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

研究综述：在粘弹性流动函数与聚合物结构相关的本构方程的开发和评估中，迫切需要各种剪切模式下具有良好特性的聚合物结构中系统变化的流动函数数据。对于线性聚合物，将确定相对分子质量、重量分布、刚性和复杂性对流动函数的影响。此外，对于支化聚合物，将确定星形聚合物的支化数量、长度和均匀性的影响，以及梳状和随机支化的聚合物的支化分布。流动函数将包括粘度，特别是第一和第二法向应力差n1和n2，以及在稳定剪切、振荡、应力增长和松弛以及阶跃应变变形中的派生函数。低柔度Weissenberg流变仪和流变仪将用于锥板和平行板剪切。将研究本构方程的修正，特别是松弛函数的修正。技术影响/实际应用：完整的流动函数数据将为在聚合物生产和加工设备设计中与输运方程一起使用的实际本构方程的制定提供基础。以下是一些应用：挤出物膨胀。挤出物膨胀的控制在塑料管、棒材和塑料容器型材的挤出等操作中至关重要。很少有的n2与n1的比率已被证明是挤出物膨胀的一个主要因素。拟议的研究将产生获取此类数据所需的高剪切率数据和仪器。钢丝涂层。第二，法向应力差和流体动力作用于塑料涂层中的导线中心。利用这些力设计的模具可以减少平均涂层厚度，满足厚度规格，并降低材料成本。根据这一提议开发的仪器将首次使获取所需的高剪切率氮气数据成为可能。必须对食品、聚合物或塑料行业的搅拌机和反应器竖井爬升进行管理。在一个案例中，聚合物爬上竖井，进入大型搅拌机的驱动器，迫使代价高昂的关闭。有了n2与n1之比的知识(目前很少有)，就可以预测杆的爬升，并可以设计混合器来避免这些问题。倒流。在搅拌槽聚合物、生物反应器和搅拌器中，显著的法向应力导致径向向内流向搅拌器轴(而不是径向向外)。流动模式的重大变化大大降低了传质、换热和效率。在了解了N_2与N_1的比率后，可以预测反向流动，并采取设计措施来改善性能。

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.