Asymmetric surfaces can achieve spontaneous droplet transport through Laplace pressure gradients. A mechanistic understanding of droplet dynamics on such surfaces is critical for their applications. However, it poses a challenge to conduct experiments to capture the details of droplet self-transportation on asymmetric surfaces, and there are a few existing studies at the macroscopic scale. In this work, a numerical model of superwettable wedge-shaped surfaces (SWS) was established for systematically investigating the self-transportation of millimeter-scale droplets on the SWS. We systematically investigated the self-transportation behavior on the SWS after the model was verified against our experimental characteristics and data. Studies demonstrated that the released surface energy ΔGs of droplets is the main source of kinetic energy (ΔGs is approximately 20 times greater than the gravitational potential energy) that enables self-transport and transport efficiency. It could be improved by increasing droplet volume (from 25 to 65 μl), wedge angle (from 1° to 2.5°), the hydrophilicity of the wedge-shaped area, and the hydrophobicity of the non-wedge-shaped area. The average transmission speed of a 45 μl droplet can reach 241 mm/s (wedge angle 2.5°). Moreover, it was found that excessive volume or insufficient hydrophilicity in the wedge-shaped area leads to a reduction in transport efficiency. Furthermore, the droplet transport on the SWS in an oily environment was investigated. This study contributes to the optimal droplet manipulation on the SWS and is also expected to enhance the understanding of the self-transportation behavior of droplets in multi-fluid environments.
Sun et al. (Mon,) studied this question.
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