Nonlinear Dynamics of Entangled Polymers with Well-controlled Long-chain Branching

本研究旨在探讨如何利用链结构的分子设计来影响纠缠聚合物的非线性动力学。本研究将尝试控制各种聚异戊二烯和聚丁二烯基熔体的长链分支（LCB）结构，并确定LCB熔体与相应的线性熔体在不同大变形条件下的差异。具体目标如下：1)确定各种LCB聚合物的界面屈服特性，并与相应的线性对应物进行对比；2)探索熔体强度如何取决于特定的链结构，例如，每条链的分支点数量；3)检验带LCB的缠结网在大变形时是否会出现应变局部化；4)确定关键的分子结构参数，这些参数定义/决定了内聚力和对大变形的非线性响应；5)研究LCB不同组分或LCB与线性链混合对非线性动力学的影响。为了实现这些目标，将进行简单和单轴扩展，包括启动应变或阶跃应变。在所有情况下，有效的粒子跟踪测速（PTV）观测将是必不可少的和系统的。在剪切的情况下，圆形库埃特剪切室将采用PTV能力。单轴扩展将通过反向旋转双缸装置或Instron实现，其中也将进行原位PTV测量。本研究旨在探索和确定指导性的基本原则，这些原则可能会在更高效和节能的聚合物材料制造中得到应用。这些原则将最终从目前提出的工作中出现，旨在确定聚合物材料的不同分子设计如何影响塑料和橡胶的加工能力。拟议工作的结果应产生对塑料和橡胶工业有价值的明确信息。同时，实验活动有望促进聚合物物理领域的理论发展。更广泛地说，PI计划将这项研究的发现整合到一本教科书中，其中将包括他在该领域贡献的所有关键结果。由于所提议的研究的本质是可视化密集型的，复杂的物理现象可以得到直观的解释，从而为初高中学生提供有吸引力的教育材料，让他们了解科学是如何完成的。作为研究活动的一部分，还与中国科学院长春应用化学研究所开展了一项国际合作，旨在开展计算机模拟，以补充各种拟议的实验。

TECHNICAL SUMMARYThis research aims to probe how molecular design of chain architecture can be employed to affect nonlinear dynamics of entangled polymers. The proposed research will attempt to control the structure of long-chain branching (LCB) in various polyisoprene and polybutadiene-based melts, and determine the differences between melts with LCB and corresponding linear melts under different conditions of large deformation. The specific objectives of the proposed work are as follows: 1) Determine interfacial yielding characteristics of the various LCB polymers to contrast with corresponding linear counterparts; 2) Explore how melt strength depends on the specific chain architecture, e.g., the number of branching points per chain; 3) Examine whether the entanglement network with LCB may suffer strain localization upon large deformation; 4) Identify key molecular structural parameters that define/determine the cohesion and dictates nonlinear responses to large deformations; 5) Study the effect of mixing different components of LCBs or LCB and linear chains on the nonlinear dynamics. To achieve these goals, both simple and uniaxial extension will be carried out involving either startup or step strain. In all cases, effective particle-tracking velocimetric (PTV) observations will be indispensable and systematically carried out. In the case of shear, a circular Couette shear cell will be employed with PTV capability. Uniaxial extension will be realized either with the counter-rotating double-cylinder device or Instron where in situ PTV measurements will also be performed. NON-TECHNICAL SUMMARYThis research aims to explore and identify guiding fundamental principles that may find application in more efficient and energy-saving manufacturing of polymeric materials. These principles will ultimately emerge from the present proposed work, aimed to determine how different molecular designs of polymeric materials would affect the processing ability of plastics and rubbers. The outcome of the proposed work should lead to explicit information valuable to the plastic and rubber industries. At the same time, the experimental activities are expected to stimulate theoretical development in the field of polymer physics. More broadly, the PI plans to consolidate the findings from this research into a textbook, which would include all the key results emerging from his contributions to this field. Since the nature of the proposed research is visualization-intensive, complex physical phenomena can receive intuitive interpretations, thus providing attractive educational materials for students in middle and high schools to perceive how science is done. As part of the research activities, an international collaboration has also been initiated with the Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences, aiming to carry out computer simulations complementary to the various proposed experiments.