Christelle Lefebvre

Université de Rennes 1, Roazhon, Brittany, France

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Publications (5)20.75 Total impact

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    ABSTRACT: The morphology of micelles formed from linear and cyclic poly(styrene-b-isoprene) copolymers (PS166-b-PI278) has been studied in solvents with different selectivity for the two block components: heptane and decane, good solvents for the PI block, and DMF, a good solvent for the PS block. Using small and ultra small angle X-ray scattering experiments, SAXS and USAXS, respectively, morphological changes were monitored as a function of the temperature. While micelles formed in DMF were stable and no morphological changes occurred as a function of the temperature, transformations from cylinder-like micelles to vesicles-like objects were observed in both decane and heptane above 60 °C for the linear PS-b-PI copolymer. The transition occurred through intermediate steps, where the coexistence between different micellar morphologies was observed. On the contrary, the morphology of the block copolymers with the cyclic architecture was found to be independent of temperature and concentration. For linear blocks, a demicellization was detected at higher temperatures (above 80 °C) and the process was fully reversible when the solution was cooled down to ambient temperature. These results are consistent with complementary dynamic light scattering (DLS) observations.
    Full-text · Article · Feb 2009 · Soft Matter
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    ABSTRACT: Linear poly(styrene-b-vinylmethylether) (PS-b-PVME) has been synthesized using anionic (PS block) and cationic (PVME block) polymerization [1]. The copolymer was first dissolved in THF, a good solvent for both blocks, and water, a selective solvent of the PVME block, was slowly added. Care was taken to operate at a temperature below the low critical solution temperature (LCST) of PVME in water (about 30°C). The copolymer chains self-assembled and formed micelles. Solutions at concentrations from 0.2 to 1 mg/mL were observed by cryo-transmission electron microscopy (cryo-TEM) using a Philips CM200 ‘Cryo’ microscope [1].
    No preview · Article · Jan 2008
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    Michel Schappacher · Jean Luc Putaux · Christelle Lefebvre · Alain Deffieux
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    ABSTRACT: The synthesis, characteristics, and properties of amphipatic, water-soluble dendrigrafts, with a polystyrene core and polystyrene-b-poly(methyl vinyl ether) (PS-b-PMVE) diblock as external branches, are described. The dendrigrafts are observed by AFM and TEM as egglike or long cylindrical objects which can self-organize intramolecularly in segregated subdomains forming flowerlike or strings of flowerlike objects. In organic solvents the dendrigrafts behave as fully soluble isolated macromolecules and show in water a low critical solubility temperature (LCST) at t > 30 degrees C. The ability of the amphiphilic PS-b-PMVE dendrigrafts to complex and transport in water organic (pyrene) and metallo-organic (manganese tetraphenyl porphyrin) molecules is investigated. The possibility to stabilize the high oxidation state of metallo-porphyrin complexes through their encapsulation into the dendrigraft is shown.
    Full-text · Article · Apr 2005 · Journal of the American Chemical Society
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    ABSTRACT: We have studied the morphology of self-assembled micelles made of linear and cyclic poly(styrene-b-isoprene) PS-b-PI block copolymers dispersed in selective solvents of the PI block (n-heptane, n-decane). Up to a copolymer concentration of 5 mg mL(-1), the micelles made from linear block copolymer chains adopt a spherical shape. Those arising from cyclic copolymer chains having exactly the same molar mass and volume fraction self-assemble into (i) planar sun. ower-shaped particles at low concentration (c < 0.1 mg mL(-1)), (ii) giant wormlike micelles at intermediate concentration (0.1 mg mL(-1) < c < 2 mg mL(-1)) and (iii) vesicles at higher concentration (2 mg mL(-1) < c < 5 mg mL(-1)). Those results were obtained using dynamic light scattering and in situ freeze-drying cryo-transmission electron microscopy. In this contribution, we discuss the effects of concentration and temperature on the morphology of the self-assembled particles made from both linear and cyclic PS-PI copolymers, and highlight the surprising vesicle formation in cyclic block copolymer solutions.
    Full-text · Article · Feb 2005 · Faraday Discussions
  • C Lefebvre · R Borsali · M Schappacher · A Deffieux

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