Design of Nanofibrous and Microfibrous Channels for Fast Capillary Flow

The speed of capillary flow is a key bottleneck in improving the performance of nanofluidic and microfluidic devices for various applications including microfluidic diagnostics, thermal management heat pipes, micromolding devices, functional fabrics, and oil-water separators. Here, we present a novel nanofibrous or microfibrous hollow-wedged channel (named as W-Channel), which can significantly speed up the capillary flow. The capillary flow in the initial 100 s in the nanofibrous W-Channel was shown to be 8 times faster than that in the single-layer strip of the same material when placed vertically and over 20 times faster when placed horizontally. The enhanced flow under gravity is attributed to the adaptive interplay of capillary pressure and flow resistance within the triangular hollow wedge between the fibrous layers. The W-Channel can be fabricated following a simple procedure using inexpensive materials such as electrospun nanofibers or microfibrous filter papers.