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

Abstract

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 (<i>A</i>) 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 <i>T</i>_p40 (∼23 °C), with an area of 40 Ų per nervonic acid molecule in the molecular layer, no motion and oscillatory motion were observed reversibly above and below <i>T</i>_p40, 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.