Steric Frustration at the Nanoscale: Self-Assembly, Chirality, and Fluctuations

非技术性摘要包装奇怪形状的三维物体会导致空间挫折，这意味着很难填充空间。 然而，如果对象是分子，热搅动会对所有的堆积可能性进行采样，要么发现意想不到的新排列，要么保持无序。 最近发现的一个例子是螺旋螺旋相，在这种液体中，香蕉状的分子通过排列成分子尺度的螺旋结构来填充空间。 在这个项目中，将设计和合成弯曲分子，并研究其相行为，目的是探索几何和统计原理，这些原理决定了材料中如何容纳这种空间挫折。 由此产生的设计标准将有广泛的应用，在新材料的基础上控制和使用的空间挫折的发展。 该项目将为初级科学家（本科生，研究生和博士后研究人员）提供机会，参与软材料科学这一令人兴奋的领域的广泛跨学科研究。 技术摘要棒状分子形成双相液晶相，三维流体，其中棒状物的空间堆积在热平衡中诱导长程取向有序。 但是，引入一个简单的化学变化，使棒的形状弯曲，产生一个奇特的新（螺旋螺旋）相，其中分子自发地组织成不同分子取向和纳米级周期的手性螺旋晶格。 该项目的假设是，这些独特的新结构是空间挫折的结果：弯曲的分子形状创造了难以填充的空间口袋，从而吸引了波动最强烈的分子子成分。 这一新制定的组织原则将在一个基础广泛的，协调的程序的分子设计，化学合成，物理表征，和计算机模拟的螺旋双相探索。 特别是，共振软X射线散射将用于表征其纳米级取向结构，并将扩展到探测分子取向波动在纳米级。 所学到的知识将应用于各种软物质系统，包括液晶、聚合物和纳米纤维，旨在创造广泛有用、强大的手段来探测和理解纳米级分子取向动力学。螺旋状手性相的强的集体纳米级手性使其在手性客体分子的对映体分离中的应用以及作为不对称合成的模板介质具有吸引力。这些应用的螺旋形的双相将被探讨。

NONTECHNICAL ABSTRACTThe packing of odd-shaped three dimensional objects can lead to steric frustration, meaning that it's hard to fill space. If the objects are molecules, however, thermal agitation samples all of the packing possibilities, either finding unexpected new arrangements or remaining disorganized. A recently discovered example of this is the heliconical nematic phase, a liquid in which banana-shaped molecules fill space by arranging themselves into molecular-scale helical structures. In this project bent molecules will be designed and synthesized and their phase behavior studied with the goal of exploring the geometrical and statistical principles that govern how such steric frustration is accommodated in materials. The resulting design criteria would have wide ranging applications in the development of new materials based on the control and use of steric frustration. This project will provide its junior scientists (undergraduate student, graduate student, and postdoctoral researchers) with opportunities to participate in broadly interdisciplinary research in an exciting area of soft materials science. TECHNICAL ABSTRACTRod-shaped molecules form nematic liquid crystal phases, three dimensional fluids in which steric packing of rods induces long-range orientational order in thermal equilibrium. But introducing a simple chemical change to make the rods bent in shape produces an exotic new (heliconical nematic) phase in which the molecules spontaneously organize into chiral helical lattices of varying molecular orientation and nanoscale periodicity. The project hypothesis is that these distinctive new structures are a result of steric frustration: the bent molecular shape creates pockets of space which are difficult to fill, thereby attracting the most strongly fluctuating molecular sub-components. This newly formulated organizing principle will be explored in a broad-based, coordinated program of molecular design, chemical synthesis, physical characterization, and computer simulation of heliconical nematic phases. In particular, resonant soft x-ray scattering will be used to characterize their nanoscale orientational structure, and will be extended to probe molecular orientational fluctuations at the nanoscale. What is learned will be applied to a variety of soft matter systems, including liquid crystals, polymers and nanofabrications, with the intention of creating broadly useful, powerful means of probing and understanding nanoscale molecular orientational dynamics. The strong collective nanoscale chirality of the heliconical nematic phase makes it attractive for application in separation of enantiomers of chiral guest molecules, and as a templating medium for asymmetric synthesis. These applications of the heliconical nematic phase will be explored.