Hydrodynamics of micro-objects near curved surfaces (Presentation Recording)

Boundary walls have a strong influence on the drag force on optically trapped object near surface. Faxen’s correction has shown how a flat surface modifies the hydrodynamic drag. However, to date, the effect of curved walls at microscopic scale on both translational and rotational movement of micro-objects has not been studied. Here we describe our experiments which aim to study the drag force on optically trapped particles moving near walls with different curvatures. The curved walls were made using 3D laser nano-printing (Nanoscribe), and optical tweezers were used to trap micro-objects near the walls. The translational and rotational motion of the optically trapped particle is related to the drag coefficients. By monitoring the change in the motion of particle, we determined the increase in drag force for particles translating or rotating at different distances from surfaces with different curvatures. These results are essential for calibrating the drag force on particles, and thus enable accurate rheology at the micron-scale. This opens the potential for microrheology under different conditions, such as within microdevices, biological cells and studies of biological processes.