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

聚合物流动诱导结晶的标准：强剪切和拉伸流动的影响

• 批准号: 0651888
• 负责人: Triantafillos Mountziaris
• 金额: --
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-15 至 2011-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0651888&HistoricalAwards=false
• 关键词: Criteria; Flow; Induced; Crystalization; Polymers

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.

CBET- 0651888H.H.温特，马萨诸塞大学阿默斯特分校该项目的目标是更深入地了解聚合物的流动诱导结晶。这些进步包括剪切下的流变光学实验、单轴延伸下的流变光学实验，以及使用几个最先进的流变本构方程进行建模，用于预测流动引起的分子拉伸和取向。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中应力和材料结构随时间和累积应变的变化。同时观察样品的光散射、显微镜、荧光和双折射，可以获得聚合物熔体的时间相关结构信息。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研究非常小的样品。它们将通过促进首次同时测量响应均匀剪切流、均匀单轴拉伸流和精确控制的顺序均匀剪切和单轴拉伸流的应力和晶体结构生长来进行聚合物结晶探索。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实验与非线性粘弹性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（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流动引起的分子拉伸和取向。模型预测可能能够对大应力和应变下的结晶动力学进行分类，并将观察结果与分子结构联系起来。智力优点：所提出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。一系列精心设计的实验将在聚合物熔体静态结晶和流动诱导结晶的几个关键领域进行。将使用强均匀剪切和拉伸流来探索剪切速率、拉伸速率、应变、应变能和支化对聚合物熔体的晶体成核和生长速率的作用。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属性的材料设计到减少制造基于聚合物的零件的时间和成本。这些进步不仅需要详细了解剪切流和拉伸流对结晶过程的作用，还需要开发能够精确控制结晶动力学的加工方案和设备。此外，拟议的工作将通过让研究生和本科生参与研究项目来加强教育。该学院成功的少数族裔工程计划将有助于让代表性不足的群体参与拟议的研究。网络基础设施（CI）学生将直接接触世界上最先进的聚合物动力学理论。实验技术与 CI 的结合构成了一个强大的教学工具，可以与东北研究生教育联盟合作伙伴 (NEAGE) 机构的教师共享。 Estevez 博士（波多黎各大学）将合作开发专为在其材料科学课程中实施而设计的 CI 模块。在 NEAGE 的帮助下，他将访问麻省大学阿默斯特分校，了解有关 CI 平台和拟议实验的更多信息，然后将其整合到他的课程中。像 CI 这样的活动架起了通往科学技术界的桥梁，使各种背景的学生都有可能参与高水平的科学技术。