Bubble-Enabled Underwater Motion of a Light-Driven Motor

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.