Daniel Bonn, University of Amsterdam and Ecole Normale Superieure, Amsterdam, Netherlands
The study of colloids allowed for a significant contribution to elucidating the basic physics of glass transition. In colloidal systems, as the particle volume fraction is increased, the particles become increasingly slower and for even higher volume fractions the glass transition is encountered. On the other hand, colloidal gels are known to form at extremely low volume fractions in the presence of strong attractions. Gelation and the glass transition have important similarities. Both are ergodic to non-ergodic transitions that are kinetic, rather than thermodynamic in origin, and distinguishing between these two types of non-ergodic states experimentally is a longstanding controversy We report experiments that allow for distinguishing gels from glasses in the Laponite system. This allows us to show that for a range of concentrations, two distinctly different non-ergodic states can result at late times: either the glass or the gel forms at late times with roughly equal probability. There is no way to tell beforehand which of the two options will be taken by the sample, suggesting that there are at least two metastable minima in the system. We also report that a third state: an attractive glass may be found in the same system.