polymerization directly in mineral oil. Such vesicles undergo a vesicle-to-worm transition on heating to 150 °C, as judged by TEM and SAXS. Variable-temperature1H NMR spectroscopy indicates that this transition is the result of surface plasticization of the membrane-forming block by hot solvent, effectively increasing the volume fraction of the stabilizer block and so reducing the packing parameter for the copolymer chains. The rheological behavior of a 10 % w/w copolymer dispersion in mineral oil is strongly temperature-dependent: the storage modulus increases by five orders of magnitude on heating above the critical gelation temperature of 135 °C, as the non-interacting vesicles are converted into weakly interacting worms. SAXS studies indicate that, on average, three worms are formed per vesicle. Such vesicle-to-worm transitions offer an interesting new mechanism for the high-temperature thickening of oils.
authors.affiliation: Dainton Building, Department of Chemistry, The University of Sheffield, Sheffield, South Yorkshire, S3 7HF, UK.
authors.forename: Matthew J
authors.identifier: 0000-0001-5010-6725
authors.initials: MJ
authors.lastname: Derry
authors.affiliation: Dainton Building, Department of Chemistry, The University of Sheffield, Sheffield, South Yorkshire, S3 7HF, UK.
authors.forename: Oleksandr O
authors.identifier: 0000-0003-4110-8328
authors.initials: OO
authors.lastname: Mykhaylyk
authors.affiliation: Dainton Building, Department of Chemistry, The University of Sheffield, Sheffield, South Yorkshire, S3 7HF, UK.
authors.forename: Steven P
authors.identifier: 0000-0002-8289-6351
authors.initials: SP
authors.lastname: Armes
keywords: RAFT polymerization; block copolymers; morphology transition; nanoparticles; polymerization-induced self-assembly