SGER: Use of Phase Imaging in Atomic Force Microscopy for Measurement of Viscoelastic Contrast in Polymer Nanocomposites and Molecularly-Thick Lubricant Films

SGER：使用原子力显微镜中的相位成像来测量聚合物纳米复合材料和分子厚润滑油膜中的粘弹性对比度

• 批准号: 0226066
• 负责人: Bharat Bhushan
• 金额: --
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-12-01 至 2004-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0226066&HistoricalAwards=false
• 关键词: SGER; Use; Phase; Imaging; Atomic

Small Grant for Exploratory Research (SGER) Use of Phase Imaging in Atomic Force Microscopy for Measurement of Viscoelastic Contrast in Polymer Nanocomposites and Molecularly-Thick Lubricant Films In the proposed work our goal is the development of a technique for quantitative imaging of viscoelastic properties across polymer nanocomposite bearing surfaces and surfaces lubricated with ultrathin films. This would be an important technological advancement that would provide a tool for measurement and optimization of polymer nanocomposites and a tool for measurement of lubricant film uniformity. Such a tool would be particularly important for MEMS and magnetic storage. So this project has a very high potential payoff. Although this is a high risk project (because such a technique has never been developed before), we have seen promising results in our preliminary experiments. Much more work must be carried out however. Preliminary studies of phase contrast, using an atomic force microscope (AFM) in both tapping and force modulation modes have shown that different regimes exist. Different AFM cantilever/tip vibration amplitudes and tip-sample surface separation distances give different phase contrast images. We believe that hard tapping conditions, i.e. high cantilever/tip vibration amplitude and low tip-sample surface separation, give phase images that emphasize viscoelastic properties, which are important in polymers. In commercial magnetic particulate tapes and polymer films with hard embedded particles, high phase contrast is found. The hard particles give lower phase lag than the surrounding polymer at hard tapping conditions, as expected. In the proposed research we will develop the technique with phase contrast measurements. We will make simultaneous measurements using several well-established AFM techniques: friction force (for contrast based on differences in lubricity among materials), force modulation (for contrast based on stiffness differences), and Kelvin probe (for contrast based on surface potential differences) microscopies. These should provide insight into the results of the phase contrast technique that is being developed here.We also seek to quantify results. We will attempt to relate phase data from the AFM for thin polymer samples to viscoelasticity data obtained for these samples by another proven technique known as dynamic mechanical analysis (DMA). In the DMA thin polymer samples are subjected to tension/compression strain cycles and the corresponding stress is measured. The phase lag between the stress and strain is then found. If the AFM is truly measuring viscoelastic properties then it should be possible to find a correlation between loss tangent from the DMA and phase lag from the AFM. In order to quantify, it will be necessary to understand the physics of the contact. To this end we will develop a vibration model that accounts for the repulsive and attractive forces between the tip and the dissipation caused by the viscoelasticity of the sample.An award would support one graduate student and partially support one postdoctoral researcher. This would provide an opportunity to recruit and fund a minority or woman. The PI and his department have made efforts to attract such students in recent years. The department regularly invites, and provides travel grants for, students, particularly women and minorities, from other schools to attract them for graduate studies; we have had some success in this. Undergraduate students would work on the project as well. Projects like these provide hands-on opportunities for undergraduate students in a high-tech lab. Past undergraduates in the PI's lab have actually coauthored articles for technical journals. This project will provide additional material for the PI's course on tribology and in soon-to-be-developed nanoscale courses.

在我们提出的工作中，我们的目标是开发一种技术，用于聚合物纳米复合材料承载表面和超薄薄膜润滑表面的粘弹性特性的定量成像。这将是一项重要的技术进步，将为聚合物纳米复合材料的测量和优化提供工具，并为测量润滑油膜均匀性提供工具。这种工具对于MEMS和磁存储尤其重要。所以这个项目有很高的潜在回报。虽然这是一个高风险的项目（因为以前从未开发过这种技术），但我们在初步实验中看到了有希望的结果。然而，必须进行更多的工作。利用原子力显微镜（AFM）在攻丝和力调制两种模式下进行的相位对比的初步研究表明，存在不同的机制。不同的AFM悬臂梁/针尖振动幅值和针尖-样品表面分离距离会产生不同的相对比图像。我们认为，硬攻丝条件，即高悬臂/尖端振动振幅和低尖端样品表面分离，给出了强调粘弹性特性的相图像，这在聚合物中很重要。在商用磁颗粒带和硬嵌入颗粒的聚合物薄膜中，发现了高相衬。正如预期的那样，硬颗粒在硬攻丝条件下比周围的聚合物具有更低的相位滞后。在提出的研究中，我们将发展相衬测量技术。我们将使用几种成熟的AFM技术进行同步测量：摩擦力（基于材料之间的润滑差异进行对比），力调制（基于刚度差异进行对比）和开尔文探针（基于表面电位差进行对比）显微镜。这些应该能让我们深入了解这里正在开发的相衬技术的结果。我们还寻求量化结果。我们将尝试将薄聚合物样品的AFM相数据与通过另一种被称为动态力学分析（DMA）的成熟技术获得的这些样品的粘弹性数据联系起来。在DMA中，薄聚合物样品经受拉伸/压缩应变循环，并测量相应的应力。然后发现应力和应变之间的相位滞后。如果AFM真的是在测量粘弹性特性，那么应该有可能找到DMA的正切损耗与AFM的相位滞后之间的相关性。为了量化，有必要了解接触的物理性质。为此，我们将开发一个振动模型，该模型考虑了尖端之间的排斥力和吸引力以及样品粘弹性引起的耗散。一个奖项将支持一名研究生，并部分支持一名博士后研究员。这将为招募和资助少数民族或妇女提供机会。近年来，PI和他的部门一直在努力吸引这类学生。该系定期邀请其他学校的学生，特别是妇女和少数民族学生，并为他们提供旅费补助金，以吸引他们进行研究生学习；我们在这方面取得了一些成功。本科生也会参与这个项目。像这样的项目为本科生提供了在高科技实验室动手的机会。PI实验室过去的本科生实际上已经与人合作为技术期刊撰写了文章。该项目将为PI的摩擦学课程和即将开发的纳米课程提供额外的材料。