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Edited by Noel A. Clark, University of Colorado, Boulder, CO, and approved January 2, 2020 (received for review May 30, 2019)
Significance
Networks of mesoscopic colloidal particles, gels, are everyday materials. Yet, our understanding of colloidal gels lags far behind their utility: Gels are out of equilibrium, so their properties change over time, often with significant consequences, such as failure of the material. However, until now, we were confident of one thing: To aggregate into a network, the colloidal particles need to attract one another. Here, we show that, in fact, colloids can form a network without significant attractions. This is surprising because particles without an attraction usually distribute themselves throughout space, rather than forming a network of particle-rich and -poor regions. Our work opens the way to “nonsticky gels” and a deeper understanding of this perplexing state of matter.
Abstract
Spinodal demixing into two phases having very different viscosities leads to viscoelastic networks—i.e., gels—usually as a result of attractive particle interactions. Here, however, we demonstrate demixing in a colloidal system of polydisperse, rod-like clay particles that is driven by particle repulsions instead. One of the phases is a nematic liquid crystal with a highly anisotropic viscosity, allowing flow along the director, but suppressing it in other directions. This phase coexists with a dilute isotropic phase. Real-space analysis and molecular-dynamics simulations both reveal a long-lived network structure that is locally anisotropic, yet macroscopically isotropic. We show that our system exhibits the characteristics of colloidal gelation, leading to nonsticky gels.
Footnotes
- ↵1To whom correspondence should be addressed. Email: paddy.royall{at}bristol.ac.uk.
Author contributions: C.F.-C., C.P.R., and J.S.v.D. designed research; C.F.-C. performed research; C.F.-C., C.P.R., and J.S.v.D. analyzed data; and C.F.-C., C.P.R., and J.S.v.D. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
Data deposition: Data are available at the University of Bristol data repository, https://data.bris.ac.uk/data/ (https://doi.org/10.5523/bris.1gfhyy3l2qipg2t8wg6t6f1c0k).
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1909357117/-/DCSupplemental.
Published under the PNAS license.
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Anisotropic viscoelastic phase separation in polydisperse hard rods leads to nonsticky gelation
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