A Multi-engine Marangoni Rotor with Controlled Motion for Mini-Generator Application

Abstract

Marangoni rotors are smart devices that are capable of self-propulsive motions based on the Marangoni effect, namely interfacial flows caused by a gradient of surface tension. Owing to the features of untethered motions and coupled complexity with fluid, these Marangoni devices are attractive for both theoretical study and applications in biomimicking, cargo delivery, energy conversion, etc. However, the controllability of Marangoni motions dependent on concentration gradients remains to be improved, including the motion lifetime, direction, and trajectories. The challenge lies in the flexible loading and adjustments of surfactant fuels. Herein, we design a multi-engine device in a six-arm shape with multiple fuel positions allowing for motion control and propose a strategy of diluting the surfactant fuel to prolong the motion lifetime. The resulting motion lifetime has been extended from 140 to 360 s by 143% compared with conventional surfactant fuels. The motion trajectories could be facilely adjusted by changing both the fuel number and positions, leading to diverse rotation patterns. By integrating with a coil and a magnet, we obtained a system of mini-generators based on the Marangoni rotor. Compared with the single-engine case, the output of the multi-engine rotor was increased by 2 magnitudes owing to increased kinetic energy. The design of the above Marangoni rotor has addressed the problems of concentration-gradient-driven Marangoni devices and enriched their applications in harvesting energy from the environment.

ON–OFF Control of Marangoni Self‐propulsion via A Supra‐amphiphile Fuel and Switch

“…Results of in situ surface tension changes, rotation velocity of the device, and corresponding simulation have supported the above hypothesis. The new concept of 'supra-amphiphile fuel and switch' provides an active solution to both prolong and control Marangoni self-propulsion with interface chemistry, which is meaningful for miniatured robotics, [6] minigenerators, [7,8] and developing new application scenarios of supra-amphiphiles. [35]…”

“…[1] The driving force is Marangoni flow formed by the surface tension gradient when these insects secret surfactants to reduce the local surface tension. [2] Inspired by such bio-locomotion, researchers have developed artificial Marangoni self-propulsion for applications in intelligent systems including micromotors, [3] soft actuators, [4,5] miniaturized machineries, [6] electricity generation, [7,8] macroscopic supramolecular assembly. [9][10][11][12] In the design of Marangoni self-propulsive systems, several fuel strategies are applied to trigger Marangoni flows including volatile species (e.g., alcohol), [13][14][15][16][17][18] water miscible solvents (e.g., DMF), [19] normal surfactants (e.g., sodium dodecyl sulfate).…”

“…[7] The former two are normally liquids while surfactants could be processed as solid bulk, which is easy to store and re-fill. As for the triggering mechanism, the surface tension gradient could be created by a gradient of either temperature [6,11,20] or chemical composition [5,[7][8][9][10]12] through light irradiation or releasing surfactants, accordingly, both exhibiting advantages/disadvantages. With external energy such as laser source, the thermal Marangoni selfpropulsion could be triggered or stopped by applying or withdrawing laser; meanwhile, heat is dissipated easily to maintain the surface tension gradient.…”

Design and mechanism of photothermal soft actuators and their applications

“…101 Such a boat can carry twice the weight of a wooden block, moving 18.5 cm every 36 s and rotating 153° every 23 s. The photothermal actuator has recently been used for rotational motion, which is utilized to rotate the rotor of an electric nanogenerator for determining sunlight's intensity and generating electrical energy. 102,205 As shown in Fig. 10e, the triboelectric nanogenerator is fabricated by black silicon and copper foam.…”

ON–OFF Control of Marangoni Self‐propulsion via A Supra‐amphiphile Fuel and Switch

“…[1] The driving force is Marangoni flow formed by the surface tension gradient when these insects secret surfactants to reduce the local surface tension. [2] Inspired by such bio-locomotion, researchers have developed artificial Marangoni self-propulsion for applications in intelligent systems including micromotors, [3] soft actuators, [4,5] miniaturized machineries, [6] electricity generation, [7,8] macroscopic supramolecular assembly. [9][10][11][12] In the design of Marangoni self-propulsive systems, several fuel strategies are applied to trigger Marangoni flows including volatile species (e.g., alcohol), [13][14][15][16][17][18] water miscible solvents (e.g., DMF), [19] normal surfactants (e.g., sodium dodecyl sulfate).…”