Transient Network Theory: Bridging Molecular Mechanisms to the Viscoelasticity of Soft Polymers

将大量分子组织成材料的能力可以打开制造动态材料或软机器的大门，从而促进国家的健康、繁荣和福利；甚至通过促进新兴的软机器人领域来确保国防安全。这类材料在自然界中经常以瞬时聚合网络的形式存在，它们是肌肉收缩以及生物组织自我修复和适应的根源。尽管类似的分子网络可以在实验室中合成，但它们的性能仍然远远落后于生物网络；这增加了对更好的理论理解和实验控制的需要。该项目将提供一条途径，从根本上了解此类聚合物网络的组织和动态如何能够导致目标明确的新反应。它将通过弥合我们对单个分子行为的理解和对整个网络的理解之间的差距，促进软物质科学的进步，不仅使我们能够对生物聚合物有一个基本的了解，而且还可以提高我们控制合成材料的能力。该项目还将围绕高中“未来材料和生物灵感”的概念，加强本科课程，以及通过社交媒体传播科学知识，开发一个教育项目。从基本观点来看，该项目将支持暂态网络理论的发展，该理论将在统计学意义上描述基于分子过程的暂态聚合物网络的时间演化，如链分离、声誉或扩散。超越唯象粘弹性模型，统计力学中的关键概念将被用来获得许多聚合物链之间的瞬时分子相互作用与网络的时间依赖响应之间的更清晰的联系。该项目带来了三个关键贡献：(A)对分子过程与流变学、弹性和能量耗散之间的关系有了新的基本理解；(B)能够产生关于动态聚合物的新假设，并从生长、抗断裂和自我修复方面探索其宏观结果；以及(C)描述介于固体和流体之间的软材料的极端变形的新的连续介质框架。将引入基于有限元的计算方法来解决研究理论，并用于研究和表征合成聚合物和生物聚合物的粘弹性响应的内部结构。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The ability to organize large populations of molecules into materials can open the door to making dynamic materials or soft machines, thus advancing the national health, prosperity, and welfare; and even securing the national defense by facilitating the emerging area of soft robotics. Such materials are often found in nature in the form of transient polymeric networks which are at the source of muscle contraction as well as self-healing and adaptation in biological tissues. Although similar molecular networks can be synthesized in the laboratory, their performance still lags far behind their biological counterparts; raising the need for a better theoretical understanding and experimental control. This project will provide a route to fundamentally understand how the organization and dynamics of such polymer networks can lead to a well-targeted emerging response. It will promote the progress of soft matter science by bridging the gap between our understanding of the behavior of a single molecule and that of an entire network, not only enabling a fundamental understanding of bio-polymers, but also in improving our ability to control synthetic materials. The project will also develop an educational program around the concept of "materials of the future and bio-inspiration" in high-schools, the enhancement of undergraduate curriculum, and dissemination of scientific knowledge through social media.From a fundamental viewpoint, this project will support the development of a transient network theory that will describe, in a statistical sense, the time evolution of a transient polymer network based on molecular processes such as chain detachment, reputation, or diffusion. Going beyond phenomenological viscoelastic models, key concepts in statistical mechanics will be used to obtain a clearer connection between transient molecular interactions between many polymer chains and the time-dependent response of the network. The project brings three key contributions: (a) a new fundamental understanding of the relation between molecular processes and rheology, elasticity and energy dissipation; (b) the ability to generate new hypotheses regarding dynamic polymers and explore their macroscopic outcome in terms of growth, fracture resistance, and self-healing, and (c) a new continuum framework to describe the extreme deformation of soft materials whose behavior lies between that of solids and fluids. A computational methodology based on finite elements will be introduced to solve the research theory and used to study and characterize the viscoelastic response of synthetic and biopolymers in terms of their inner structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.