Propulsion of cruising boats by thrust forces of bubbles released from nanotextured nickel-plated heaters

Bubble-driven vehicles (or microboats) are used in fields related to sensors, lab-on-a-chip systems, robotics, drug delivery, nanosurgery, and electricity generation. In these vehicles, the bubble recoil force is generally used as a means of propulsive thrust, where the bubbles are mainly generated through catalytic reactions, acoustic oscillations, and photothermal effects. Herein, we used Joule heating resulting in vaporization to produce bubbles, through which both thrust and recoil forces were generated. The heating wire was nanotextured with nickel nanocones to afford numerous nucleation sites, which, in turn, significantly increased the bubble generation and propulsive thrust. A recoil force was induced once the bubbles were ejected from the heating wire. Simultaneously, the angled bottom surface of the boat serves as a nozzle by redirecting horizontally backward the fluid flow entrained by the rising bubbles. We demonstrated that the recoil force was lower than the thrust provided by the bubbly flow. Notably, nickel nanotexturing contributed to the enhancement in the total propulsive thrust. Thus, forward, backward, and rotational motions of the cruising boat with rapid maneuverability were demonstrated in this work.