Hong Kong researchers have discovered a novel approach to regulate the dispersion dynamics of liquids on surfaces. Traditionally, it was believed that the direction of liquid spread was determined solely by the surface design and could not be customized. However, this new research challenges that notion by showing that liquids with different surface tensions can be made to select their directions of propagation on the same surface.
The key to achieving this customization lies in the use of 3D macro ratchets with double-entry cambers. These sophisticated structures can be manufactured using 3D printing, but the layer-by-layer printing process introduces surface defects similar to microgrooves. Previous approaches required additional polishing treatments to remove these defects, increasing complexity and limiting practical applications.
In this study, the researchers took a different approach. Instead of removing surface defects, they took advantage of them to regulate the expansion phase map of liquids. By designing streamlined, dual-scale ratchets with micro-slots, they were able to achieve fluid directional steering similar to that found in natural phenomena.
Further experiments revealed that the orientation of the microgrooves plays a crucial role in regulating liquids with moderate wettability.
“It provides a new surface design that is easy to fabricate or replicate, without sacrificing the directional function of liquids,” said Zuankai Wang, a researcher at the Department of Mechanical Engineering at Hong Kong Polytechnic University.
“The microgrooves arranged perpendicular to the ratchet tilt direction serve as a retard valve to slow down the dispersion of liquids on the lateral surface of the pawls, while the microgrooves parallel to the ratchet tilt direction would promote the liquid dispersion due to capillarity, therefore, the latter is more beneficial for backward dispersion of liquids”.
The findings of this study challenge conventional thinking and open up new possibilities for the design and fabrication of surfaces that can precisely control the dispersion of liquids. The researchers are now delving into the mechanisms of liquid-solid interactions and exploring additional functionalities that can be achieved by incorporating different ingredients into the materials.
This research demonstrates how seemingly undesirable surface defects can be harnessed to create functional surfaces, turning waste into treasure. By embracing and understanding the intricacies of microscale structures, engineers can unlock new applications in various fields, including oil-water separation, water harvesting, heat management, microfluidics, advanced manufacturing, and biomimetics.
“What we know is just the tip of the iceberg, more advanced visualization tools can be employed to reveal how liquid and solid structures interact on the microscale, or we can even introduce other features by adding different ingredients to materials,” Wang said.
The possibilities are vast, and future research will undoubtedly reveal more about the potential of these innovative approaches to liquid handling.
The full research paper, titled “Selective Liquid Directional Steering Enabled by Dual-Scale Reentrant Pawls” can be found in the International Journal of Extreme Manufacturing, at this link.
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