Nonlinear Motion of Optically Torqued Nanorods

We apply light torques to single optically trapped glass nanorods suspended in water. The resulting motion is carefully studied experimentally and consists of two distinct regimes: a linear regime where the rod angle increases linearly with time and a nonlinear regime where the rod angle changes nonlinearly, experiencing accelerations and rapid reversals. We motivate a theoretical model for the motion of such nanorods, which agrees extremely well with the observed motion. In this report, the trapped and torqued nanorods move without influence from surfaces. Such a model system is helpful to understanding the more complex motion that occurs near a surface. Studying such nonlinear motion both free of, and near, a surface is important for understanding nanofluidics and hydrodynamic motion at the nanoscale. As such, we will also present some data on how the motion is different close to a surface.