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 materials 1 . Patchy colloids of different shapes, patterns and functionalities 2 are considered the new building blocks of a bottom-up approach toward the realization of selfassembled bulk materials with predefined properties 3‐7 . The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and microscales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies 8 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 liquids 8 —liquid states with vanishing density—and equilibrium gels 8‐10 —