Collective behavior of isotropic phoretic disks: from crystalline solids to active turbulence

报告题目：Collective behavior of isotropic phoretic disks: from crystalline solids to active turbulence

报告人： 朱来来  教授（新加坡国立大学）

报告时间：2023年05月15日13：30

报告地点：苏州大学本部物理科技楼101

报告邀请人：张天辉

报告摘要：

Chemically phoretic microswimmers including Janus colloids and isotropic active droplets have recently demonstrated a great potential for self-organizing into active materials. However, the fascinating self-organization of these swimmers remains mysterious owing to an insufficient understanding of their collective dynamics. Here, we conduct large-scale simulations to study a paradigmatic suspension of phoretic swimmers represented by isotropic phoretic disks, explicitly resolving their many-body, long-range hydrochemical interactions. Varying the activity and area fraction of disks, we discover their diverse collective phenomena: formation of crystalline solids resembling Wigner crystals, melting, gas-like chain formation, active transition and turbulence. Notably, changing the activity solely leads to both the solid-fluid phase transition and the fluid's laminar-turbulent transition. We reproduce several experimental observations that have not been unitedly captured by a single model, highlighting the importance of incorporating full physicochemical hydrodynamics. We develop a predictive scaling delineating the solid-liquid transition and further characterize it as a defect-mediated two-step melting scenario via a hexatic phase. For the fluid phase, we identify its oscillatory instability with waves, transition due to wave-breaking clusters of swimmers, and active turbulence manifesting vortices. These progressive scenarios evidence a closer phenomenological resemblance between active and classical fluids in their laminar-turbulent transition then previously demonstrated. Our findings elucidate the collective dynamics of phoretic agents, potentially facilitating the design of active material systems by exploiting non-equilibrium phoretic collectives.

报告人简介：

Lailai Zhu obtained his Ph.D. degree from KTH, Royal Institute of Technology (Sweden) in 2014. He then worked as a postdoc at EPFL (Switzerland) till 2016. After that, he joined the group of Prof. Howard A. Stone at Princeton University as a postdoc. Since 2020, Jan, he joined ME at NUS as a tenure-track assistant professor. He mainly uses theory and simulations to address viscous flow problems involving bio-physics, bio-inspired design and microfluidics. Currently, he is interested in understanding active fluids and active turbulence.