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

提案标题：纳米夹杂能否有效降低聚合物熔体的粘度和模数？提案编号：CTS-0400840首席研究员：Michael E.Mackay研究所：密歇根州立大学在这个项目中，正在研究悬浮液或浆料的流动和物理性质。然而，颗粒比分散在其中的流体分子小，这就产生了不寻常的效果。我们已经发现，尺寸为5-10 nm的纳米颗粒悬浮在分子尺寸为15-40 nm的聚合物液体中，产生的液体的粘度低于整齐的聚合物液体本身。降低粘度与爱因斯坦百年前关于布朗粒子增加液体粘度的预测不符。事实上，所有的观察结果都表明，颗粒悬浮液中总是存在粘度增加的现象。最近在《自然材料》杂志上发表了一篇关于这一效应的文章。由于颗粒如此之小，人们认为它们会在局部尺度上影响聚合物液体的动力学。纳米粒子明显增加了聚合物液体中的自由体积，并对聚合物分子进行了限制，从而产生粘度下降。此外，现代量化纠缠的方法表明，纠缠密度没有变化。这项工作的目的是进一步阐明这一现象，解决这一困境。包括在初步结果中的一项最新发现是，化学上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，只要其颗粒比聚合物小。聚乙烯。聚苯乙烯体系是一种模型相分离体系，研究发现，将某一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，它代表了拟议研究的一个方面。这可能会创造出一类新的分子合金。进一步的研究将以富勒烯为模型体系，其尺寸比现有的纳米颗粒小得多，以及单壁碳纳米管作为模型体系，以引入新的颗粒几何形状。这些体系将被用来推广降粘效果。我们将在拟议的工作中使用各种技术来测量纳米颗粒的分散性以及悬浮液的状态。链状分子。这些技术包括：流变特性、热分析、机械测试、电子光学评估和小角中子散射。所有这些仪器都存在于团队中，或在校园内，或在阿贡国家实验室。研究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，就像我们在执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，代表不足的群体的参与将扩大他们的学习经验。这些成果的传播将通过科学文献和会议以及本科生和研究生水平的讲座来介绍。首席研究人员在他教授的入门(二年级)课程中每学期留出一堂课，向学生介绍他的研究。这堂课很受欢迎，向学生介绍了研究过程和研究结果。这项拟议的研究是独一无二的，与当代的观察结果不符。在研究讲座中包括这一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。许多代表不足的学生参加了这次讲座，在讲座结束后的几个月里，他们表现出了对研究的兴趣，并希望与首席调查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.