Criteria for Flow-Induced Crystalization of Polymers: The Effect of Strong Shear and Extensional Flows

CBET- 0651888H.H.温特，马萨诸塞州阿默斯特大学该计划的目标是获得更深入的了解流动诱导结晶的聚合物。这些进展包括剪切下的流变光学实验，单轴拉伸下的流变光学实验，和建模与几个最先进的流变本构方程预测流动诱导的分子拉伸和取向。最近在NSF MRI资助下获得的独特光学微流变仪和新型细丝拉伸拉伸流变仪能够同时测量均匀剪切和拉伸流动中应力和材料结构随时间和累积应变的变化。同时观察光散射，显微镜，荧光，和双折射从样品，使之有可能获得时间相关的聚合物熔体的结构信息。这些新仪器设计用于在聚合物加工中经常遇到的大剪切和拉伸速率下对非常小的样品进行研究。他们将允许聚合物结晶勘探，促进应力和晶体结构生长的第一次同时测量响应均匀剪切流，均匀单轴拉伸流，精确控制的顺序均匀剪切和单轴拉伸流。模拟应变对聚合物构象和拉伸的影响将使用新开发的网络基础设施（计算机辅助）方法，这些方法通过将流变学实验与非线性粘弹性的分子理论相结合而变得可用。先进的分子动力学理论将预测各种分子拓扑结构（线性，短链支化，星形，pom-pom）和各种分子量分布的聚合物熔体中的流动诱导分子拉伸和取向。模型预测可能能够在大应力和应变下对结晶动力学进行分类，并将观察结果与分子结构联系起来。智力优势：拟议的流动诱导聚合物结晶研究代表了新开发的实验技术和设施与最先进的本构模型和理论之间的强大协同作用，以探索凝胶点附近流体的应力和结构。本论文将针对聚合物熔体的静态结晶和流动诱导结晶的几个关键领域进行一系列精心设计的实验。强均匀剪切和拉伸流将被用来探索剪切速率，拉伸速率，应变，应变能，和支化的晶体成核和聚合物熔体的生长速率的作用。更广泛的影响：拟议的研究可以对许多商业应用产生重大影响，从促进具有特定应用特性的材料的设计到减少制造聚合物基部件的时间和成本。这些进展不仅需要详细了解剪切和拉伸流动对结晶过程的作用，而且需要开发能够精确控制结晶动力学的处理方案和设备。此外，拟议的工作将加强教育，包括研究生和本科生的研究项目。该学院成功的少数民族工程项目将有助于使代表性不足的群体参与拟议的研究。网络基础设施（CI）的学生将直接访问几个世界上最先进的聚合物动力学理论。实验技术和CI的结合构成了一个强大的教学工具，与东北联盟研究生教育合作伙伴（NEAGE）机构的教师分享。Estevez博士（美国）（波多黎各）将合作开发专门设计用于材料科学课程实施的CI模块。在NEAGE的帮助下，他将访问马萨诸塞大学阿默斯特分校，以了解更多关于CI平台和拟议实验的信息，然后将其融入他的课程。像CI这样的活动建立了与科学和技术界的桥梁，使各种背景的学生能够在很高的水平上从事科学和技术。

CBET- 0651888H.H. Winter, University of Massachusetts AmherstThe program goal is to gain a deeper understanding of flow-induced crystallization of polymers. These advances include rheo-optical experiments under shear, rheo-optical experiments under uniaxial extension, and modeling with several of the most advanced rheological constitutive equations for predicting flow-induced molecular stretch and orientation. A unique optical micro-rheometer and a novel filament stretching extensional rheometer, recently obtained under an NSF MRI grant, are capable of simultaneously measuring the evolution of stress and material structure as a function of time and accumulated strain in homogeneous shear and extensional flows. Simultaneous observation of light scattering, microscopy, fluorescence, and birefringence from the sample make it possible to obtain time-correlated structural information of the polymer melts. These new instruments were designed for studies on very small samples at the large shear and extension rates often encountered in polymer processing. They will allow polymer crystallization exploration by facilitating the first simultaneous measurements of stress and crystal structure growth in response to homogenous shear flows, homogeneous uniaxial extensional flows, and precisely controlled sequential homogeneous shear and uniaxial extensional flows. Modeling the effect of strain on the polymer conformation and stretch will use newly developed cyber infrastructure (computer aided) methods that have become available by combining rheological experiments with molecular theory for non-linear viscoelasticity. Advanced molecular dynamics theories will predict the flow-induced molecular stretch and orientation in polymer melts of various molecular topology (linear, short-chain branched, stars, pom-pom) and various molecular weight distributions. Model predictions might be able to classify crystallization dynamics at large stresses and strains and connect the observations back to the molecular architecture. Intellectual Merit: The proposed flow-induced polymer crystallization research represents a strong synergy between newly developed experimental techniques and facilities and state-of-the-art constitutive models and theories to explore the stress and structure of fluids near the gel point. A series of well-designed experiments will be performed into several key areas of quiescent crystallization and flow-induced crystallization of polymer melts. Strong homogenous shear and extensional flows will be used to explore the role of shear rate, extension rate, strain, strain energy, and branching on the rate of crystal nucleation and growth of polymer melts. Broader Impacts: The proposed research can have significant impact on a host of commercial applications from facilitating the design of materials with application specific properties to reducing the time and cost of manufacturing polymer based parts. These advances require not only a detailed understanding of the role of shear and extensional flows on the crystallization process, but the development of processing protocols and equipment which can precisely control the dynamics of crystallization. In addition, the proposed work will enhance education, by including both graduate and undergraduate students in the research project. The college's successful Minority Engineering Program will help involve underrepresented groups in the proposed research. Cyberinfrastructure (CI) students will directly access several of the world's most advanced theories of polymer dynamics. The combination of experimental techniques and the CI constitutes a powerful teaching tool to share with faculty of Northeast Alliance for Graduate Education Partner (NEAGE) institutions. Dr. Estevez (U. of Puerto Rico) will collaborate in the development of CI modules specifically designed for implementation in his materials science curriculum. With the aid of the NEAGE, he will visit UMass Amherst to learn more about the CI platform and the proposed experiments and will then integrate them into his courses. Activities like CI build bridges to the science and technology community making it possible for students of all backgrounds to engage in science and technology at a very high level.