In situ characterization of crystallization and melting of soft, thermoresponsive microgels by small-angle X-ray scattering

Dmitry Lapkin, Nastasia Mukharamova, Dameli Assalauova, Svetlana Dubinina, Jens Stellhorn, Fabian Westermeier, Sergey Lazarev, Michael Sprung, Matthias Karg, Ivan A. Vartanyants (Corresponding author), Janne-Mieke Meijer (Corresponding author)

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Abstract

Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, ranging from fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive polymers, the volume fraction can be tuned by temperature, making them excellent systems to experimentally study phase transitions in dense colloidal suspensions. However, investigations of phase transitions at high particle concentration and across the volume phase transition temperature in particular, are challenging due to the deformability and possibility for interpenetration between microgels. Here, we investigate the dense phases of composite core-shell microgels that have a small gold core and a thermoresponsive microgel shell. Employing Ultra Small-Angle X-ray Scattering, we make use of the strong scattering signal from the gold cores with respect to the almost negligible signal from the shells. By changing the temperature we study the freezing and melting transitions of the system in situ. Using Bragg peak analysis and the Williamson-Hall method, we characterize the phase transitions in detail. We show that the system crystallizes into an rhcp structure with different degrees of in-plane and out-of-plane stacking disorder that increase upon particle swelling. We further find that the melting process is distinctly different, where the system separates into two different crystal phases with different melting temperatures and interparticle interactions.


Original languageEnglish
Pages (from-to)1591-1602
Number of pages12
JournalSoft Matter
Volume18
Issue number8
DOIs
Publication statusPublished - 28 Feb 2022

Bibliographical note

Funding Information:
We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III synchrotron facility and we would like to thank all the beamline staff for assistance in using Coherence Application beamline P10. We would like to thank Andrei Petukhov for valuable discussions. We further acknowledge Astrid Rauh for the particle synthesis, Max Schelling for the DLS measurements and Sanam Foroutanparsa for the TEM images. 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. D. L., N. M., D. A., S. L. and I. A. V. acknowledge the Helmholtz Associations Initiative Networking Fund (Grant No. HRSF-0002) and the Russian Science Foundation (Grant No. 18-41-06001). I. A. V. acknowledges the financial support of the Russian Federation represented by the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2021-1352). S. L. acknowledges Competitiveness Enhancement Program Grant of Tomsk Polytechnic University and the Governmental program ‘‘Science’’, project No. FSWW-2020-0014.

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