Structure and sticky spheres near and far from equilibrium

Paddy Royall
University of Bristol, School of Chemistry
Friday, June 15, 2012
119 Physics | 2:50pm

A liquid falling out of equilibrium, and undergoing dynamical arrest is among the key outstanding problems in condensed matter physics. Whether structure is a cause of dynamical arrest remains a topic of strong debate, however it has emerged recently that, upon the approach to the glass transition, many materials show clear structural signatures. In the system in question, of hard and sticky spheres, successively larger clusters are preferred which minimize the free volume at the expense of entropy. Here we go further : pushing a system of hard or sticky spheres out of equilibrium we find a clear structural signature : highly non-equilibrium states are comprised of tetrahedra, the simplest structural unit in 3D space : this is a direct consequence of even local rearrangement being suppressed out of equilibrium. Our analysis also identifies glasses as systems which gradually fall out of equilibrium, while gels, in their relation metastable liquid-gas phase separation, are formed immediately upon crossing the spinodal line : thus vitrification is continuous and gelation is discontinuous and intrinsically far from equilibrium.