Phase Transition And Transport Of Active Colloidal Mixtures

Active matter consists of self-propelled units that are capable of taking up energy from their environment and converting it into directed locomotion.Active matter is widely found in nature,including molecular motors,bacterial solutions,or animal groups,and ranges in size from micrometers to meters.Due to inherently out-ofequilibrium features in each unit,they feature a series of novel structural and dynamic phenomena that are not attainable by matter at thermal equilibrium.Many physical problems need to be tackled in active matter.Here are two representative issues: understanding the emergence of collective behavior of active matter and extending the significant physical concepts in passive fields to active systems.The research in this thesis will focus on the following issues by Brownian dynamics simulations:In the first part,the collective behavior of chiral active systems is less studied than linear active systems.In addition,the chiral active fluid system has odd viscosity and edge flow,which will lead to a new non-equilibrium structure and collective dynamic behavior.Therefore,we study the non-equilibrium structure and collective dynamic behavior of the active rotor mixtures.The phase behavior of active rotor mixtures is investigated,the microscopic mechanism behind the phase separation is clarified,and the phase separation of active rotor mixtures is induced by odd viscosity.In the second part,particle diffusion in active fluids has gradually attracted the extensive attention of researchers.Passive particles exhibit enhanced diffusion and novel phase separation in active fluids of active rotors.In the past research on active rotors,most systems were single-component,and the dual-component or multicomponent systems were rarely considered.We further study the phase separation of multiple mixtures composed of active rotors and passive particles,and we find some novel structural and dynamic behaviors.In the third part,due to the lack of systematic thermodynamic theory to describe active matter,it has become an important research direction to extend the thermodynamic concept in passive fields to active systems in recent years.Previous studies have promoted representative thermodynamic quantities such as pressure,temperature,and depletion force.However,some atypical thermodynamic concepts,such as the concept of non-equilibrium thermodynamics under the linear response framework,are rarely introduced to active systems.Phoresis is an important nonequilibrium physical effect.We extend the basic physical concepts of thermophoresis and diffusiophoresis in a hot bath to the active bath composed of active matter.Active Brownian particles considering the interaction force were used to explore the active thermophoresis and active diffusiophoresis,and the directional transport of passive colloidal spheres was realized.