Dynamically induced effective interaction in periodically driven granular mixtures

We discuss the microscopic origin of dynamical instabilities and segregation patterns discovered in granular mixtures under oscillating horizontal shear, by investigating, via molecular dynamics simulations, the effective interaction between like-particles. This turns out to be attractive at short distances and strongly anisotropic, with a longer range repulsive shoulder along the direction of oscillation. This features explain the system rich phenomenology, including segregation and stripe pattern formation. Finally, we show that a modified Cahn-Hilliard equation, taking into account the characteristics of the effective interaction, is capable of describing the dynamics of the mixture.