Are particle gels “glasses”?

Abstract

We propose an analogy between a new type of glass, recently found within the mode coupling theory framework, and a particle gel, experimentally observed in colloidal suspensions where the particles have attractive interactions. We report the study of a colloidal system model, made of particles with hard core interacting via an attractive square-well potential. The well-width has a range much shorter than the particle diameter. We find new phenomena in the temperature-composition plane related to the width of the attractive interactions, namely a re-entrant behaviour in the ‘phase’ diagram and a coexistence line between two types of glasses. One has been identified as the commonly studied colloidal glass and the other as a new type, the ‘attractive’ glass, that can be viewed as a particle gel. The coexistence line terminates at an end-point, named A 3, after which the gel and the colloidal glass become indistinguishable. We also show characteristic features of the normalised density correlators, for the gel at a relatively low density and close to this singularity point, where the gel and the colloidal glass start to coexist. For the latter it is remarkable to note that the density correlators show a logarithmic time decay.