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...