Generic Theory of the Dynamic Magnetic Response of Ferrofluids

报告题目:Generic Theory of the Dynamic Magnetic Response of Ferrofluids

报告人:方昂波副教授   华北水利水电大学

报告时间:2019.11.28 上午900-1000

报告地点:致远楼301

报告邀请人:杭志宏

报告摘要:Ferrofluids belong to an important class of highly functional soft matter, benefited from their magnetically controllable physical properties. Therefore it is of central importance to quantitatively predict the dynamic magnetic response of ferrofluids. Traditional dynamic theories, however, are often restricted to the near-equilibrium regime and/or only apply to nearly ideal ferrofluids that are monodisperse, dilute enough, and weakly interacting. We develop a self-consistent and nonperturbative dynamical mean field theory for typical ferrofluids which are often polydisperse, concentrated, and strongly interacting, possibly driven far from equilibrium.We obtain a general nonperturbative expression for the dynamic magnetic susceptibility, quantitatively agreeing with the spectra obtained from Brownian Dynamics simulations on both mono- and bi-disperse samples. Furthermore, we derive a generic magnetization relaxation equation (MRE) for both mono- and polydisperse ferrofluids by employing the projection operator technique in non-equilibrium statistical mechanics.This MRE is in simple closed form and independent of which model is employed to approximate the equilibrium magnetization curve.Existing models can be recovered as low-order approximations of our generic and nonperturbative MRE. Our theory can play a key role in studying the dynamics of ferrofluids and other polar fluids. It may also have substantial and immediate consequences to various ferrofluid applications.

报告人简介:After completing undergraduate studies in USTC, Dr. Fang went to University of Illinois at Urbana-Champaign and in 2005 obtained his degree of PhD in physics, with dissertation on silicon-based quantum computing.After that he went to Hong Kong University of Science and Technology, first as a postdoc fellow and then a research assistant professor.In Hong Kong he switched his research field to theoretical soft condensed matter, involving liquid crystals, alloy solidification, and interfacial hydrodynamics. In recently years he works on ferrofluids, nanoscale water as well as active fluids.He is now an associate professor at North China University of Water Resources and Electric Power. Quite recently he has made a few significant breakthroughs in ferrofluid dynamics.

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