SAXS Investigation of Core-Shell Microgels with High Scattering Contrast Cores: Access to Structure Factor and Volume Fraction

Marco Hildebrandt, Sergey Lazarev, Javier Pérez, Ivan A. Vartanyants, Janne-Mieke Meijer (Corresponding author), Matthias Karg (Corresponding author)

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Abstract

To explore dense packings of soft colloids, scattering experiments are ideal to access the structure factor. However, for soft microgels, determination of the structure factor is difficult because of the low contrast of the polymer network and potential microgel interpenetration and deformation that change the form factor contribution. Here, we employ small-angle X-ray scattering (SAXS) to study soft, thermoresponsive microgels with poly-N-isopropylacrylamide (PNIPAM) shells and gold nanoparticle cores. The scattering of the gold cores dominates the scattering patterns and allows precise determination of the microgel volume fraction over a broad range of concentrations. At high volume fractions, we find distinct patterns with sharp Bragg peaks allowing extraction of the structure factor and characterization of the phases combined with UV-vis spectroscopy. The unique scattering contrast of our core-shell microgels combined with SAXS opens up new ways to investigate dense packings of soft microgels including in situ studies of phase transitions.

Original languageEnglish
Pages (from-to)2959-2969
Number of pages11
JournalMacromolecules
Volume55
Issue number7
DOIs
Publication statusPublished - 12 Apr 2022

Bibliographical note

Funding Information:
The authors acknowledge SOLEIL for provision of synchrotron radiation facilities and thank Javier Perez for assistance in using beamline SWING (Proposal number 20181613). The authors thank the Center for Structural Studies (CSS) that is funded by the Deutsche Forschungsgemeinschaft (DFG Grant numbers 417919780 and INST 208/761-1 FUGG) for access to the SAXS instrument. The authors acknowledge the DFG and the state of NRW for funding the cryo-TEM (INST 208/749-1 FUGG) and Marius Otten from Heinrich-Heine-University Düsseldorf for his assistance with the TEM measurements.

Funding Information:
J.M.M. acknowledges financial support from the Netherlands Organization for Scientific Research (NWO) (016.Veni.192.119). M.K. acknowledges the German Research Foundation (DFG) for funding under grant KA3880/6-1.

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