Hard Spheres: Is There a Glass Transition Below Random Close Packing?

Abstract:  The microscopic relaxation time, tau, of hard sphere systems grows dramatically as their volume fraction increases above phi ~0.55. This behavior is similar to that of molecular glass  formers approaching the glass transition temperature: hard spheres are  indeed regarded as the simplest system exhibiting a glass transition and are often studied as a model system against which various compteing theories may be tested. The very nature of the divergence of tau remains however controversial. We present new light scattering measurement and numerical simulations that extend previous data  by two orders of magnitude in relaxation time. Our data rule out  the existence of an ideal Mode Coupling divergence at phi ~0.58, as previously proposed. They rather show that tau diverges according to a gerneralized VFT law, tau~exp[B/(phi_0-phi)^a], with a ~ 2 and phi_0 close to, but smaller than, the random close packing volume fraction.