Depinning Characteristics Of Two-dimension Active Magnetized Colloids On A Disordered Pinning Substrate

Active colloids have close connection with the formation of Biological self-organization, and Biological self-organization is often formed in non-equilibrium condition. So, investigating the dynamics characteristics of the system is of great importance to explore the formation of the biological self-organization in the non-equilibrium condition.For a long time, physicists believe that spontaneous process makes the system tend to be equilibrium. Therefore, the equilibrium structure is the only ordered state which can be explained by the laws of physics and can be reproduced in experiment,and Boltzmann principle is the only principle that can dominate from disorder to order in physics. However, physicists met with great difficulty when using the Boltzmann’ s order principle to explain the biological order phenomenon. According to the probability point of view( if the emergence of various kinds of molecular events is the same probability, then the self-organization phenomenon is obviously a kind of highly improbable events), the formation of biological order is a highly improbable event, and therefore cannot be explained by Boltzmann’ s order principle.Biology can present order phenomenon not only in the level of biological molecules,but also at all organism levels(such as groups, individual, tissue, cells, molecules,etc.). For example, many leaves, flowers and all kinds of animal fur often present pretty regular patterns. Moreover, biological order not only appears in the spatial domain, like the high order of biological molecules, but also in the time characteristic,like the biological clock. There are inherent regularity in all levels of life movement.There are many examples about the spontaneous formation of macro-ordered structures. For example, heaven street, vortex structure in Jupiter’s atmosphere,beautiful Songhua appeared in egg, bacterial flagellum, Bernard effects, coherent laser beam and chemical wave, etc. These phenomena follow the same principles, i.e.,particles in the system present a long-range consistency and relevance on the macrospace distance or on the time interval, they seem to suffer some sort of unified command to organize themselves to form a macroscopic space-time consistency. The phenomenon of the formation of ordered structures called self-organization phenomena.The formation of self-assembled structure of nanoparticles and mesoscopic level particles has been a hot topic in condensed matter physics. It is also the focus of the field of soft matter and biological field.Recently, cluster dynamics of activity colloidal particles has been studied extensively. Active system contrasts with the passive system, and many researches about self-organization is emphasis on the equilibrium of system self-organization. But, the study of self organization in non equilibrium systems is also very important. Non-equilibrium self-organization is through the consumption of energy to achieve the characteristic order, such as the random organization of shear colloid suspension and active vortex. Based on the energy injection mechanism, the movement of particles can be divided into two categories, one is that the particles is driven by electric field, magnetic field and thermodynamics flow field, etc., the exerted external field force or torque on particles, or directly on the solid-liquid, liquid-liquid surface. Another is that particle is driven by internal chemical reaction or ultraviolet radiation.Using Langevin molecular dynamics simulations, in this thesis we have numerically studied the non-equilibrium dynamics of two-dimensional active magnetized colloids on a disordered pinning substrate. Firstly, the depinning characteristics of active system and passive system have been investigated systematical with the changing substrate strength. Active system generally refers to the collection of particles, single particle in the system through the consumption of energy to achieve self-assembly movement. Inactive system is also called passive system, and it is relative to the active system. We found that in the passive system,with an increase in the pinning strength of substrate, the critical pinning force is gradually increases, Whereas, in the active system, with an increase in the pinning strength of substrate, peak effect appears in the critical pinning force.Secondly, this paper studies the depinning characteristics of active system and passive system are studied with the changing interaction strength between colloidalparticles. We found that, with an increase in the interaction strength between particles,the critical pinning force gradually decreases.Finally, we have studied the influence of L-J potential strength to the depinning characteristics. We found that the depinning property is evidently affected within a range of the L-J potential, i. e., 0.08 to 0.58.There are self-propelled interaction between active colloidal particles, colloidal particles are through this self-propelled interaction to form the limited size of the clusters. Non-equilibrium active system shows richer phases. We believe that this study will be helpful for solving problems encountered in material science, biological chemistry and condensed matter physics.