Structure of PEP-PEO block copolymer micelles: Exploiting the complementarity of small-angle X-ray scattering and static light scattering

Grethe Vestergaard Jensen, Qing Shi, María J. Hernansanz, Cristiano L. P. Oliveira, G. Roshan Deen, Kristoffer Almdal, Jan Skov Pedersen

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    Abstract

    The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP-PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8-49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core-shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.
    Original languageEnglish
    JournalJournal of Applied Crystallography
    Volume44
    Issue number3
    Pages (from-to)473-482
    ISSN0021-8898
    DOIs
    Publication statusPublished - 2011

    Keywords

    • Copolymerization
    • Core-shell model
    • static light scattering
    • Ethylene oxides
    • Internal structure
    • Light scattering
    • block copolymers
    • Spherical micelles
    • Refraction
    • Polyethylene oxides
    • small-angle X-ray scattering
    • Scattering vectors
    • Small-angle neutron scattering
    • Micelle structure
    • contrast variation
    • Ethanol
    • micelles
    • Propylene
    • Block copolymers
    • Two-component.
    • Length scale
    • Contrast variation
    • Block copolymer micelles
    • X ray scattering
    • Micelle morphology
    • Micelles
    • Neutron scattering
    • Morphology
    • X rays
    • Ethanol solutions
    • Ethylene
    • PEO molecular weight

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