Molecular Dynamics Simulations of Diffusiophoretic Motion of Nanoparticles

Diffusiophoresis refers to the spontaneous motion of particles or polymers in a fluid induced by a concentration gradient of solutes. Large scale molecular dynamics simulations are used to study the diffusiophoretic movement of colloidal particles dispersed in a suspension of nanoparticle solutes that possess a steady-state concentration gradient. This gradient is caused and maintained by a membrane that is transparent to the solvent but allows unidirectional passage of the nanoparticle solutes from one side to the other. By suppressing the overall flow across the system, a concentration gradient of the nanoparticle solutes is established, which leads to a chemical potential gradient for the colloidal particles and drives their diffusiophoretic motion. With this setup, the sign of the diffusiophoretic mobility and its dependence on the size contrast between the diffusiophoretic colloidal particles and the nanoparticle solutes are systematically studied. By elucidating the physics of diffusiophoresis, the results will help reveal the fundamental mechanism underlying the recently observed stratification phenomena in suspensions of colloidal particles with polydisperse size distributions.