Optical tweezers as a micro-rheological probe of fluid-fluid surfaces

Using our newly developed technique of OT, we measured the anisotropic hydrodynamic mobility of a colloidal particle by tracking its thermal motion in an optical trap located near fluid-fluid interfaces, namely, liquid-vapor and liquid-liquid interfaces. The method requires no controlled fluid flow, is independent of conservative interactions between particle and interface, and resolves distance dependent friction to within a fraction of the particle radius. Near the liquid-vapor interface, our experiments show for the first time that friction decreases below that in the bulk, corresponding to predictions of a ‘‘perfect-slip’’ surface. (With V.R. Daria (JCSMR, ANU), G.M. Wang, R. Prabhakar (Monash)).


  • G.M. Wang, R. Prabhakar, and E.M. Sevick, “Hydrodynamic mobility of an optically trapped particle near fluid-fluid interfaces”, Phys. Rev. Lett. 103,  248303 (2009).
  • R. Prabhakar, E.M. Sevick, and D.R.M. Williams, “Coarse-graining intramolecular hydrodynamic interactions in dilute solutions of flexible polymers”, Phys. Rev. E. 76, 011809:1-12 (2007).