Published December 10, 2024 | Published
Journal Article Open

Active doping controls the mode of failure in dense colloidal gels

  • 1. ROR icon California Institute of Technology

Abstract

Mechanical properties of disordered materials are governed by their underlying free energy landscape. In contrast to external fields, embedding a small fraction of active particles within a disordered material generates nonequilibrium internal fields, which can help to circumvent kinetic barriers and modulate the free energy landscape. In this work, we investigate through computer simulations how the activity of active particles alters the mechanical response of deeply annealed polydisperse colloidal gels. We show that the "swim force" generated by the embedded active particles is responsible for determining the mode of mechanical failure, i.e., brittle vs. ductile. We find, and theoretically justify, that at a critical swim force the mechanical properties of the gel decrease abruptly, signaling a change in the mode of mechanical failure. The weakening of the elastic modulus above the critical swim force results from the change in gel porosity and distribution of attractive forces among gel particles, while below the critical swim force, the ductility enhancement is caused by an increase of gel structural disorder. Above the critical swim force, the gel develops a pronounced heterogeneous structure characterized by multiple pore spaces, and the mechanical response is controlled by dynamical heterogeneities. We contrast these results with those of a simulated monodisperse gel that exhibits a nonmonotonic trend of ductility modulation with increasing swim force, revealing a complex interplay between the gel energy landscape and embedded activity.

Copyright and License

© 2024 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

Acknowledgement

We acknowledge financial support from the Department of Energy under Grant DE-SC0022966. The simulations in this work are performed on the CFN computing facility at the Brookhaven National Laboratory (proposal ID: GUP-310204). T.Z. thanks S. Chen, H. Row, S. Mallory, D. Frag, X. Wan, and X. Cheng for their helpful discussions.

Funding

We acknowledge financial support from the Department of Energy under Grant DE-SC0022966.

Contributions

T.Z. and J.B. designed research; T.Z. performed research; T.Z. and J.B. contributed new reagents/analytic tools; T.Z. and J.B. analyzed data; and T.Z. and J.B. wrote the paper.

Data Availability

All study data are included in the article and/or SI Appendix.

Supplemental Material

Supporting information (PDF).

Files

zhou-brady-2024-active-doping-controls-the-mode-of-failure-in-dense-colloidal-gels.pdf
Files (32.4 MB)

Additional details

Created:
December 10, 2024
Modified:
December 10, 2024