Structures And Dynamics Of Attractive Colloidal Glasses

Colloidal systems have been widely used in condensed matter physics. The hardsphere colloidal is the most simple and representative colloidal system and the interparticleinteraction is pure repulsive. However, the simple system possess very rich physicalphenomena. As increasing the packing fraction, the system undergoes a phase transitionfrom the fluid phase to crystal or glassy state. The hard sphere colloidal glass transition hasbeen investigated extensively by the experiment, theory and simulation. Researchers findthat adding a small, short-range attraction to the repulsive hard sphere glass cansurprisingly melt it into an attractive liquid. Increasing the attraction further, the systemcomes back to another glass, i.e. an attractive glass. In this thesis, we developed moleculardynamics simulation method and explored the structures and dynamics of differentattractive colloidal glasses, with the aim of better understanding how the interparticlepotentials affect the properties of glasses. Specifically, we adopt the binary Lennard-Jonesglass as our model system and truncates the interaction potential beyond a cutoff at typicalinterparticle distance to tune the range of potential. We find that attractive ranges affect thedynamics and dynamical heterogeneity quantitatively and qualitatively, while they havelittle effect on the glassy structure. For the repulsion-driven (WCA) glass, the particledynamics are fast. As increasing the attractive range, the appearance of short-rangeattraction leads to the formation of long-lived bonds between particles, and because thesebonds are difficult to break, particles move slowly and need more time to escape the cage,the relaxation time become large and rearrangements occur less often. When arearrangement does occur, attractive bonds pull neighboring particles, causing them toparticipate in the rearrangement. As a result, more particles are involved in cooperativerearrangement regions in attractive glasses. Compared to repulsive WCA glasses, the attractive LJ glass dynamics are found to be heterogeneous over a wider range of time andlength scales, the attractive interaction can increase the dynamical heterogeneities of glassysystem.