Insights into characteristic motions and negative chemotaxis of the inanimate motor sensitive to sodium chloride

Inanimate motors, driven by the difference in surface tension, provide platforms for studying the physics of characteristic motion and mimicking the complex behaviors of biological systems. However, it is challenging to endow inanimate motors with high autonomy, with an emphasis on simulating the behavior of living organisms in response to external stimuli. Herein, by applying sodium chloride (NaCl) as an external stimulus, we achieve the regulation of motion mode and chemotaxis in a self-propelled camphor system. We present a comprehensive surface/interface understanding of motion bifurcation with the increase of concentration NaCl, i.e., continuous motion to no motion via oscillatory motion. The features of motions (the speed and frequency) and the mechanisms are elucidated depending on the concentrations of NaCl and sodium dodecyl sulfate (SDS). Furthermore, the characteristic motion and chemotaxis to the salt stimulus are correlated to the dynamic breaking/reforming of the surface tension balance and gradient-type distribution phenomenon triggered by dynamic camphor dissolution, surfactant adsorption /diffusion and camphor-surfactant interaction. This work sheds light on the typical motions of inanimate motors and scrutinizes the synergy between dual additives, which will boost the design of advanced self-propelled systems with nonlinear characteristic motion.