Anisotropic Self-Assembly of Spherical Nanoparticles in Polymer Nanocomposites

技术总结：PI小组最近发现，接枝有长聚合物链的球形纳米颗粒，当它们与结构相同但比刷子长的“基质”链混合时，会组装成高度各向异性的薄片。样品必须在高于聚合物的玻璃化转变温度的延长时间段内退火，以使这些片材形成和生长。最初的TEM断层扫描结果表明，这些片是几个（2-5）颗粒厚，但它们的横向范围可以大到几十微米。这些尺寸类似于粘土片的尺寸，粘土片已被广泛用于聚合物纳米复合材料中，以实现机械性能、气体渗透性和阻燃性的前所未有的改善。这一提议表明，球形颗粒组装成片状形态的能力应该允许类似的性能改进。在这一点上，决定这种不寻常的组装过程的因素还不清楚。因此，在这里，提出了一个高度集成的理论和实验的努力，可控地实现均匀的颗粒分散（当矩阵链比刷短）和高度各向异性的系统跨越颗粒结构（当刷比矩阵短）的限制之间的形态的目标。具体而言，将重点讨论控制球形颗粒自组装形成的形状的因素，以及它们是平衡的还是动力学产生的。还将涉及所得形态与宏观性能之间的关系，以便获得具有所需性能的纳米复合材料。非技术总结：在潜在应用的背景下，显然创建具有可控各向异性的结构的能力是令人兴奋的，因为先前的工作已经表明，当高度各向异性的物体，例如碳纳米管或粘土片被加入到聚合物中。自发地将纳米颗粒组装成具有可控横向尺寸的“片”的能力可以允许创建具有可调电，机械和传输特性的易于加工的材料。除了一个有趣的物理情况的调查，PT应继续通过各种论坛指导本科生和研究生。他将继续发展REU计划，这些计划将针对代表性不足的少数民族。与Ramakrishnan教授（佛罗里达A M大学，一所历史上的黑人学校）建立的合作关系将被用来招收本科生，目标是留住他们在科学领域的人才。P1还将开发课程，教授研究生一个新领域的基础知识，即应用于凝聚相系统的多尺度建模。P1还在纽约市地区为K-12学生教授科学，目前正在指导一名8年级学生的科学项目。

Technical Summary: The PIs group has recently found that spherical nanoparticles, which are grafted with long polymer chains, assemble into highly anisotropic sheets when they are mixed with "matrix" chains of the same structure but which are longer than the brush. The samples have to be annealed for extended periods of time above the glass transition temperature of the polymer for these sheets to form and grow. Initial TEM tomography results suggest that these sheets are a few (2-5) particles thick, but that their lateral extent can be as large as tens of micrometers. These dimensions are akin to those of clay sheets, which have been extensively used in polymer nanocomposites to achieve unprecedented improvements in mechanical properties, gas permeation and flame retardancy. This proposal conjectures that the ability of spherical particles to assemble into sheet-like morphologies should allow for similar property improvements. At this point the factors which dictate this unusual assembly process are not understood. Thus, here, a highly integrated theoretical and experimental effort is proposed with the goal of controllably achieving morphologies between the limits of uniform particle dispersion (when the matrix chains are shorter than the brush) and highly anisotropic system spanning particle structures (when the brushes are shorter than the matrix). Specifically, the factors controlling the shapes that can be formed by self-assembling spherical particles, and if they are equilibrium or kinetically created will be focused on. The relationship between the resulting morphology and macroscopic properties will also be touched on so that nanocomposites with desired properties can be obtained.Non-Technical Summary: The ability to apparently create structures with controllable anisotropy is exciting in the context of potential applications since previous work has shown that unusual improvements in properties are achieved when highly anisotropic objects, such as carbon nanotubes or clay sheets, are added to polymers. The ability to spontaneously assemble nanoparticles into 'sheets" with, presumably, controllable lateral dimensions could allow for the creation of easily processable materials with tunable electrical, mechanical and transport properties. In addition to the investigation of an interesting physical situation, the Pt shall continue to mentor undergraduate and graduate students through a variety of forums. He will continue to develop REU programs which will target underrepresented minorities. An established collaboration with Prof. Ramakrishnan (Florida A&M University, a historically black school) will be leveraged to recruit undergraduate students with the goal of retaining them in the sciences. The P1 will also develop courses to teach graduate students the fundamentals of a new field, muttiscale modeling as applied to condensed phase systems. The P1 also teaches science to K-12 students in the New York city area, and is currently mentoring an 8th grade student on an science project.