Abstract:
The present thesis entitled “Transport properties of artificial micro-swimmers and related non equilibrium phenomenona” deals with an important class of artificial micro-swimmers (self-propelled Janus particles) which are capable of autonomous propulsion by extracting energy out of fluctuations. Based on the numerical analytical modeling we address the following issues- 1)dynamics of fast moving particles in the presence of the slower moving one 2) effect of flow field on the diffusion of self-propelled particles 3) diffusion mechanism when transient effects are important, and 4) diffusion in various types of confined structures. The work is carried out at the Department of Chemistry,Presidency University, Kolkata 700073 India, under the supervision of Dr. Pulakkumar Ghosh The present thesis addressed the above mentioned issues based on the simulation of dynamics of Janus particles. The thesis is organized as follows. In Chapter 1, we present the introduction of self-propelled Janus particles and briefly describe significance of our works in the context of previous works in this field as well as applications in nanotechnology and medical sciences. Chapter 2, presents transport properties of Janus particles in a binary mixture of two kinds of swimmers in the under-damped limit. Based on the numerical simulation we show the presence of strong Janus particles considerably improves velocity distribution of weak particles. In the Chapter 3, we show that even in the absence of inertia, motility can transfer from weak to strong particles in the binary mixture. This has been confirmed by studying how effusion of weak particles changes by the presence of passive particles. Chapter 4, presents diffusion of selfpropelled Janus particles in the counter rotating convection rolls. We focus on the large Péclet numbers, i.e., for self-propulsion speeds below a certain depinning threshold and weak rototranslational fluctuations. In this limit the particle undergoes asymptotic normal diffusion with diffusion constant proportional to the square root of its diffusion constant in the absence of flow. We model Chirality effects in the propulsion mechanism assuming a tunable applied torque which induce particle jumping between adjacent convection rolls. The jumping mechanism among adjacent convection rolls can be identified by an excess diffusion peak. In the Chapter 5, we explore interplay between inertial relaxations to the time correlated selfpropelled motion in confined structures. This issue is potentially important as most of the novel nano-technological applications of Janus particles involve diffusion through different types of confined structures v where inertial impact as well as self-propulsion. We address this issue and show that inertial impact is important in the experimentally accessible situations for both selfpropelled and passive particles. In Chapter 6, we present a summary of our works and possible future
