Directional flow characteristics of droplets on superhydrophobic-superhydrophilic patterned microchannel surfaces

Directional flow of droplets is important for the microfluidic and microchannel heat sink devices. However, the current fabrication methods of metal microchannels that can achieve self-driven directional flow of droplets are costly, inefficient, and cannot be mass-produced. To overcome these shortcomings, superhydrophobicsuperhydrophilic (SS) patterned microchannel surfaces with self-driven directional flow performance were prepared on large-area aluminum alloy substrates by chemical and laser etching. Multiple parallel super- hydrophobic microchannels with a contact angle of 133 degrees were prepared by chemical etching and FAS modification. Superhydrophilic pattern "F" with a contact angle of 0 degrees was processed in the microchannels by laser etching. With the design and preparation strategy, the self-driven directional flow of droplets in aluminum SS microchannels is achieved. The flow characteristics of droplets were adjusted by varying the horizontal distance (h) and angle (alpha) of the pattern "F". It was found that the maximum flow velocity of droplet self-driven flow on the SS microchannel surface was 3.28 mm/s with alpha=0 degrees and h = 0.3 mm. The spontaneous movement of the droplets on the SS microchannels is attributed to the imbalance between the diffusion force of the pattern "F" and the pinning force of the superhydrophobic microchannels. The novel SS microchannels constructed with self- driven directional flow in aluminum alloys show great application potential in the field of microfluidics and microchannel heat dissipation.