Self-Propelled Motion of a Camphor Disk on a Nervonic Acid Molecular Layer and Its Dependence on Phase Transition.

We studied the self-propelled motion of a camphor disk placed on water developed with a nervonic acid molecular layer to investigate the dependence of types of motion on the properties of amphiphilic compounds. The surface pressure (Π) versus area (A) isotherm exhibited a transition point corresponding to a phase transition between the fluid (F) and fluid/condensed (F/C) phases of nervonic acid. The type of motion was determined by not only the surface pressure of the nervonic acid molecular layer but also the phase, either F or F/C. When the temperature of water was varied through the phase transition temperature Tp40 (∼23 °C), with an area of 40 Å2 per nervonic acid molecule in the molecular layer, no motion and oscillatory motion were observed reversibly above and below Tp40, respectively. Our results suggest that the features of camphor motion depend on not only the surface pressure but also the nature of the phase in the nervonic acid molecular layer.