CAREER: Complex Phase Behavior in Block Copolymer Materials

非技术概要：所有材料的性质都取决于它们在不同长度尺度上的结构，从原子的微观排列到加工过程中形成的宏观形状。在一种被称为“嵌段共聚物”的材料中自发形成（“自组装”）的纳米级结构被广泛用于制造合成橡胶、粘合剂和下一代计算机芯片等应用。迄今为止，人们对嵌段共聚物可获得的纳米结构仍有不完全的了解，这限制了它们可能使用的新方法。该程序将通过实验和理论的结合揭示控制嵌段共聚物结构形成的基本分子设计规则。该方法利用合成来系统地操纵聚合物化学，使用预测稳定独特结构的概念。x射线测量将提供洞察如何自组装取决于成分和加工。模拟将解释为什么某些结构比其他结构更稳定，并为精细的分子设计提供信息。在这项研究中发现的基础知识将通过阐明软材料的核心用途的结构/性质关系的类型来促进科学的进步。该提案的延伸部分包括通过针对小学，本科生和研究生的计划，扩大对聚合物科学的兴趣，特别是在代表性不足的人口中。一系列动手结构/性质研讨会将为7-12年级的学生提供使用化学和物理基本概念的聚合物科学介绍。这些示范的影响将通过提供持续改进和使用机制的教师培训而扩大。课程开发将进一步有利于本科生和研究生谁感兴趣的高级主题与拟议的研究一致。技术概述：嵌段共聚物的应用源于其自组装成有序介观结构的能力，但具有两种类型嵌段化学的材料的传统相行为仅限于少数经典形态。最近，在简单的AB二嵌段共聚物熔体中发现了许多称为Frank-Kasper相的复杂球体填料。然而，到目前为止，对于哪些结构是可接近的，它们为什么形成，以及如何偏爱它们的形成，人们仍然没有完全理解。本课程将通过合成、物理表征和理论的结合，揭示控制嵌段共聚物自组装成非经典相的材料设计原则。支撑本研究的中心假设假设，已知的促进界面曲率的三个因素将影响复杂相行为：(1)以统计片段长度差异形式出现的极端构象不对称，(2)mitoarm星结构，以及(3)分子分散性。这些主题将通过一个统一的材料平台进行研究，该平台包括聚（丙烯酰胺）和聚（烷基（甲基）丙烯酸酯）块，能够系统地控制所有三个目标。小角度x射线散射将用于询问这些材料在互反空间中的结构，并通过密度重建和电子显微镜来探测真实空间。流变测量将提供对有序-无序和有序-有序过渡的洞察。自洽场理论模拟将被用来合理化这些观察和指导迭代分子设计。计划中的研究将通过揭示控制软材料自组装和介观包装的基本因素来推进知识。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 SUMMARY:The properties of all materials depend on their structure across various length scales, from the microscopic arrangement of atoms to macroscopic shapes fashioned during processing. Nanometer-sized structures that spontaneously form ("self-assemble") in a class of materials known as "block copolymers" are widely used to create synthetic rubbers, adhesives, and next-generation computer chips among other applications. To date, there remains an incomplete understanding of what nanostructures are accessible with block copolymers, which limits new ways that they might be used. This program will uncover the fundamental molecular design rules that control structure formation in block copolymers through a combination of experiments and theory. The approach leverages synthesis to systematically manipulate polymer chemistry using concepts that are predicted to stabilize unique structures. X-ray measurements will provide insight into how self-assembly depends on composition and processing. Simulations will rationalize why certain structures are stable over others and inform refined molecular design. Fundamental knowledge uncovered in this research will promote the progress of science by elucidating the types of structure/property relationships that are central to the utility of soft materials. The outreach portion of this proposal involves broadening interest in polymer science, particularly among underrepresented demographics, via a plan targeting grade school, undergraduate, and graduate students. A series of hands-on structure/property workshops will provide 7-12th grade students with an introduction to polymer science using basic concepts from chemistry and physics. The impact of these demos will be amplified through teacher training that provides a mechanism for continual improvement and use. Curriculum development will further benefit undergraduate and graduate students who are interested in advanced topics aligned with the proposed research.TECHNICAL SUMMARY:The utility of block copolymers derives from their ability to self-assemble into well-ordered mesostructures, but the traditional phase behavior of materials with two types of block chemistries is limited to a handful of classical morphologies. Recently, a number of complex sphere packings known as Frank-Kasper phases have been discovered in simple AB diblock copolymer melts. However, to date there remains an incomplete understanding of what structures are accessible, why they develop, and how to bias their formation. This program will unravel the material design principles that govern the self-assembly of block copolymers into non-classical phases using a combination of synthesis, physical characterization, and theory. The central hypothesis underpinning this research posits that three factors known to promote interfacial curvature will influence complex phase behavior: (1) extreme conformational asymmetry in the form of statistical segment length differences between blocks, (2) the miktoarm star architecture, and (3) molecular dispersity. These topics will be investigated with a unified materials platform comprising poly(lactide) and poly(alkyl (meth)acrylate) blocks that enables systematic control over all three objectives. Small-angle X-ray scattering will be used to interrogate the structure of these materials in reciprocal space, augmented by density reconstructions and electron microscopy to probe real space. Rheological measurements will provide insight into order-disorder and order-order transitions. Self-consistent field theoretic simulations will be leveraged to rationalize these observations and guide iterative molecular design. The planned research will advance knowledge by revealing fundamental factors that control self-assembly and mesoscopic packing in soft materials.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.