Transport of self-propelled particles in a two-dimensional (2D) separate channel is investigated in the presence of the combined forces. By applying an ac force, the particles will be trapped by the ...separate walls. A dc force produces the asymmetry of the system and induces the longitudinal directed transport. Due to the competition between self-propulsion and the combined external forces, the transport is sensitive to the self-propelled speed and the particle radius, thus one can separate the particles based on these properties.
We numerically investigate the ratchet transport of mixtures of active and passive particles in a transversal asymmetric channel. A big passive particle is immersed in a 'sea' of active particles. ...Due to the chirality of active particles, the longitudinal directed transport is induced by the transversal asymmetry. For the active particles, the chirality completely determines the direction of the ratchet transport, the counterclockwise and clockwise particles move to the opposite directions and can be separated. However, for the passive particle, the transport behavior becomes complicated, the direction is determined by competitions among the chirality, the self-propulsion speed, and the packing fraction. Interestingly, within certain parameters, the passive particle moves to the left, while active particles move to the right. In addition, there exist optimal parameters (the chirality, the height of the barrier, the self-propulsion speed and the packing fraction) at which the rectified efficiency takes its maximal value. Our findings could be used for the experimental pursuit of the ratchet transport powered by chiral active particles.
Abstract
The demixing and sorting strategies for chiral active mixtures are crucial to the biochemical and pharmaceutical industries. However, it remains uncertain whether chiral mixed particles can ...spontaneously demix without the aid of specific strategies. In this paper, we investigate the demixing behaviors of binary mixtures in a model of chiral active particles to understand the demixing mechanism of chiral active mixtures. We demonstrate that chiral mixed particles can spontaneously demix in motility-induced phase separation (MIPS). The hidden velocity alignment in MIPS allows particles of different types to accumulate in different clusters, thereby facilitating separation. There exists an optimal angular velocity or packing fraction at which this separation is optimal. Noise (translational or rotational diffusion) can promote mixture separation in certain cases, rather than always being detrimental to the process. Since the order caused by the hidden velocity alignment in this process is not global, the separation behavior is strongly dependent on the system size. Furthermore, we also discovered that the mixture separation caused by MIPS is different from that resulting from explicit velocity alignment. Our findings are crucial for understanding the demixing mechanism of chiral active mixtures and can be applied to experiments attempting to separate various active mixtures in the future.
Rectified transport of active ellipsoidal particles is numerically investigated in a two-dimensional asymmetric potential. The out-of-equilibrium condition for the active particle is an intrinsic ...property, which can break thermodynamical equilibrium and induce the directed transport. It is found that the perfect sphere particle can facilitate the rectification, while the needlelike particle destroys the directed transport. There exist optimized values of the parameters (the self-propelled velocity, the torque acting on the body) at which the average velocity takes its maximal value. For the ellipsoidal particle with not large asymmetric parameter, the average velocity decreases with increasing the rotational diffusion rate, while for the needlelike particle (very large asymmetric parameter), the average velocity is a peaked function of the rotational diffusion rate. By introducing a finite load, particles with different shapes (or different self-propelled velocities) will move to the opposite directions, which is able to separate particles of different shapes (or different self-propelled velocities).
A two-cluster system with a bistable potential is constructed in one-dimensional channels. Using molecular dynamics and Monte Carlo methods, we study the collective diffusion properties of the ...bistable cluster system. It is shown that the internal structure of the bistable cluster can greatly influence the diffusion behavior, which is different from simple particle systems. The collective diffusion coefficients of two states can differ by two orders of magnitude. An explanation is found from the distance distribution between two clusters. This study provides theoretical guidance for understanding the particularity of complex active structures in diffusion behavior. If the results are extended to active matter, it can be understood that the active matter can regulate the diffusion ability by changing its own morphology or stability.
Graphical abstract
In this manuscript, we have investigated the effects of complex structures on collective diffusion behavior in one dimensional channels as the followings: (1) The collective diffusion coefficient of bistable cluster depends strongly on the internal structure of the cluster. If this is true, it means that the previous simplification of a multi-particle system should be readdressed to new discussions. (2) The influence of cluster bistability on the collective diffusion coefficient varies by two orders of magnitude, just like a switch “on and off”. Assuming that the cluster is an active matter that can adjust its form, then controlling the transport of active matter will be possible.
Abstract
The solid–liquid transition of biological tissues is numerically investigated in the presence of Ornstein–Uhlenbeck noise. We demonstrate that the melting scenario of the system is ...controlled by three parameters: temperature, the persistence time that controls the nonequilibrium properties of the system, and the target shape index that characterizes the competition between cell–cell adhesion and cortical tension. An increase in the persistence time always causes the system to transition from disordered (liquid state) to ordered (solid state). For stiff cells (small target shape index), on increasing temperature, the system undergoes the first order melting for short persistence time, while it undergoes a continuous solid–hexatic transition followed by a discontinuous hexatic–liquid transition for long persistence time. For soft cells (large target shape index), the melting always occurs via a continuous solid–hexatic transition followed by a discontinuous hexatic–liquid transition and the parameter range where the hexatic phase occurs increases with the persistence time. These behaviors are confirmed by the evolution of the density of topological defects. The phase diagrams of the system are also presented based on three parameters (temperature, the shape index, and the persistence time). Our study may contribute to the understanding of melting in two dimensional systems with many-body interactions and deformable particles.
PDF
