Self-motion of a camphoric acid boat as a function of pH of aqueous solutions

The mechanism of the self-motion of a camphoric acid boat depending on pH of aqueous solutions was investigated. The self-motion changed depending on pH of the aqueous phase (no motion (pH >10), intermittent motion (pH 6–10), and motion with a constant velocity (pH <6)). The period of intermittence increased with pH. The surface tension in the camphoric acid aqueous solutions with different pH were measured by means of the maximum bubble pressure method and the Wilhelmy method. The camphoric acid concentration-dependencies of the surface tension and the time-variation of the surface tension at different pH were discussed in relation to the manner of self-motion and the nature of the surface active camphoric acid layer. The driving force of the self-motion was estimated by analyzing the self-motion.