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Structure of PEP–PEO block copolymer micelles: exploiting the complementarity of small‐angle X‐ray scattering and static light scattering
Author(s) -
Jensen Grethe Vestergaard,
Shi Qing,
Hernansanz María J.,
Oliveira Cristiano L. P.,
Deen G. Roshan,
Almdal Kristoffer,
Pedersen Jan Skov
Publication year - 2011
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889811013343
Subject(s) - small angle x ray scattering , micelle , scattering , materials science , copolymer , small angle neutron scattering , neutron scattering , polymer , ethylene oxide , chemical physics , grazing incidence small angle scattering , static light scattering , crystallography , polymer chemistry , chemical engineering , light scattering , chemistry , optics , physics , aqueous solution , composite material , engineering
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.