Molecular Scale Characterization of Sheared Interfaces by Combined Time-Resolved Neutron Reflectometry and Polarized Infrared Spectroscopy: From polymer brushes to lipid multilayers

通过时间分辨中子反射计和偏振红外光谱相结合对剪切界面进行分子尺度表征：从聚合物刷到脂质多层

• 批准号: 505669720
• 负责人: Professor Dr. Reiner Dahint
• 金额: --
• 依托单位: Laboratoire de Physique de Solides - UMR 8502
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/505669720?language=en
• 关键词: Molecular; Scale; Characterization; Sheared; Interfaces

Shear is a widespread phenomenon in nature and technology, and can significantly alter the structure, function and performance of biological and artificial systems. E.g. joint movement is accompanied by shear and friction forces which can lead to joint wear and osteoarthritis. Biological cells respond to mechanical stress exerted by liquid flow in vessels by changing their morphology and metabolism, and reduction of friction by lubricants and surface coatings is important to reduce energy consumption and increase the lifetime of almost any machine with moving parts. To understand, control and utilize the effects of shear, it is highly desirable to analyze its impact on the structure and function of the sheared interfaces on a molecular scale. For this purpose, we will combine in situ neutron reflectometry (NR) and infrared (IR) spectroscopy to follow shear-induced interfacial processes with time resolution down to about 10 ms. NR is an excellent tool for structural investigation of buried interfaces, allowing extraction of isotope-sensitive density profiles at interfaces down to atomic resolution. However, it does not provide chemical and molecular information, which will, thus, be obtained by IR spectroscopy. Using polarization analysis, IR spectroscopy will also provide insight into the molecular orientation of sheared interfacial films. Interfacial films are often composed of different types of molecules. Here, the problem arises to differentiate between their individual behavior in response to shear, in particular, if they are chemically similar (e.g. different biomolecules with similar backbone or chains) or even identical (e.g. entangled polymer chains of the same type but surface-anchored or free). A major goal of the studies is, therefore, to discriminate the shear-induced behavior of such complex interfaces by deliberately deuterating one of the species involved. In case of NR, specific molecules will be highlighted due to altered scattering length density. In IR spectroscopy, deuteration will shift the respective bands to lower wavenumbers allowing discriminating between deuterated and protonated species. Based on model systems, the French and German partners will jointly investigate two shear phenomena of high technical and biomedical relevance, respectively: i) the molecular origin of shear-dependent friction of entangled polymeric liquids at solid walls, which has been proposed to arise from surface-adsorbed chains and a coil-to-stretch transition of the latter, resulting in a subsequent disentanglement with the free flowing chains beyond a critical stress, and ii) the response of lubricating films in mammalian joints to shear forces in order to elucidate the mechanisms of osteoarthritis and related medical cures. For these studies, a specialized shear cell will be designed which allows for parallel time-resolved NR and IR measurements in situ, and the generation of complex shear patterns (start-stop, oscillatory, etc.).

剪切是自然界和技术中普遍存在的现象，可以显著改变生物和人工系统的结构、功能和性能。例如，关节运动伴随着剪切力和摩擦力，这可能导致关节磨损和骨关节炎。生物细胞通过改变其形态和代谢来响应容器中液体流动所施加的机械应力，并且通过润滑剂和表面涂层减少摩擦对于减少能耗和增加几乎任何具有运动部件的机器的寿命都很重要。为了理解、控制和利用剪切效应，在分子尺度上分析其对剪切界面结构和功能的影响是非常必要的。为此，我们将结合联合收割机在原位中子反射（NR）和红外（IR）光谱，以遵循剪切引起的界面过程的时间分辨率下降到约10毫秒。NR是一个很好的工具，埋界面的结构调查，允许提取同位素敏感的密度分布在接口下降到原子分辨率。然而，它不提供化学和分子信息，因此，将通过IR光谱获得。使用偏振分析，红外光谱也将提供洞察剪切界面膜的分子取向。界面膜通常由不同类型的分子组成。这里，出现了区分它们响应于剪切的个体行为的问题，特别是如果它们在化学上相似（例如，具有相似主链或链的不同生物分子）或甚至相同（例如，相同类型但表面锚定或自由的缠结聚合物链）。因此，研究的一个主要目标是通过故意使所涉及的物种之一氘化来区分这种复杂界面的剪切诱导行为。在NR的情况下，由于散射长度密度的改变，特定分子将被突出显示。在红外光谱中，氘化将使相应的谱带移动到较低的波数，从而允许区分氘化和质子化物质。基于模型系统，法国和德国合作伙伴将分别联合研究两种具有高度技术和生物医学相关性的剪切现象：i）缠结的聚合物液体在固体壁处的剪切依赖性摩擦的分子起源，其已经被提出是由表面吸附的链和后者的线圈到拉伸转变引起的，导致随后与自由流动链的解缠结超过临界应力，和ii）哺乳动物关节中的润滑膜对剪切力的响应，以阐明骨关节炎和相关医学治疗的机制。对于这些研究，将设计一个专门的剪切单元，允许并行的时间分辨NR和IR原位测量，并产生复杂的剪切模式（起止，振荡等）。