Arrested demixing opens route to bigels.

Understanding and, ultimately, controlling the properties of amor-phous materials is one of the key goals of material science. Among the different amorphous structures, a very important role is played by colloidal gels. It has been only recently understood that colloidal gels are the result of the interplay between phase separation and arrest. When short-ranged attractive colloids are quenched into the phase-separating region, density fluctuations are arrested and this results in ramified amorphous space-spanning structures that are capable of sustaining mechanical stress. We present a mecha-nism of aggregation through arrested demixing in binary colloidal mixtures, which leads to the formation of a yet unexplored class of materials--bigels. This material is obtained by tuning interspecies interactions. Using a computer model, we investigate the phase behavior and the structural properties of these bigels. We show the topological similarities and the geometrical differences be-tween these binary, interpenetrating, arrested structures and their well-known monodisperse counterparts, colloidal gels. Our find-ings are supported by confocal microscopy experiments performed on mixtures of DNA-coated colloids. The mechanism of bigel for-mation is a generalization of arrested phase separation and is therefore universal. [ABSTRACT FROM AUTHOR]