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Spontaneous Directional Motion of Shaped Nanoparticle

In nanoscale space and pico- to nanoseconds enormous physical, chemical and biological processes take place, while the motions of involved particles/molecules under thermal fluctuations are usually analyzed using the conventional theory of diffusive Brownian motion based on both sufficiently long time averaging and assumptions of spherical particle shapes. Here, using molecular dynamics simulations, we show that asymmetrically shaped nanoparticles in dilute solutions possess spontaneous directional motion of the center of mass within a finite time interval. The driving force for this unexpected directional motion lies in the imbalance of the interactions experienced by their constituent atoms during the orientation regulation at timescales before the onset of diffusive Brownian motion. Theoretical formulae have been derived to describe the mean displacement and the variance of this directional motion. Our study potentially takes an important step towards establishing a complete theoretical framework for describing the motions of variously-shaped particles in solutions over all timescales from ballistic to diffusive regime.