Molecular dynamics study of the stability of the hard sphere glass - art. no. 021506

Glassy states have been observed in hard-spherelike colloidal suspensions h owever, some recent work suggests that a stable, one-component hard-sphere glass doesn't exist. A possible resolution of this dilemma is that colloida l glass formation results from a small degree of particle polydispersity. I n order to investigate this further, we used the molecular-dynamics method to explore the phase behavior of both one- and two-component hard-sphere sy stems. It was found that the metastable fluid branch of the one-component s ystem ceased to exist at a volume fraction marginally above melting, instea d this system always crystallized within a relatively short period of time. Binary systems with a size ratio gamma =0.9 were then used as the simplest approximation to model a polydisperse hard-sphere colloidal system. Here t he crystallization process was slowed down dramatically for all volume frac tions and the fluid state was maintained for many relaxation times. Indeed, at the lowest volume fraction phi = 0.55 no sign of crystallization was se en on the simulation time scale. The systems at intermediate volume fractio ns did eventually crystallize but at the highest volume fraction of phi = 0 .58, a dramatic slowing down in the crystallization process was observed. T his is qualitatively in agreement with the experimental results on colloida l suspensions. Using the insight gained from this paper, the reasons behind a polydisperse system forming a stable glass, in contrast to the one-compo nent system, are elucidated.