Characterization of Hydrodynamics and Behavior of Viscoelasticity at the Nanoscale

在非常小的尺度上测量材料物理性质的能力是推进科学研究和技术进步的关键。发生在纳米尺度上的测量具有特别重要的意义，其中涉及的物理尺寸约为十亿分之一米。原子力显微镜(AFM)是在纳米尺度上定量测量材料性质的主要工具之一。然而，在纳米尺度上存在许多物理现象，阻碍了准确的定量测量，特别是在液体环境中。该项目旨在了解和充分描述两种这样的现象：原子力显微镜在液体环境中操作时在纳米尺度上产生的流体力(流体动力学)和支配被询问材料行为的基本原理(粘弹性)。该项目将能够在纳米尺度上对各种无机和生物材料在液体环境中的材料性质进行定量测量。这将使医学、生物和材料工程等领域的新的尖端研究成为可能。此外，该项目的教育计划将开发一个动手、互动和便携的学习平台，使K-12、本科生和研究生接触AFM及其操作中使用的科学原理。该教育计划将引起人们对STEM领域的更多兴趣和保留。这个项目的主要目标是通过建立数学和数值模型来捕捉和量化这些现象，以了解纳米级复杂样品的粘弹性和流体动力性对测量系统共振行为的影响。这些效应可以通过接触共振(CR)光谱AFM的透镜来解决。CR光谱系统是了解这些现象的理想测量平台，因为它在没有这些影响的情况下很容易被理解，并且能够询问感兴趣的流体动力学和粘弹性参数空间。该项目的重点是准确预测CR光谱系统中存在的三维流体-结构相互作用，为CR光谱建立材料模型以解释生物和非经典粘弹性材料，并通过实验验证流体-结构相互作用和粘弹性模型。该项目的成功将使基于接触共振的生物材料在液体环境中的定量纳米机械表征成为可能，这反过来又将促进几个关键领域的研究，如生物材料和生物聚合物的研究及其在医学界的应用，骨关节炎骨骼中纳米机械结构变化的研究，以及牙本质和牙釉质的研究。

The ability to measure physical properties of materials at very small scales is key to advancing scientific research and technological progress. Measurements that occur at the nanoscale, where the physical dimensions involved are on the order of one billionth of a meter, are of particular importance. The atomic force microscope (AFM) is one of the primary tools for making quantitative measurements of material properties at the nanoscale. However, there exist many physical phenomena at the nanoscale that prevent accurate quantitative measurements from being made, especially in liquid environments. This project aims to understand and fully characterize two such phenomena: fluid forces that arise at the nanoscale when the AFM is operated in liquid environments (hydrodynamics) and the underlying principles that govern the behavior of the material being interrogated (viscoelasticity). This project will enable quantitative measurements of material properties at the nanoscale in liquid environments on a variety of inorganic and biological materials. This will enable new and cutting-edge research in areas such as medicine, biology, and materials engineering. In addition, the project's educational plan will develop a hands-on, interactive, and portable learning platform that will expose K-12, undergraduate, and graduate students to AFM and the scientific principles used in its operation. The educational plan will engender further interest and retention in the STEM fields. The primary objective of this project is to understand the effect that complex sample viscoelasticity and hydrodynamic forces at the nanoscale have on the resonant behavior of measurement systems by developing mathematical and numerical models that capture and quantify these phenomena. These effects can be addressed through the lens of contact resonance (CR) spectroscopy AFM. The CR spectroscopy system is an ideal measurement platform to understand these phenomena because it is well understood in the absence of these effects and has the ability to interrogate both the hydrodynamic and viscoelastic parameter spaces of interest. The focus of this project is on accurately predicting the three-dimensional fluid-structure interactions present in CR spectroscopy systems, establishing material models for CR spectroscopy to account for biological and non-classical viscoelastic materials, and experimentally validating the fluid-structure interaction and viscoelastic models. The success of the project will enable accurate contact resonance based quantitative nanomechanical characterization of biological materials in liquid environments, which in turn will facilitate research in several key areas such as study of biomaterials and bio-polymers with applications to the medical community, study of nanomechanical structural changes in osteoarthritic bones, and study of dentin and tooth enamel.