Abstract
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale.
Highlights
For repulsive particles, to condensed islands of larger mobility at moderate attractions[8]
We show how small changes in local structure signal the onset of bond formation
Our results evidence the proposed connection between gels and attractive glasses[10,13], and shed new light on this transition between two disordered solids governed by different microscopic physics
Summary
For repulsive particles, to condensed islands of larger mobility at moderate attractions[8]. It was recently established that there are distinct differences in the glass transition in two and in three dimensions[18]. It remains a challenge to establish the transitions in global and local dynamics occurring during the attractive glass transition in three dimensions. In this paper we use three-dimensional confocal fluorescence imaging to explore the nature of the transition from repulsive to attractive colloidal glasses upon introducing weak bonding interactions. We show how small changes in local structure signal the onset of bond formation. This results in a critical onset for the attractive glass. Our results evidence the proposed connection between gels and attractive glasses[10,13], and shed new light on this transition between two disordered solids governed by different microscopic physics
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