Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 411129
Title Looped structure of flowerlike micelles revealed by (1)H NMR relaxometry and light scattering
Author(s) Graaf, A.J. de; Boere, K.W.M.; Kemmink, J.; Fokkink, R.G.; Nostrum, C.F. van; Rijkers, D.T.S.; Gucht, J. van der; Wienk, H.; Baldus, M.; Mastrobattista, E.; Vermonden, T.; Hennink, W.E.
Source Langmuir 27 (2011)16. - ISSN 0743-7463 - p. 9843 - 9848.
Department(s) Physical Chemistry and Colloid Science
Organic Chemistry
Publication type Refereed Article in a scientific journal
Publication year 2011
Keyword(s) block-copolymer micelles - triblock copolymer - aqueous-solution - poly(ethylene glycol) - drug-delivery - aggregation behavior - nmr relaxation - oxide) - micellization - nanoparticles
Abstract We present experimental proof that so-called “flowerlike micelles” exist and that they have some distinctly different properties compared to their “starlike” counterparts. Amphiphilic AB diblock and BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm16kDa-PEG4kDa-pNIPAm16kDa which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG2kDa-pNIPAm16kDa. Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. 1H NMR relaxation measurements showed biphasic T2 relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.
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