Structure and Dynamics of Asymmetric Block Copolymers

嵌段聚合物是一类将两种或两种以上不同化合物的物理性质结合成单一材料的大分子。在理解与嵌段聚合物相关的分子尺度结构方面的最新进展，已经在许多技术领域带来了创新的新应用，包括电池、心血管支架、用于包装和保健产品的坚韧通用塑料，以及计算机芯片的制造。最近，在最简单的一种被称为“双嵌段共聚物”的化合物中发现了令人惊讶的纳米级分子组织的新状态，这种化合物只包含两个端对端连接的聚合物分子。当设计成不对称组成时，这些二嵌段共聚物形成各种有序结构，模仿金属和合金的行为。本研究项目旨在揭示与这种显著相行为相关的基本分子现象，目的是建立自组装软材料中准晶体等低对称相发展的基本原理。学生和博士后将合成有用数量的模型二嵌段共聚物，并使用一系列实验工具，包括x射线散射、电子显微镜、机械光谱学和光学方法，研究这些材料的结构和动力学。这项研究将同时培养聚合物领域未来的领导者，同时推进知识的基础，使嵌段聚合物扩展应用于无数技术先进的产品，为社会服务。与明尼苏达科学博物馆的合作将吸引公众参与令人兴奋的材料科学与工程领域。技术概述嵌段共聚物在合成聚合物领域处于领先地位，提供了无数的机会来推进我们对软材料的基本理解，同时解决与材料科学和工程相关的各个学科的无数技术应用。二嵌段共聚物是这类自组装材料中最简单的分子结构，其最新进展揭示了不对称分子结构限制下的有序和无序的非凡新概念，从而形成了离散的、名义上的球形颗粒。该项目概述了一个雄心勃勃的实验计划，旨在揭示在二嵌段共聚物熔体中形成四面体紧密排列的Frank-Kasper相和准晶体的基本原理。模型材料将以接近单分散的形式合成，并使用小角度x射线散射和电子显微镜进行结构表征。控制相变动力学的分子传输现象将使用时间分辨技术进行评估，包括小角中子散射、光学方法和动态机械光谱学。该程序将建立控制低对称相形成的原则，作为分子结构、分散性、组成和构象不对称以及纯嵌段共聚物和共混物分子量的函数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYBlock polymers are a class of macromolecules that combine the physical properties of two or more different compounds into a single material. Recent advances in understanding the molecular-scale structure associated with block polymers has led to innovative new applications in numerous areas of technology including batteries, cardiovascular stents, tough versatile plastics for use in packaging and health care products, and manufacturing of computer chips. Surprising new states of nanoscale molecular organization have recently been discovered in the simplest type of such compounds known as "diblock copolymers", which contain just two polymer molecules linked end-to-end. When designed with an asymmetric composition these diblock copolymers form a variety of ordered structures that mimic the behavior of metals and alloys. This research program aims to uncover the fundamental molecular phenomena associated with this remarkable phase behavior, with the goal of establishing the basic principles responsible for the development of low-symmetry phases including quasicrystals in self-assembled soft materials. Students and post docs will synthesize useful quantities of model diblock copolymers and investigate the structure and dynamics of these materials using a host of experimental tools including X-ray scattering, electron microscopy, mechanical spectroscopy, and optical methods. This research will simultaneously train future leaders in the field of polymers while advancing the fundamental base of knowledge enabling expanded application of block polymers to myriad technologically advanced products that serve society. A collaboration with the Science Museum of Minnesota will engage the public in the exciting field of materials science and engineering. TECHNICAL SUMMARYBlock copolymers command a leading position in the field of synthetic polymers, offering innumerable opportunities to advance our fundamental understanding of soft materials while addressing myriad technological applications across various disciplines associated with materials science and engineering. Recent advances with diblock copolymers, the simplest molecular architecture in this category of self-assembling materials, have exposed extraordinary new concepts regarding order and disorder in the limit of asymmetric molecular architectures leading to the formation of discrete, nominally spherical particles. This project outlines an ambitious experimental program designed to uncover the basic principles responsible for the formation of tetrahedrally close-packed Frank-Kasper phases and quasicrystals in diblock copolymer melts. Model materials will be synthesized in nearly monodisperse form and characterized structurally using small-angle X-ray scattering and electron microscopy. The molecular transport phenomena that govern phase transition dynamics will be assessed using time-resolved techniques including small-angle neutron scattering, optical methods and dynamic mechanical spectroscopy. This program will establish the principles that govern the formation of low symmetry phases as a function of molecular architecture, dispersity, compositional and conformational asymmetry, and molecular weight in pure block copolymers and blends.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.