CAREER: Stimuli-Responsive Self-Assembly of Supramolecular Block Copolymers: Hierarchical Structures and Kinetic Pathways

该奖项支持与教育相结合的理论和计算研究，以调查复杂聚合物如何组装，并有助于开发复杂聚合物材料的设计原则。自组装是分子或原子由于组成部分之间的相互作用而组织成有序结构的过程。这个过程发生在分子或单体组装成分子构建块的过程中，这些分子构建块可以自己按顺序组装，形成被称为聚合物的长链状分子。聚合物几乎无处不在——它们构成了植物、塑料、我们吃的食物，甚至我们自己的身体。通过对单体序列和分子结构的越来越精确的控制，聚合物已经从大规模的商品塑料转变为精确的自组装构建块，可以通过预编程组织成具有更复杂结构的材料。很可能进一步扩大聚合物的范围，在单体之间可能的键合的广谱上，新的自组装工艺可能会出现，这将带来传统共价聚合物无法实现的功能。该项目的重点是研究所谓的超分子嵌段共聚物的自组装过程，这是一类“杂化键”聚合物，由共价聚合物的结构单元通过温度响应可逆键连接成明确的结构。PI旨在了解分子水平上键的可逆性与自组装过程中的温度响应特征之间的基本联系，无论是在平衡过程还是在动态过程中。通过计算机模拟和量化可逆键对自组装过程的影响，该项目旨在确定制造材料和材料设计的新途径。目标是制定规则，将可预测的结构和动力学性质纳入聚合物材料。作为该项目教育部分的一部分，该项目旨在通过为高年级本科生和研究生开发一门社区参与学习课程“聚合物工程应用中尺度模拟入门”，将课堂学习、研究项目和社区服务结合起来。这项工作将与当地水设施合作，测试/开发基于可回收聚合物的废水处理方法。“社区参与学习”课程有三个目标：(1)提高社区对培训新一代劳动力的认识；(2)培养和促进大学和斯塔克维尔市之间持久的伙伴关系；(3)开发对当地社区潜在有益的技术。该奖项支持与教育相结合的理论和计算研究，以研究超分子嵌段共聚物的自组装，并为新聚合物材料的设计开发策略做出贡献。在广泛的单体之间可能的键能范围内扩展聚合物材料的范围是至关重要的，不仅可以创造新的结构，而且最重要的是获得以前未知的功能。超分子嵌段共聚物代表了一类这样的杂化键合聚合物，其中共价聚合物的结构单元通过超分子键连接成明确的结构。在可逆的超分子相互作用的辅助下，可以设想，与共价类似物相比，超分子嵌段共聚物自组装可能表现出更多样化的形态、刺激响应性和显著减少的退火时间/温度。然而，就基本方面而言，尚不清楚这些设想的功能和性质将通过何种机制实现。这对于非平衡条件下的自组装尤为重要，因为超分子嵌段共聚物的动态性质可能导致截然不同的自组装途径。缺乏对这些基本方面的理解，限制了实验开发具有可预测结构和动力学性质的杂化键合聚合物的努力，只能在狭窄的参数范围内逐个尝试。该项目旨在通过揭示超分子相互作用的可逆性与超分子嵌段共聚物自组装的结构和动力学行为之间的联系，从计算的角度解决这些未满足的需求。具体而言，本项目将考虑由共价二嵌段共聚物主链和低分子量低聚物添加剂端部通过超分子键连接到主链上而制成的超分子梳盘状二嵌段共聚物。自组装的超分子梳盘状嵌段共聚物是已知的产生具有内置功能的热响应的层次结构。本项目的重点是了解强而可逆的超分子键对微相热力学稳定性的影响，加工过程中结构形成的动力学，以及刺激响应结构转变的动力学途径。为了提供动力学研究的基础，首先确定了超分子梳盘状嵌段共聚物自组装的平衡形态。然后可以研究热退火过程中结构有序过程的动力学，并确定热响应有序转变的动力学途径。最小自由能路径将使用基于粒子的粗粒度计算机模拟来确定；它还将使超分子键对自组装的自由能景观的影响得以量化。基于最小自由能路径的自组装预测行为将在实验中得到验证，作为与实验组合作的一部分。该项目的结果将为设计具有适应性结构和动力学性能的新型聚合物材料提供策略。该项目由材料研究部通过凝聚态物质和材料理论项目以及促进竞争研究的既定项目（EPSCoR）共同资助。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。

NONTECHNICAL SUMMARY This award supports theoretical and computational research integrated with education to investigate how complex polymers assemble and contribute to developing design principles for complex polymer materials. Self-assembly is a process in which molecules or atoms organize as building blocks into ordered structures because of interactions among the components. This process occurs in the assembly of molecules or monomers into molecular building blocks that can themselves assemble in sequences to form long chain-like molecules known as polymers. Polymers are literally everywhere – they make up plants, plastics, the food we eat, and even our own bodies. Through increasingly precise control over the monomer sequences and molecular architectures, polymers have been transformed from large-scale commodity plastics into precision self-assembly building blocks that can undergo pre-programmed organization into materials with more complex structures. It is likely that further expanding the scope of polymers over a broad spectrum of possible bonding among monomers, new self-assembly processes can emerge, which will bring about functions that are unrealizable with conventional covalent polymers. The focus of this project is to study the process of self-assembly of the so-called supramolecular block copolymers -- a class of the “hybrid bonding” polymers made of structural units of covalent polymers connected into well-defined architectures through temperature-responsive reversible bonds. The PI aims to understand the fundamental connection between the reversibility of bonds at the molecular level and the temperature-responsive feature in the self-assembly process, both at equilibrium and in dynamical processes. By using computer simulations and quantifying the influence of the reversible bonds on the self-assembly process, this project is aimed to identify new pathways for making materials and for materials design. A goal is to formulate rules to incorporate predictable structural and kinetic properties into polymeric materials.As part of the educational component of the project, the PI aims to integrate classroom learning, research projects, and community service by developing a Community-Engaged Learning course “Introduction to the Mesoscale Simulations of Polymers for Engineering Applications" for senior