Speaker
Abstract
Understanding the flow behaviors of supercooled liquids presents a major challenge in liquid-state physics due to the strong nonlinearity and rich phenomena. To unravel this complexity, we introduce the concept of local configurational relaxation time \tau_\rm{LC}, which allows us to embody the solid-liquid duality, proposed by Maxwell for phenomenologically describing materials’ response to external load, at the particle level. The spatial distribution of \tau_\rm{LC} in flow is heterogeneous. Depending on the comparison between the local mobility measured by \tau_\rm{LC} and the external shear rate, the shear response of local regions is either solidlike or liquidlike. In this way, \tau_\rm{LC} plays a role similar to the Maxwell time. By applying this microscopic solid-liquid duality to different conditions of shear flow with a wide range of shear rates, we describe the emergence of shear thinning in steady shear and predict the major characteristics of the transient response to start-up shear. Furthermore, we reveal a clear structural foundation for \tau_\rm{LC} and the solid-liquid duality associated with it by introducing an order parameter extracted from local configuration. Thus, we establish a framework that connects microscopic structure, dynamics, local mechanical response, and flow behaviors for supercooled liquids. Finally, we rationalize our framework in terms of activations from energy basins that are facilitated by shear. This model illustrates how local structure, convection, and thermal activation collectively determine \tau_\rm{LC}. Notably, it predicts two distinct response groups, which well correspond to the microscopic solid-liquid duality.
摘要
过冷液体展现出丰富的物理现象和非线性流变响应，理解其流动行为是液体物理学中的一项重大挑战。为此，我们引入了局域构形松弛时间 \tau_\rm{LC} 的概念。\tau_\rm{LC} 在空间上呈不均匀分布；通过比较其所表征的局部松弛速率与外加剪切速率，我们发现局部区域的剪切响应可呈现类固或类液两种形式——在此意义下，\tau_\rm{LC} 与麦克斯韦时间相类似。基于这种微观固液二元响应，我们系统考察了不同剪切速率下的流动行为，不仅能描述宏观剪切变稀的起源，还成功预测了启动剪切过程中瞬态应力演化的主要特征。进一步，我们从局部构形中提取出结构序参量，为 \tau_\rm{LC} 及相关的固液二元响应建立了微观结构基础，从而构建起一个贯通过冷液体微观结构、局域动力学、局域力学响应与宏观流动行为的框架。最后，我们基于势垒激发模型对该框架进行了建模，阐明了局部结构、流动与热激发如何共同调控 \tau_\rm{LC}；该模型可预测出两类不同响应的粒子，与实际观察到的微观固液二元响应相吻合。
| 关键词 | 过冷液体；流变；动态不均匀；黏弹性； |
|---|---|
| Keywords | supercooled liquids; rheology; dynamic heterogeneity; viscoelasticity; |
