Chemomechanics: a bridge across the formidable gap

该提案的总体目标是通过实验验证，并将理解和利用聚合物材料对机械载荷的化学反应的概念框架带到一个新的实用水平。 聚合物材料的巨大技术重要性主要是由于它们的机械性能的显著范围，即，它们对机械负荷的反应。在宏观尺度上，这种载荷（应力）改变了物体的整体形状，但材料响应在长度和时间上跨越许多数量级。几乎就在聚合物的性质被认识到时，对聚合物固体、熔体或溶液的某些简单操作就被证明会导致聚合物骨架的断裂，而无需强共价键以可检测的速率断裂通常所需的高温。这种效应通常被称为机械化学。机械化学被认为在控制（1）裂纹扩展和灾难性材料失效，（2）微流体诊断和高效色谱中表面锚定聚合物的稳定性，以及（3）脱盐膜、抗冲击材料（例如，防弹背心）和轮胎;以及在影响技术过程中如（4）喷射注射（例如，在有机电子设备中的喷墨材料沉积期间），（5）聚合物熔融加工，（6）高性能润滑，（7）提高的油回收（例如，聚合物驱油），（8）湍流减阻（例如，管道、消防、灌溉）。利用局部反应性和机械负载之间的耦合既可以推进这些技术，又可以产生全新的材料和工艺，包括聚合物光致动（即，将光直接转换为运动以驱动自主纳米机械装置、控制光学计算中的信息流、在太阳能捕获方案中定位反射镜或光伏电池）、有效捕获废机械能、能够自主报告内应力和自我修复的材料以及在亚纳米尺度上研究聚合物动力学的工具。 为了充分实现这一巨大的潜力，材料科学界需要一套理论的，计算的，合成和物理化学工具和模型，以指导我们努力确定单体和聚合物结构的化学组成和分子结构，产生具有所需应力响应特性的块状材料，并使聚合物动力学的分子研究，特别是在5 - 100 nm的长度尺度（即所谓的“巨大差距”）。实现这一目标需要对定义机械载荷的宏观参数（例如，应力或应变张量）和控制化学反应性变化的分子性质（例如，活化能）。EPSRC的资助将使我们能够通过一个整合（大）分子设计和合成，物理测量（使用各种现代光谱技术，包括单分子力谱和高分辨率X射线光电子能谱），仪器设计，量子化学计算，物理力学和有限元建模和理论的计划来发展这种理解。 为了实现这一总体目标，我们将使用一系列反应性单体，这些单体是专门设计用于有效和准确的局部反应性动力学测量以及对整个物理系统的结果进行分子解释的，这些物理系统的行为受拉伸大分子动力学的支配。这些系统的范围从单独的隔离拉伸聚合物链一直到负载下的块状无定形聚合物。

The overarching objective of this proposal is to validate experimentally and bring to a new level of utility a conceptual framework for understanding and exploiting the chemical response of polymeric materials to mechanical loads. The enormous technological importance of polymeric materials is due largely to the remarkable range of their mechanical properties, i.e., their responses to mechanical loads. At the macroscopic scale such loads (stresses) change bulk shapes of objects, but the material response extends across many orders of magnitude in length and time. Almost as soon as the nature of polymers had been recognized certain simple manipulations of polymer solids, melts or solutions were shown to result in fragmentation of polymer backbones without the high temperatures that are normally required for strong covalent bonds to break at detectable rates. The effect is often called mechanochemistry. Mechanochemistry is thought to be important in controlling (1) crack propagation and catastrophic materials failure, (2) stability of surface-anchored polymers in microfluidic diagnostics and high-performance chromatography and (3) behavior of desalination membranes, impact-resistant materials (e.g., bulletproof vests) and tires; and in affecting technological processes as diverse as (4) jet injection (e.g., during inkjet material deposition in organic electronics), (5) polymer melt processing, (6) high-performance lubrication, (7) enhanced oil recovery (e.g., polymer flooding), (8) turbulence drag reduction (e.g., in pipelines, fire fighting, irrigation). Exploiting coupling between localized reactivity and mechanical loads could both advance these technologies and yield fundamentally new materials and processes, including polymer photoactuation (i.e., direct conversion of light into motion to power autonomous nanomechanical devices, control information flow in optical computing, position mirrors or photovoltaic cells in solar capture schemes), efficient capture of waste mechanical energy, materials capable of autonomous reporting of internal stresses and self-healing and tools to study polymer dynamics at sub-nm scales. To realize this remarkable potential fully the materials science community needs a set of theoretical, computational, synthetic and physicochemical tools and models to guide our effort to identify chemical compositions and molecular structures of monomers and polymer architectures that yield bulk materials with desired stress-responsive characteristics and to enable molecular studies of polymer dynamics particularly at the 5-100 nm lengthscale (the so called "formidable gap"). Achieving this goal requires a general, quantitative understanding of the relationship between the macroscopic parameters that define mechanical loads (e.g., stress or strain tensors) and the molecular properties that govern the changes in chemical reactivity (e.g., energies of activation). EPSRC funding will enable us to develop such understanding with a program that integrates (macro)molecular design and synthesis, physical measurements (using a variety of modern spectroscopic techniques, including single-molecule force spectroscopy and high-resolution X-ray photoelectron spectroscopy), instrument design, quantum-chemical computations, statistical-mechanics and finite-element modeling and theory. To accomplish this overall objective we will use a series of reactive monomers specifically designed for efficient and accurate kinetic measurements of localized reactivity and molecular interpretation of the results across the whole range of physical systems whose behavior is governed by dynamics of stretched macromolecules. These systems range from individual isolated stretched polymer chains all the way to bulk amorphous polymers under load.