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Sci Rep. 2019 Sep 25;9(1):13812. doi: 10.1038/s41598-019-50164-6.

Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour.

Author information

1
Department of Physical and Biophysical Chemistry, Bielefeld University, Universitätsstr. 25, 33615, Bielefeld, Germany.
2
Laboratoire Charles Coulomb (L2C), University of Montpellier, CNRS, 34095, Montpellier, France.
3
Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum MLZ, 85748, Garching, Germany.
4
Laboratoire Léon Brillouin, UMR 12 CEA/CNRS, CEA Saclay, 91191, Gif Sur Yvette, France.
5
Department of Physical and Biophysical Chemistry, Bielefeld University, Universitätsstr. 25, 33615, Bielefeld, Germany. thomas.hellweg@uni-bielefeld.de.
6
Lund Institute of Advanced Neutron and X-ray Science (LINXS), IDEON Building: Delta 5, Scheelevägen 19, 22370, Lund, Sweden. thomas.hellweg@uni-bielefeld.de.
7
Laboratoire Charles Coulomb (L2C), University of Montpellier, CNRS, 34095, Montpellier, France. julian.oberdisse@umontpellier.fr.

Abstract

The peculiar linear temperature-dependent swelling of core-shell microgels has been conjectured to be linked to the core-shell architecture combining materials of different transition temperatures. Here the structure of pNIPMAM-core and pNNPAM-shell microgels in water is studied as a function of temperature using small-angle neutron scattering with selective deuteration. Photon correlation spectroscopy is used to scrutinize the swelling behaviour of the colloidal particles and reveals linear swelling. Moreover, these experiments are also employed to check the influence of deuteration on swelling. Using a form-free multi-shell reverse Monte Carlo approach, the small-angle scattering data are converted into radial monomer density profiles. The comparison of 'core-only' particles consisting of identical cores to fully hydrogenated core-shell microgels, and finally to H-core/D-shell architectures unambiguously shows that core and shell monomers display gradient profiles with strong interpenetration, leading to cores embedded in shells which are bigger than their isolated 'core-only' precursor particles. This surprising result is further generalized to different core cross-linker contents, for temperature ranges encompassing both transitions. Our analysis demonstrates that the internal structure of pNIPMAM-core and pNNPAM-shell microgels is heterogeneous and strongly interpenetrated, presumably allowing only progressive core swelling at temperatures intermediate to both transition temperatures, thus promoting linear swelling behaviour.

PMID:
31554839
DOI:
10.1038/s41598-019-50164-6
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