Shear-Induced Structural and Functional Transformations of Poly(N-vinylcaprolactam) Microgels

Emilia Izak-Nau, Dan E. Demco, Susanne Braun, Christoph Baumann, Andrij Pich, Robert Goestl*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

16 Citations (Web of Science)


We here performed an in-depth investigation of the behavior of microgels (mu gels) and their associated physicochemical transformations under shear force. Thermo- and mechanoresponsive poly(N-vinylcaprolactam) (PVCL) mu gels (d similar to 400 nm) cross-linked with a force-responsive mechanofluorophore in different crosslinking degrees were synthesized and examined. Fluorescence spectroscopy (FS), confocal laser scanning microscopy (CLSM), dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryoTEM), high-resolution magic-angle sample spinning (HRMAS) nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) are used to characterize the mu gels before, during, and after shearing with different shear rates and intensities. The obtained results suggest nonuniform structural features consisting of a softer outer "corona" and a harder particle "core" (cross-linker-rich). Upon shearing, the mu gels rapidly lose their corona and the cores agglomerate altering mu gel functionality. Surprisingly, mu gels degrade promptly, even when subjected to low shear forces, such as the extrusion through a needle. This has potential implications for all applications in which shear forces in solution are expected, including extrusion, injection, and filtration processes involving colloidal mu gel solutions as well as circulation within the bloodstream of living organisms.

Original languageEnglish
Pages (from-to)1682-1691
Number of pages10
JournalACS Applied Polymer Materials
Issue number4
Publication statusPublished - Apr 2020


  • microgels
  • mechanical properties
  • shear force
  • mechanochemistry
  • colloids

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