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Observation of empty liquids and equilibrium gels in a colloidal clay


The relevance of anisotropic interactions in colloidal systems has recently emerged in the context of the rational design of new soft materials1. Patchy colloids of different shapes, patterns and functionalities2 are considered the new building blocks of a bottom-up approach toward the realization of self-assembled bulk materials with predefined properties3,4,5,6,7. The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and micro-scales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies8 suggest that the phase diagram of patchy colloids can be significantly altered by limiting the particle coordination number (that is, valence). New concepts such as empty liquids8—liquid states with vanishing density—and equilibrium gels8,9,10—arrested networks of bonded particles, which do not require an underlying phase separation to form11—have been formulated. Yet no experimental evidence of these predictions has been provided. Here we report the first observation of empty liquids and equilibrium gels in a complex colloidal clay, and support the experimental findings with numerical simulations.

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Figure 1: Experimental behaviour of diluted Laponite suspensions.
Figure 2: Behaviour of the patchy-particle model for Laponite discs.
Figure 3: Phase diagram of diluted Laponite suspensions, in the waiting-time-versus-concentration plane, resulting from the combined experimental and numerical results.

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B.R., L.Z. and R.A. thank G. Ruocco for his encouragement and advice during the course of this project. We thank C. De Michele for the code generating the snapshots of Fig. 2 and the European Synchrotron Radiation Facility for beamtime. E.Z. and F.S. acknowledge financial support from ERC-226207-PATCHYCOLLOIDS and ITN-234810-COMPLOIDS.

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B.R., L.Z. and R.A. carried out experiments. E.Z. and F.S. did the modelling and numerical simulations. M.S., A.M. and T.N. gave technical support and conceptual advice for the SAXS experiment. All authors discussed the results and implications and contributed to the writing of the manuscript.

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Correspondence to Barbara Ruzicka or Emanuela Zaccarelli.

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The authors declare no competing financial interests.

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Ruzicka, B., Zaccarelli, E., Zulian, L. et al. Observation of empty liquids and equilibrium gels in a colloidal clay. Nature Mater 10, 56–60 (2011).

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