CAREER: Complex Phase Behavior in Block Copolymer Materials

所有材料的特性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。在一类称为“嵌段共聚物”的材料中自发形成（“自组装”）的纳米尺寸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。到目前为止，对于嵌段共聚物可以获得什么样的纳米结构仍然没有完全的了解，这限制了它们可能被使用的新方法。该计划将揭示基本的分子设计规则，通过实验和理论相结合，控制嵌段共聚物的结构形成。该方法利用合成来系统地操纵聚合物化学，使用被预测为稳定独特结构的概念。X射线测量将提供对自组装如何依赖于成分和加工的深入了解。模拟将合理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促进科学的进步，阐明类型的结构/性能关系，是中央的软材料的实用性。 该提案的推广部分涉及通过针对小学，本科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。一系列的动手结构/性能研讨会将提供7- 12年级的学生介绍聚合物科学使用化学和物理的基本概念。这些示范的影响将通过教师培训得到扩大，教师培训提供了一个不断改进和使用的机制。课程的发展将进一步有利于本科生和研究生谁有兴趣在先进的主题与拟议的research.Technical摘要：嵌段共聚物的效用来自于他们的能力，自组装成有序的介观结构，但传统的相行为的材料与两种类型的嵌段化学是有限的，以少数的经典形态。近年来，在简单的AB两嵌段共聚物熔体中发现了许多复杂的球形填充相，称为Frank-Kasper相。 然而，到目前为止，仍然有一个不完整的理解什么结构是可访问的，为什么他们的发展，以及如何偏向他们的形成。该计划将揭示材料设计原理，这些原理使用合成，物理表征和理论相结合的方法将嵌段共聚物自组装成非经典相。支撑这项研究的中心假设假定，已知促进界面曲率的三个因素将影响复杂的相行为：（1）极端的构象不对称性，其形式为嵌段之间的统计片段长度差异，（2）杂臂星星结构，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（丙交酯）和聚（（甲基）丙烯酸烷基酯）嵌段，可以对所有三个目标进行系统控制。小角度X射线散射将被用来询问这些材料在倒易空间中的结构，并通过密度重建和电子显微镜来探测真实的空间。流变测量将提供洞察有序无序和有序有序的转变。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中自组装和介观包装的基本因素来推进知识。该奖项反映了NSF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.