Molecular-Level Mechanical Instabilities and Enhanced Self-Diffusion in Flowing Liquids

Molecular simulations show that shear strains arising from liquid flow cause local minima of the potential-energy surface to disappear, leading to mechanical instabilities which force the system towards alternate local minima. Associated with these mechanical instabilities are irreversible atomic displacements, which are strain activated rather than thermally activated. These displacements generate self-diffusion in excess of that from thermal-activation alone and give rise to the shear-enhanced self-diffusion known to occur in flowing liquids and concentrated suspensions of particles. The magnitude of this enhancement is shown to decrease with increasing temperature and strain rate.