Experimental investigations of self-propelled water surface mini-robots based on droplets motion on superhydrophilic cone channels

Abstract

Self-propelled micro-robots with external devices and chemical reactions have broad applications in energy conservation, biomedical engineering, and targeted drug delivery. However, the utilization of the self-propelled micro-robots is challenging due to the expensive external devices, low durability, and toxic substance emission. In the present study, a green self-propelled water surface mini-robot (SWSM) was reported based on droplet-driven. The SWSM with superhydrophilic cone channels and a superhydrophobic surface was fabricated by laser etching and surface modification. The droplet jets were observed after the droplet entered the water from the superhydrophilic cone channels. An experimental platform was established to observe the SWSM motion. The effects of the droplet volume and the cone angle on the SWSM motion were investigated based on the experimental platform. The maximum swimming velocity and the swimming distance of the SWSM were 68 mm/s and 78 mm with the superhydrophilic cone angle of 7° and the droplet volume of 35 μl, respectively. Triangular and circular cargoes were transported successfully by controlling the droplets on the superhydrophilic cone channels. In addition, a centrosymmetric SWSM with two superhydrophilic cone channels was designed to achieve rotational motion. The surface energy of the droplets was converted into the mechanical energy of the SWSM without external power. The reported self-propelled mini-robots provide a solution for rainwater harvesting and energy conservation.