Bubble‐Enabled Underwater Motion of a Light‐Driven Motor

Abstract

This work reports the photothermally driven horizontal motion of a motor as well as the suspending and vertical movements underwater. A motor is designed by attaching two polydimethylsiloxane‐coated oxidized copper foams (POCF) to the two opposite sides of an oxidized copper foam (OCF). When the hydrophobic POCF is immersed in water, it serves as both an air bubble trapper and a light‐to‐heat conversion center. As bubbles grow under photothermal heating, they provide lifting force and result in the revolving motion of the motor. With removal of light illumination, bubbles are cooled by the surrounding water and shrink, and the buoyance is lowered. The resultant force of gravitational force, buoyance, and fluid resistance drives the motor to move forward horizontally. Furthermore, the motors are utilized as oil collectors and oil/water separation is achieved successfully. To effectively control the suspending motion, a polydimethylsiloxane foam doped with carbon black (C‐foam) is designed under the photothermal principle. It is maintained at a certain position underwater by controlling the on/off of light. The vertical motion is also studied and utilized to generate electricity. It is expected that different types of underwater motion will open up new opportunities for various applications including drug delivery, collection of heavy oil underwater, and electricity generation.

Light‐Driven Carbon‐Based Soft Materials: Principle, Robotization, and Application

“…The bubbles can provide sufficient vertical propulsion force for the actuators, providing solutions for the multi‐directional aquatic motions. [ 36,115,117 ] Luan et al. developed a magnet‐coupled porous carbon black‐doped hydrophobic PDMS foam (C‐foam) which can implement underwater movement with the assist of bubbles.…”

“…By adjusting the light power density by a certain amount, such C‐foam could suspend in the water when the buoyancy equaled to the gravity. [ 36 ]…”

“…Owing to the photothermal effect and heat‐to‐work ability, the carbon‐based actuators can convert the light energy into other energies. [ 30,99,36 ] For example, the ink‐PET‐acrylic actuator‐based mill was developed to convert external light energy into rotational energy using light‐triggered blades as shown in Figure a. [ 30 ] When exposed to periodic NIR light, the ink‐PET‐acrylic actuators sequentially bent and unbent to generate air flow and further drove the rotation of the light mill.…”

“…Reproduced with permission. [ 36 ] Copyright 2019, Wiley‐VCH. l–p) The light‐driven carbon‐based actuators can be applied in l) bionic hand and arm, m) bionic plant, n) cargo transfer, o) self‐sensing element, and p) energy transfer applications.…”

Non-biodegradable objects may boost microbial growth in water bodies by harnessing bubbles

“…Using similarly generated oxygen bubbles, Song et al [20] devised a pH-responsive cube that can rise up or sink down in an aqueous environment depending upon the acidity of the medium. Not long ago, Luan et al [21] created a photothermally driven hydrophobic motor where they manoeuvred its buoyancy by expanding and shrinking adhered gas bubbles through intermittent light illumination. In another curious work, Zhang et al [16] fabricated a hydrophobic rocket to achieve its cyclic rising and sinking inside a bacterial fermentation system with an intention to generate electricity through Faraday's Law.…”