pH-sensitive self-motion of a solid scraping on an aqueous phase

The self-motion of a solid scraping at an air/water interface was investigated. The self-motion of a camphoric acid scraping changed characteristically depending on the pH of the aqueous phase. With an acidic aqueous phase, the camphoric acid scraping maintains a fairly constant velocity. At neutral pH, intermittent motion was observed. These characteristic motions are discussed in relation to the surface free energy which results when the camphoric acid layer diffuses from the scraping. The nature of the diffusion of the camphoric acid layer at the water surface could be observed by adding CaSO4 powder. These results imply the realization of chemomechanical energy transduction under isothermal conditions.