Orientation of active particles in gradient fields

Abstract

We used non-equilibrium molecular dynamics simulations to investigate the effects of the orientation of dumbbell-shaped active particles. Self-driven dumbbell particles are situated between two particle reservoirs connected by a channel. By setting different environmental temperatures or particle concentrations in the two reservoirs, a non-equilibrium state with a temperature or concentration gradient is induced in the channel. It is found that the magnitude of the orientation of the active particles is directly proportional to the strength of the gradient field. The direction of the orientation is in line with the temperature gradient but opposite to the concentration gradient. Moreover, the orientation of active particles is also proportional to the self-propulsion force, while Brownian particles do not exhibit any orientation. The length of the dumbbell particle also has an impact on its orientation. When the spacing is zero, resulting in circular active particles, the orientational effect disappears. Additionally, we explored the potential limitations of traditional statistical mechanics methods in self-propelled particle systems. Our research contributes to a deeper understanding of the relationship between self-propulsion forces and the orientation of active particles.

Graphical abstract

Using non-equilibrium molecular dynamics, we have conducted a thorough investigation into the intricate relationships governing the orientation of active particles. Notably, the orientation aligns with the temperature gradient but opposes the concentration gradient, offering a unique insight into the behavior of these particles under varying conditions. Furthermore, we observed a positive correlation between the self-propulsion force of active molecules and their orientation. This correlation underscores the significance of self-propulsion in dictating the orientational behavior of these particles, which is absent in Brownian particles.