Reconfigurable Slippery Gradient Structure for Programmable
Droplet Self-Propulsion

Ryo Sakai; Shunto Arai; Takashi Hiroi; Ryota Tamate; Timothée Mouterde; Mizuki Tenjimbayashi

doi:10.1021/acs.langmuir.6c02822

Journal article Reconfigurable Slippery Gradient Structure for Programmable Droplet Self-Propulsion

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Ryo Sakai, Shunto Arai, Takashi Hiroi, Ryota Tamate, Timothée Mouterde, Mizuki Tenjimbayashi. Reconfigurable Slippery Gradient Structure for Programmable Droplet Self-Propulsion. Langmuir. 2026, (), . https://doi.org/10.1021/acs.langmuir.6c02822

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Transporting millimetric droplets on a surface is fundamental for droplet fluidics, which requires minimizing droplet sticking and energy input. One promising strategy is tethering the self-propelling ability to droplets on non-sticking surfaces. Self-propulsion is achieved by forming a gradient structure on the substrate. Typically, the gradient is highly directional and non-reprogrammable, making the regulation of transport challenging. Here, we report droplets self-propel from the edge to the center of the substrate. The substrate surface is covered with a stabilized lubricant that exhibits droplet slipperiness. Near the substrate edge, a lubricant thickness gradient forms, which self-propels the droplet. This property enabled the regulated self-propelling of droplets by spatio-temporal edge-shape design. The edge shape determines the direction of the droplet's self-propulsion. Moreover, the in-situ edge appearance/disappearance, achieved by separating/connecting two neighboring coated substrates, enabled the regulation of self-propelling timing because the lubricant gradient structure is reconfigurable. We demonstrate droplets' self-climbing, upside-down self-propelling, in situ stop-and-go motion, two-droplet attractive motion, and reconfigurable two-dimensional droplet motion. We also demonstrate that the sliding droplet on the zig-zag-shaped substrate moves along with the substrate's shape due to the edge self-propelling. These droplet manipulations require no special devices, making them increasingly accessible.

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