Second Newtonian region of polymer solutions

聚合物溶液的第二牛顿区域

• 批准号: 290025643
• 负责人: Professor Dr. Andreas Wierschem
• 金额: --
• 依托单位: Lehrstuhl für Strömungsmechanik (LSTM)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/290025643?language=en
• 关键词: Second; Newtonian; region; polymer; solutions

Polymer solutions are a class of fundamental rheological systems with countless applications. Their viscosity typically depends strongly on the shear load: At low shear rates, in the 1st Newtonian branch, the polymer solutions have a constant viscosity. Beyond this branch, the viscosity diminishes considerably. Finally, at very high shear rates another regime of constant viscosity, the 2nd Newtonian branch is expected. Apart from shear rate, the viscosity depends substantially on the type of polymer and its structure, the molecular weight and its distribution, the polymer concentration, and on the solvent. In the 1st Newtonian branch, different regimes of polymer solutions can be distinguished depending particularly on concentration and on molecular weight. While the 1st Newtonian branch and the onset of shear thinning are well studied, this is not the case for the 2nd Newtonian branch. Here, detailed knowledge about viscosity, normal-stress differences and the orientation of the polymers, their dependencies on the above-mentioned parameters as well as studies about the onset of the 2nd Newtonian branch are lacking. Proper knowledge about this branch, however, is not only necessary for a fundamental understanding of polymer solutions but is also needed in a number of industrial applications. Essential reason for the lack of knowledge about the 2nd Newtonian branch is the deficiency of adequate measuring technique: The shear-rate range is typically 1-2 decimal orders beyond the parameter range covered by commercial rheometers. Besides, very low viscosities need to be detected. We have improved the geometrical precision of rotational rheometers by about a factor of 30 to 100. This permits measurements at considerably narrower gaps that enable reaching the necessary high shear rates and precision. Furthermore, to the best of the authors knowledge, the improved rheometer is the only one that allows for detecting normal forces in polymer solutions and for carrying out rheo-optical studies at shear rates up to 105 s-1. It is aimed for further enhancing the precision within the project. Central aim of the project is to characterize the 2nd Newtonian branch of well-defined as well as industrially relevant polymer solutions. Simultaneously with the viscosity measurements, shear-induced normal forces due to the solution viscoelasticity and the orientation of the polymers are to be detected. The latter is to study whether the microstructure changes in the 2nd Newtonian branch. The main issue is to clarify if there are different regimes as a function of polymer concentration in the 2nd Newtonian branch similar to those in the 1st Newtonian branch. Furthermore, the impact of molecular weight, changes in polymer structure and solvent should be elucidated. To avoid shear-induced degradation, the study is planned to be carried out with semi-flexible polymers.

聚合物溶液是一类具有无数应用的基本流变系统。它们的粘度通常很大程度上取决于剪切载荷：在低剪切速率下，在第一牛顿分支中，聚合物溶液具有恒定的粘度。超过这个分支，粘度大大降低。最后，在非常高的剪切速率下，另一种恒定粘度的制度，第二牛顿分支是预期的。除了剪切速率外，粘度在很大程度上取决于聚合物的类型及其结构、分子量及其分布、聚合物浓度以及溶剂。在第一牛顿分支中，聚合物溶液的不同状态可以根据浓度和分子量来区分。虽然第一牛顿分支和剪切变薄的开始得到了很好的研究，但第二牛顿分支的情况并非如此。在这里，缺乏关于聚合物的粘度、法向应力差和取向的详细知识，以及它们对上述参数的依赖关系，以及关于第二牛顿分支开始的研究。然而，对这一分支的适当了解不仅是对聚合物溶液的基本理解所必需的，而且在许多工业应用中也是必需的。缺乏牛顿第二分支知识的根本原因是缺乏适当的测量技术：剪切速率范围通常比商业流变仪所涵盖的参数范围超出1-2个十进制数量级。此外，需要检测非常低的粘度。我们已经将旋转流变仪的几何精度提高了大约30到100倍。这允许在相当窄的间隙进行测量，从而达到所需的高剪切速率和精度。此外，据作者所知，改进的流变仪是唯一一种允许检测聚合物溶液中的法向力和在高达105 s-1的剪切速率下进行流变光学研究的流变仪。它旨在进一步提高项目内的精度。该项目的中心目标是描述定义良好的第二牛顿分支以及工业相关的聚合物解决方案。在进行粘度测量的同时，还需要检测由溶液粘弹性和聚合物取向引起的剪切诱导法向力。后者是研究在第二牛顿分支中微观结构是否发生变化。主要问题是澄清是否有不同的制度作为聚合物浓度的函数在第二牛顿分支类似于那些在第一牛顿分支。此外，还应阐明分子量、聚合物结构变化和溶剂的影响。为了避免剪切引起的降解，研究计划用半柔性聚合物进行。