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Flocking Behavior of Self Propelled Particles Under Confinement

Khatami, Maryam | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50432 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Ejtehadi, Mohammad Reza; Seyed Reihani, Nader
  7. Abstract:
  8. Studying the interaction of active particles with walls and obstacles has a great importance for practical purposes. Using this knowledge, it is possible to control the motion of active particles in different environments.Experimental evidences show that after encountering with a wall, most of the active particles slide along the wall for some time and then detach in a certain direction, independent of their incoming angle. This special collision is considered to guide, sort or trap active particles.In this dissertation, using Brownian dynamics simulations and theories, we study how different selfpropelled particles and walls influence each other. We explore the behavior of two important self-propelled particles, namely active Brownian particles and run-and-tumble particles, inside complex geometries. While many experiments report similar interaction of these two particles with simple geometries, here we show that they behave completely differently in nested mazes. Therefore nested mazes are excellent devices to separate these types of self-propelled particles from each other and from passive Brownian particles. An important advantage of this separation method is that the proposed devices do not need any chemical or biological agents. In addition, we study the behavior of chiral self-propelled swimmers enclosed inside a deformable vesicle. The vesicle deforms as a result of interaction with active particles and its deformation influences from the chiral nature of the particles. Depending on the swimmers density and their chirality frequency, the vesicle demonstrates rich variety of translational and rotational motions, including random walk, circular and ballistic motion, run-and-tumble and chiral active motion. Furthermore by considering both dumbbell swimmers and self-propelled rods, we investigate the effect of swimmer shapes on the dynamics of the system. It reveals that the detailed shape of the swimmers strongly affect both the vesicle deformation and its motility behavior. Eventually, we study the collective motion of self-propelled particles interacting with a star like geometry. This geometry performs similar to a trap and captures the active particles inside it. In experiments, these devices could be fabricated using microfabrication techniques and explored experimentally.In conclusion, the self-propelled particles and the geometries affect each other in a complex manner and the behavior of the whole system depends on the characteristics of the geometry as well as the shape or swimming strategy of self-propelled particles. Results of these studies improve the knowledge and control over the motion of self-propelled particles in natural or laboratory environments
  9. Keywords:
  10. Active Matter ; Collective Behavior ; Self-Propelled Particles ; Run-and-Tumble Particles ; Chiral Active Particle ; Flexible Polymer

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