Laminar Drag Reduction in Microchannels with Quasi-liquid Slippery Polymer Brush Surfaces

In laminar flows in microchannel, drag reduction is capable of reducing the required pumping power in microchannel, enhancing microfluidic cooling, augmenting electrokinetic energy harvesting, and enabling better flow control in chemical and biological devices. One important passive drag reduction method is to modify the wetting property of the microchannel surfaces, such as textured superhydrophobic and slippery liquid-filled surfaces. However, there are two significant challenges associated with textured slippery surfaces: 1) the surface coverage of fluid lubricant layer is often limited, restricting overall drag reduction; and 2) fluid lubricant suffers from poor durability. In recent studies, a novel type of non-textured slippery quasi-liquid polymer brush surfaces have been developed. This novel non-textured liquid-like slippery surface represents a promising candidate for drag reduction. In this work, we fabricated microchannels with slippery polymer brush grafted surfaces and microchannels made by silicon surfaces. To investigate the drag reduction induced by the slippery polymer brush surfaces, we measured the pressure drops along the microchannels under various flow rates and Reynolds numbers. The drag reduction coefficient and corresponding fluid slip length are calculated. The drag reduction coefficient between 10% to 15% and fluid slip length in micron scale are achieved.