Dynamics of repulsive and attractive glasses 

The glass transition of repulsive hard spheres has been studied extensively, but the effect of (slight) attractive forces between particles remains relatively unexplored. When the volume fraction is increased in a purely repulsive system this reduction of free volume leads to cage formation that restricts particle mobility due to the presence of neighboring particles.

This picture changes dramatically upon the addition of slight attractive forces between particles. At low attraction strengths in the order of 1 kbT weak clustering between the particles leads to an increase in free volume and subsequent melting of the glass. At higher attraction strengths physical bonds start to form between particles that cause another glass transition from the re-entrant liquid into a bond-dominated glass, which is quite different compared to a repulsive glass.

At rest we already observe stark differences between the repulsive and attractive glass, but our main interest lies in understanding the effects of flow upon such systems. By flowing these glassy suspensions through narrow microchannels we impose strong shear forces and create additional hydrodynamic interactions that can lead to structure formation as well. We’re interested in understanding the different effects that geometry, flow and attraction strengths have on the behavior of these glassy suspensions.

We use high-speed confocal microscopy to study these systems; this allows us to follow our particles in time and space, so that we can study the dynamics and structure formation in great detail. We also use different microfluidic techniques to study these systems under flow.