报告题目：Shear Banding and Entanglement in Polymer Melts

报 告 人：王振纲教授（美国加州理工学院）

报告时间：2025年9月15日上午9：30

报告地址：五山校区科技园2号楼324报告厅

报告邀请人：周嘉嘉教授

邀请单位：前沿软物质学院

报告摘要：

We use molecular dynamics simulations to investigate the origins of shear banding in entangled polymer melts. Under steady shear, the flow exhibits a pronounced stress plateau where the fluid separates into coexisting shear bands. We find strong correlation in the location of the shear bands between different shear rates starting from the same microstate configurations at equilibrium, which suggests the importance of the inherent structural heterogeneity in the entangled polymer network for shear banding. To characterize the topological entanglements, we propose a novel primitive path analysis (FT-PPA) that characterizes entanglement types, revealing populations of multiple (MuEs) and intervening (InEs) entanglements with distinct lifetimes. Crucially, we find a strong correlation between the center position of the fast shear band and the location of the minimum of the spatial distribution of MuEs and InEs in the gradient direction prior to the application of shear.  This provides direct evidence that shear banding is not a random instability but is dictated by pre-existing spatial variations in the topological network. Furthermore, within the stress plateau, the shear rate in the fast band scales with the imposed rate, in contradiction to the lever rule. Our work suggests that the mean-field, single-chain view of entanglements is insufficient to predict flow instability, necessitating a theory that accounts for spatial correlations and entanglement types. 

个人简介：

王振纲教授 1982 年毕业于北京大学化学系。1987 年获芝加哥大学博士。之后分别在ExxonMobil公司和加州大学洛杉矶分校做博士后研究。1991年受聘于美国加州理工学院化学与化工学部，现为 Dick and Barbara Dickinson 讲座教授。

王振纲教授是国际知名的高分子和软物质理论物理学家。主要研究领域涉及高分子溶液、混合物和共聚物的热力学与动力学；表面和界面；液晶态、胶体和凝胶；软物质体系的静电相互作用；DNA 和 RNA的生物物理和病毒自组装；生物膜物理等。2001 年当选美国物理学会会士。2008 年获美国加州理工学院最高教学奖Richard P. Feynman 奖。2025年当选美国工程院院士。