Transient Reciprocating Motion of a Self-Propelled Object Controlled by a Molecular Layer of a N-Stearoyl-p-nitroaniline: Dependence on the Temperature of an Aqueous Phase

The mode-bifurcation of a self-propelled system induced by the property of a N-stearoyl-p-nitroaniline (C(18)ANA) monolayer developed on an aqueous phase was studied. A camphor disk was placed on a C(18)ANA monolayer, which indicated a characteristic surface pressure-area (pi-A) isotherm. A camphor disk transiently exhibited reciprocating motion at a higher surface density of C(18)ANA. The amplitude of the reciprocating motion increased with an increase in the temperature of the aqueous phase below 290 K, but reciprocating motion varied to irregular motion over 290 K. The temperature-dependent reciprocating motion is discussed in terms of the pi-A curve for C(18)ANA depending on the temperature. The interaction between C(18)ANA molecules was measured by Fourier transform IR spectrometry and Brewster-angle microscopy. As an extension of the study, the trajectory of reciprocating motion could be determined by writing with a camphor pen on the C(18)ANA monolayer.