Surface-energy ratchet motor with geometrical symmetry driven by biased random walk
Scientific Reports volume 14, Article number: 16619 (2024 ) Cite this article
A geometrically symmetric gear with asymmetric surface wettability exhibits one-way spin on a vibrating water bed. On the side face of the gear, a parafilm was coated to create asymmetry in the surface energy. The gear shows fluctuations in both directions within a shorter timescale; however, for a longer timescale, the gear exhibits a one-way spin. This unique motion is generated by a stochastic process with a biased driving force produced by the interaction between the vibrating water surface and the side face of the gear. This new model resembles an active Brownian ratchet. Until now, most ratchet motors, which obtain regular motion from nonthermal fluctuations, utilize a geometrical ratchet structure. However, in this study, the surface energy forms a ratchet that rectifies the noisy motion.
The spontaneous rectification of noisy motion to a regulated form using a ratchet mechanism is a fascinating energy-conversion system1,2,3,4. In biological systems, a Brownian ratchet has been proposed to understand the mechanism of molecular motors, where the periodically varying potential produced by a chemical reaction is considered to rectify the thermal motion of molecules to generate net transport5,6,7,8,9,10,11,12,13. The pattern of the potential field periodically changes between uniform and ratchet shapes, resulting in directed transport. Thus, rectification generates mechanical work. The efficiency of energy conversion is reported to be higher in vivo than in vitro14,15,16. Physiological chemical reactions in vivo modulate thermal motion to generate nonthermal fluctuations, which may be crucial for the ratchet mechanism. Energy conversion from nonthermal agitation to a mechanically utilized form has attracted significant attention in the field of nonlinear science1,2,3. This scientific trend has inspired ratchet motor studies that extract regulated motions from nonequilibrium fluctuations.
