Bubbles are widely used by animals in nature in order to fulfill important functions. They are used by animals in order to walk underwater or to stabilize themselves at the water/air interface. The main aim of this work is to imitate such phenomena, which is the essence of biomimetics. Here, bubbles are used to propel and to control the location of Janus particles in an aqueous medium. The synthesis of Janus SiO2-Ag and polystyrene-Ag (PS-Ag) particles through embedment in Parafilm is presented. The Janus particles, partially covered with catalytically active Ag nanoparticles, are redispersed in water and placed on a glass substrate. The active Ag sites are used for the splitting of H2O2 into water and oxygen. As a result, an oxygen bubble is formed on one side of the particle and promotes its propulsion. Once formed, the bubble-particle complex is stable and therefore, can be manipulated by tuning hydrophilic-hydrophobic interactions with the surface. In this way a transition between two- and three- dimensional motion is possible by changing the hydrophobicity of the substrate. Similar principles are used in nature. The ladybird beetle (Coccinellidae) can walk on solid substrates underwater due to bubbles entrapped under a hair-like structure in its legs. Other animals such as the purple snail (Janthina janthina) use stable bubbles in order to float at the air/water interface of the ocean. Both mechanisms are based on hydrophobic-hydrophilic interactions, minimization of surface tension, and buoyancy. Mimicry of these principles is used to propel and localize Janus particles in water.
- Janus particles