Mechanics of amorphous and polymeric matter

本研究计划运用理论和电脑模拟来探索结构无序和远离平衡的高分子物质的力学行为。无序材料的例子包括无定形金属、许多软玻璃，如泡沫、糊状物、乳剂和致密的胶体悬浮液或细胞组件。在这些材料中，变形机制比在晶体固体中了解得少得多，在晶体固体中，作为塑性流动载体的缺陷运动很容易识别。现有的工程描述往往侧重于平均行为，当波动变得很大时就会失效。在这里，我们寻求对非晶金属和屈服应力流体流变行为的微观起源的基本理解，以便能够调整和改善它们的机械性能。当材料屈服时，控制应力和应变速率的流变流动规律不仅是强非线性的，而且隐含着空间非局部协同性。这种协同作用导致变形局部化为剪切带，这目前阻碍了金属玻璃的广泛应用。在这里，我们将粒子尺度上的分子模拟定量地与介观和连续尺度上的更粗略的描述联系起来，以构建无定形物质塑性流动的预测统计理论。******此外，我们将创新新的计算工具来模拟具有瞬态（即物理）交联的纳米结构大分子网络的结构和力学。常见的例子是由共聚物或半结晶聚合物形成的热塑性弹性体，它们具有广泛的消费和工业应用。我们将通过连接不同长度和时间尺度的分子模拟来分析链水平的变形过程，以开发和测试可以将分子结构转化为中尺度形态的理论模型，然后预测宏观尺度的性质。一个重要的部分将是通过物理机制（如氢键或相分离）来研究具有自修复能力的软弹性体的断裂。我们将计算基于热敏（co）聚合物的智能（刺激响应）水凝胶的结构、粘弹性和断裂，这些水凝胶可以应用于致动器、人工组织或医疗植入物。在代表活细胞的细胞骨架网络的半柔性生物水凝胶模型中，我们将探索对局部扰动的弹塑性响应的传播，这被认为在细胞信号传导中起重要作用。阐明弹性体和水凝胶的受控组装和响应途径，使新材料的计算信息加速设计和更好地理解活性物质的新特性。*****

This research program employs theory and computer simulations to explore the mechanical behavior of structurally disordered and polymeric matter far from equilibrium. Examples of disordered materials include amorphous metals, many soft glasses such as foams, pastes, emulsions, and dense colloidal suspensions or cell assemblies. In these materials, deformation mechanisms are much less understood than in crystalline solids, where the motion of defects as carriers of plastic flow is easily identified. Existing engineering descriptions tend to focus on average behavior and fail when fluctuations become large. Here we seek a fundamental understanding of the microscopic origin of the rheological behaviour of amorphous metals and yield stress fluids in order to be able to tune and improve their mechanical properties. The rheological flow rules governing stress and strain rate are not only strongly nonlinear, but also imply spatial nonlocal cooperativity when the material yields. This cooperativity leads to the localization of deformation into shear bands, which currently precludes widespread applications of metallic glasses. Here, we will connect molecular simulations on the particle scale quantitatively with coarser descriptions on mesoscopic and continuum scales to construct a predictive statistical theory of plastic flow of amorphous matter. ******Additionally, we will innovate new computational tools for simulating structure and mechanics of nanostructured macromolecular networks with transient (i.e. physical) crosslinks. Common examples are thermoplastic elastomers formed out of copolymers or semicrystalline polymers, which have widespread consumer and industrial applications. We will analyze deformation processes at chain level with molecular simulations connecting different length and time scales in order to develop and test theoretical models that can translate molecular structure into mesoscale morphology, and then predict macroscale properties. An important part will be to investigate breaking of soft elastomers with self-healing capabilities via physical mechanisms such as hydrogen bonds or phase separation. We will compute the structure, viscoelasticity, and fracture of smart (stimuli responsive) hydrogels based on thermosensitive (co)polymers, which find applications as actuators, artificial tissue or medical implants. In a model for semiflexible biological hydrogels representing the cytoskeletal network of living cells, we will explore the propagation of the elastoplastic response to local perturbations, which is believed to play an important role in cell signaling. Elucidating pathways to controlled assembly and response of elastomers and hydrogels enables computationally-informed accelerated design of new materials and better understanding of the emerging properties of active matter.*****