Micron-Size "Giant" Hydrodynamic Slip at an Oil/Polydimethylsiloxane Surface from Measurements of the Dielectrophoretic Motion of Water Droplets Along the Surface

We present a measurement of large hydrodynamic slip at the interface between a mineral oil and polydimethylsiloxane (PDMS). Pairs of surfactant-stabilized water droplets are formed in oil via microfluidic flow focusing, and merge due to dielectrophoresis in a uniform electric field  applied parallel to the bottom wall of a microchannel.  Order one micron slip lengths  are obtained by modeling the dielectrophoretic motion of the droplets in close proximity to the channel wall. The large slip at the PDMS surface suggests that the air retained in PDMS because of its nanoporous hydrophobicity  leads to a low friction layer of nanobubbles at the interface, and this  represents a general means for generating large slip without (superhydrophobic) surface texturing.