Gas generation due to photocatalysis as a method to reduce the resistance force in the process of motors motion at the air-liquid interface

Abstract

Hypothesis: The problem of the development of miniature motors able to move on the air-liquid interface at low Reynolds numbers is a crucial challenge due to dominating role of viscous force. To solve this problem the chemical generation of gas can be used. Generated gas pushes liquid out from the surfer surface, so the resistance force is reduced.

Experiments: Surfer composed of TiO₂ nanoparticles and ferromagnetic cobalt microparticles moves at the interface of an aqueous solution of hydrogen peroxide under the action of magnetic force. After irradiation with UV or visible light, the gas cavern is formed at the surfer surface due to photo-catalytic decomposition of hydrogen peroxide. As a result, the area of surfer contact with liquid is reduced.

Findings: The resistance force acting on the surfer is reduced due to the liquid pushing out from the surfer surface. This effect is strengthened with the increase in the intensity of gas generation. The resistance force is increased when increasing the liquid viscosity or using a surfactant. The proposed method allows control of the velocity of the motors in a rather wide range by changing the gradient of the magnetic field and parameters of light.

Keywords: Bubbles; Emulsion; Foam; Interface; Motors; Nanoparticles; Photocatalytic materials; Resistance force.