The Effects of Molecular Structure on Polymer Viscoelastic Flow Functions in Steady and Time Dependent Simple Shearing Flow

研究总结：对于聚合物结构的粘弹性流动函数的本构方程的建立和评估，迫切需要表征良好的聚合物结构在各种剪切模式下的系统变化的流动函数数据。对于线性聚合物，分子量、重量分布、刚度和复杂性对流动函数的影响将被确定。此外，对于支链聚合物，将确定星形聚合物的支链数、长度和均匀性以及梳状和随机支链聚合物的支链分布的影响。流动函数将包括粘度，特别是第一和第二正应力差，N1和N2，以及稳定剪切，振荡，应力增长和松弛以及阶跃应变变形的衍生函数。低柔度Weissenberg和Rheometries流变仪将用于锥形板和平行板剪切。本构方程的修正，特别是松弛函数的修正，将被研究。技术影响/实际应用：完整的流动函数数据将为制定现实的本构方程提供基础，用于设计聚合物生产和加工设备中的输运方程。一些应用如下：挤出膨胀。在塑料管材、棒材和塑料容器的挤压过程中，对挤出物膨胀的控制是至关重要的。很少可用的N2与N1的比例已被证明是挤出物膨胀的主要因素。拟议的研究将产生所需的高剪切率数据和仪器来获取这些数据。漆包线漆膜。第二，法向应力差和流体动力作用于钢丝在塑料涂层中的中心。利用这些力设计的模具可以降低平均涂层厚度，满足厚度规格，并降低材料成本。该方案开发的仪器将首次获得所需的高剪切速率N2数据。在食品和聚合物或塑料工业中，搅拌器和反应器轴上的爬井必须加以管理。在一个案例中，聚合物爬上了轴，进入了一个大型搅拌器的驱动器，导致了代价高昂的停机。通过了解N2与N1的比例（目前很少有），可以预测抽油杆的爬升情况，并设计混合器来避免这些问题。反向流动。在搅拌槽聚合物和生物反应器和混合器中，显著的正应力导致径向向内流向混合器轴（相对于径向向外）。流动型态的重大变化大大降低了传质、传热和效率。了解了N2与N1的比例，就可以预测逆流，并采取设计措施来提高性能。

Research Summary: Flow function data for systematic variations in well-characterized polymer structures for a variety of shearing modes are critically needed for the development and evaluation of constitutive equations relating viscoelastic flow functions to polymer structure. The effect on the flow functions of molecular weight, weight distribution, stiffness, and complexity will be determined for linear polymers. Additionally, for branched polymers, the effects of branch number, length, and uniformity for star polymers, and branch distribution for comb and randomly branched polymers will be determined. The flow functions will include the viscosity, and especially the first and second normal stress differences, N1 and N2, and derived functions in steady shearing, oscillatory, stress growth and relaxation, and step strain deformations. Low compliance Weissenberg and Rheometries rheometers will be used in cone-plate and parallel plate shearing. Modification of constitutive equations, especially relaxation functions, will be studied. Technical Impact/Practical Applications: The complete flow function data will provide a basis for the formulation of realistic constitutive equations for use with the transport equations in the design of polymer production and processing equipment. Some applications follow: Extrudate Swell. The control of extrudate swell is critically important in such operations as the extrusion of plastic pipe, rods, and plastic vessel parisons. The rarely available ratio of N2 to N1 has been shown to be a major factor in extrudate swell. The proposed research will generate the required high shear-rate data and instrumentation to acquire such data. Wire Coating. Second normal stress difference and fluid dynamic forces act to center the wire in a coating of plastic. Dies designed to utilize these forces could reduce the average coating thickness, meet thickness specifications, and reduce material costs. The instrumentation developed by this proposal will make possible for the first time the acquirement of the required high shear-rate N2 data. Shaft Climbing on the shafts of mixers and reactors in the food and polymers or plastics industries must be managed. In one case, polymers climbed up the shaft and into the drive of a large mixer and forced a costly shutdown. With a knowledge of the ratio of N2 to N1 (currently rarely available), rod climbing can be predicted and mixers can be designed to avert the problems. Reverse Flow. In stirred tank polymer and biological reactors and mixers, significant normal stresses cause radially inward flow towards the mixer shafts (vs. radially outward). Mass and heat transfer and efficiency are importantly reduced by major changes in flow patterns. With a knowlege of the ratio of N2 to N1, reverse flow can be predicted and design measures taken to improve performance.