Tilting and Tumbling of Janus Nanoparticles at Sheared Interfaces.

We investigate the response of a single Janus nanoparticle adsorbed at an oil-water interface to imposed shear flows using molecular dynamics simulations. We consider particles of different geometry, including spheres, cylinders, and discs, and tune their degree of amphiphilicity by controlling the affinity of their two sides to the fluid phases. We observe that depending on the shape, amphiphilicity, and the applied shear rate, two modes of rotational dynamics takes place: a smooth tilt or a tumbling motion. We demonstrate that irrespective of this dynamic behavior, a steady-state orientation is eventually achieved as a result of the balance between the shear- and capillary-induced torques, which can be tuned by controlling the surface property and flow parameters. Our findings provide insight on using flow fields to tune particle orientation at an interface and to utilize it to direct their assembly into ordered monolayers.