Vertically vibrated systems of granular materials have been used to gain insight on granular segregation for
decades. However, the majority of studies have focused on the rise of a single large
“
intruder
”
particle in an
otherwise monodisperse bed, or binary mixtures. As most industrially relevant granular materials are
characterized by some degree of polydispersity, a study of granular mixtures with additional particle sizes is
warranted to determine the role of polydispersity in granular mixing and segregation. In this work, the
segregation of binary, ternary and polydisperse mixtures of nuts and spheres in a vertically vibrated cylinder
is studied experimentally and computationally. We
fi
nd that the presence of the
other
species
–
besides the
smallest and largest size
–
is responsible for dramatic reductions in the
fi
nal degree of segregation compared
to a binary mixture. In addition, we quantify orders of magnitude reduction in the segregation rate of a
mixture of polydisperse spheres compared to a binary mixture. This reduction in segregation coincides with
an increase in diffusive and convective mixing and correlates with a lower average system density. Voidage
distributions demonstrate the bed packing structure plays an important role in enabling multi-sized systems
to remain in a more mixed state as compared to binary systems. Our observations show that this prototypical
segregation experiment provides as much insight into why materials do not segregate as why they do.