Observation of liquid glass in suspensions of ellipsoidal colloids

Significance Using tailor-made colloids and confocal microscopy, we study the effect of shape on the glass transition in 3D suspensions of ellipsoidal colloids. Experimental data, supporting simulations, and a theoretical analysis reveal a unique state: liquid glass. In liquid glasses, orientational degrees of freedom are frozen whereas translation is free. Global nematic order is absent. We show that, in the liquid glass state, nematic precursors as hitherto unknown structures exist. In these, nematic order is suppressed by the intersection of clusters of ordered particles with differently ordered particles. Our data thus give insight into the glass transition and reveal an additional state of matter. The latter is expected to also have implications in liquid crystal formation.
Despite the omnipresence of colloidal suspensions, little is known about the influence of colloid shape on phase transformations, especially in nonequilibrium. To date, real-space imaging results at high concentrations have been limited to systems composed of spherical colloids. In most natural and technical systems, however, particles are nonspherical, and their structural dynamics are determined by translational and rotational degrees of freedom. Using confocal microscopy of fluorescently labeled core–shell particles, we reveal that suspensions of ellipsoidal colloids form an unexpected state of matter, a liquid glass in which rotations are frozen while translations remain fluid. Image analysis unveils hitherto unknown nematic precursors as characteristic structural elements of this state. The mutual obstruction of these ramified clusters prevents liquid crystalline order. Our results give insight into the interplay between local structures and phase transformations. This helps to guide applications such as self-assembly of colloidal superstructures and also gives evidence of the importance of shape on the glass transition in general.