Can Nanoscale Inclusions Effectively Reduce the Viscosity and Modulus of Polymer Melts?

提案题目：纳米级包裹体能否有效降低聚合物熔体的粘度和模量？项目编号：ccs -0400840首席研究员：Michael E. MackayInstitution：密歇根州立大学在这个项目中，悬浮液或泥浆的流动和物理性质正在被研究。然而，这些颗粒比分散在其中的流体分子要小，这就产生了不同寻常的效果。我们发现，粒径为5-10纳米的纳米颗粒悬浮在分子量为15-40纳米的聚合物液体中，产生的液体粘度低于纯聚合物液体本身。粘度的降低与爱因斯坦一个世纪前关于布朗粒子增加液体粘度的预言是不一致的。的确，所有的观察都表明，在颗粒悬浮液中粘度的增加总是存在的。最近一篇关于这种效应的文章发表在《自然材料》杂志上。由于颗粒如此之小，人们相信它们会在局部范围内影响聚合物液体的动力学。纳米颗粒明显地增加了聚合物液体的自由体积，并限制了聚合物分子，使粘度降低。此外，当代量化纠缠的方法表明纠缠密度没有变化。本文的目的是进一步阐明这一现象并解决这一困境。初步结果中包含了最近的一项发现，即化学性质非常不同的纳米颗粒（聚乙烯）。聚合物（聚苯乙烯）体系可以分子分散，只要颗粒比聚合物小。聚乙烯。聚苯乙烯体系是一种典型的相分离体系，研究发现将一种组分的分子拓扑结构改变为颗粒状构象会影响其在聚合物液体中的溶解度和稳定性。这是一个独特的结果，目前还没有完全理解，代表了拟议研究的一个方面。这可能创造出一类新的分子合金。进一步的研究将以富勒烯和单壁碳纳米管作为模型系统进行，前者的尺寸比现有的纳米颗粒小得多，后者将引入新的颗粒几何结构。这些系统将用于推广降粘效果。我们将在提议的工作中使用各种技术来测量纳米粒子的分散以及悬浮流体的状态。连锁的分子。这些技术包括：流变学表征、热分析、力学测试、电子光学评价和小角中子散射。所有这些仪器都存在于小组中，在校园或在阿贡国家实验室可用。研究小组的研究生和本科生将接触到这些结果，在某些情况下将收集结果，就像我们在进行中子散射时所做的那样。研究小组中有三名女性和三名男性，通过团队合作参与一个代表性不足的群体将拓宽他们的学习经验。这些成果将通过科学文献和会议以及通过本科和研究生水平的讲座进行传播。首席研究员每学期在他教授的导论（二年级）课程中留出一节课向学生介绍他的研究。这个讲座很受欢迎，并向学生介绍了研究过程和研究结果。提出的研究是独特的，与当代观察结果不一致。在研究讲座中包含这个主题将展示科学和工程是如何不断发展而不是停滞不前的。许多未被充分代表的学生参加了这次讲座，并在讲座结束后立即，以及之后的几个月里，表现出对研究的兴趣，并希望与首席研究员或其他教授一起进行研究。

Proposal Title: Can Nanoscale Inclusions Effectively Reduce the Viscosity and Modulus of Polymer Melts?Proposal Number: CTS-0400840Principal Investigator: Michael E. MackayInstitution: Michigan State UniversityIn this project, the flow and physical properties of a suspension or slurry is being investigated. However, the particles are smaller than the fluids molecules in which they are dispersed and this produces unusual effects. We have found that nanoparticles with a size of order 5-10 nm suspended in a polymeric liquid with molecules of size 15-40 nm produce a liquid that has a viscosity lower than the neat polymeric liquid itself. A viscosity reduction is at odds with Einsteins century old prediction that Brownian particles increase the viscosity of liquids. Indeed all observations suggest that a viscosity increase is always present in particulate suspensions. A recent publication on this effect is in press in the journal Nature Materials. Since the particles are so small it is believed they influence the dynamics of the polymeric liquid on a local scale. The nanoparticles apparently increase the free volume in the polymeric liquid as well as confine the polymer molecules to produce the viscosity decrease. Further, contemporary methods to quantify entanglements suggest no change in the entanglement density. It is the purpose of this work to further elucidate the phenomenon and resolve this quandary. A recent discovery, included in the preliminary results, is that very chemically different nanoparticle (polyethylene). polymer (polystyrene) systems can be molecularly dispersed as long as the particle is smaller than the polymer. The polyethylene. polystyrene system is a model phase separating system and it has been discovered that changing the molecular topology of one component into a particle-like conformation affects its solubility and stability in a polymeric liquid. This is a unique result, not fully understood at present and represents one aspect of the proposed research. This could create a new class of molecular alloys. Further research will be conducted with fullerenes, as a model system whose size is much smaller than available nanoparticles, and single wall carbon nanotubes, as a model system to introduce a new particulate geometry. These systems will be utilized to generalize the viscosity reduction effect. We will use a variety of techniques in the proposed work to measure the dispersion of the nanoparticles as well the state of the suspending fluids. chain-like molecules. These techniques include: rheological characterization, thermal analysis, mechanical testing, electron optics evaluation and small angle neutron scattering. All this instrumentation exists in the group, is on campus or is available at Argonne National Laboratory. Graduate and undergraduate students in the research group will be exposed to these results and in some cases will gather results together as we have done when performing neutron scattering. There are three females and three males in the research group and through teamwork participation of an underrepresented group will broaden their learning experience. Dissemination of these results will be presented through the scientific literature and conferences as well as through undergraduate and graduate level lectures. The principal investigator sets aside one lecture every semester in the introductory (sophomore) course he teaches to introduce his research to the students. This lecture is well received and gives students an introduction to the research process as well as the results of research. The proposed research is unique and is at odds to contemporary observations. Inclusion of this topic in the research lecture will demonstrate how science and engineering is continuously evolving and not stagnant. Many underrepresented students attend this lecture and immediately after, as well as for many months thereafter, they show interest in research and wish to undertake research with the principal investigator or other professors.