undergraduates and graduate students. This effort will be in collaboration with the local water facility to test/develop wastewater treatments based on recyclable polymers. The goal of the Community-Engaged Learning course is three-fold: (1) to promote community awareness in training of the next-generation work force; (2) to cultivate and foster lasting partnership between the university and the city of Starkville; and (3) to develop technologies that are potentially beneficial to the local community.TECHNICAL SUMMARY This award supports theoretical and computational research integrated with education to investigate self-assembly of supramolecular block copolymers and contribute to developing strategies for the design of new polymeric materials. It is of central importance to expand the scope of polymeric materials over a broad spectrum of possible bonding energies among monomers, for not only creating novel structures but most importantly access to previously unknown functions. Supramolecular block copolymers represent a class of such hybrid bonding polymers in which structural units of covalent polymers are connected into well-defined architectures via supramolecular bonds. Assisted by the reversible supramolecular interactions, it is envisaged that supramolecular block copolymer self-assemblies may exhibit more diverse morphologies, stimuli-responsivity and dramatically reduced annealing times/temperatures comparing to their covalent analogues. In terms of the fundamental aspects, it is however unclear through what mechanisms these envisaged functions and properties will be brought about. It becomes particularly relevant for self-assemblies under nonequilibrium conditions, where the dynamic nature of supramolecular block copolymers may lead to dramatically different self-assembly pathways. A lack of understanding of these fundamental aspects had restricted efforts of experiment to develop hybrid bonding polymers with predictable structural and kinetic properties to case-by-case attempts within narrow parameter ranges. This project aims to address these unmet needs from a computational perspective, by revealing the link between reversibility of the supramolecular interactions and the structural and kinetic behaviors of supramolecular block copolymers self-assemblies. Specifically, this project will consider the supramolecular comb-coil diblock copolymers made of covalent diblock copolymer backbone and low-molar-mass oligomer additives end-attached to the backbone via supramolecular bonds. The self-assembly of supramolecular comb-coil deblock copolymers is known to produce thermo-responsive hierarchical structures with built-in functionality. The focus of this project is to understand the effects of the strong yet reversible supramolecular bonds on the thermodynamic stability of microphases, the kinetics of structure formation during processing, and the kinetic pathways for stimuli-responsive structure transitions. To provide the base for the kinetics studies, the equilibrium morphologies of the self-assembly of supramolecular comb-coil deblock copolymers will first be determined. The kinetics of the structure ordering process during the thermal annealing may then be investigated and kinetic pathways of the thermo-responsive order-order transitions will be determined. The minimum free energy path will be identified using particle-based coarse-grained computer simulations; it will also enable the influence of supramolecular bonds on the free-energy landscape of the self-assembly to be quantified. The predicted behaviors of the self-assembly based on the minimum free energy path will be verified in experiments as part of a collaboration with experiment groups. Results from this project will enable strategies for the design of new polymeric materials with adaptable structural and kinetic properties.This project is jointly funded by the Division of Materials Research through the Condensed Matter and Materials Theory program, and the Established Program to Stimulate Competitive Research (EPSCoR).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.