Friction Control by Adsorption of Polyelectrolyte-Grafted Nanoparticles

CBET-1133175 P.I.：Tilton，Robert D.智力优点：这项工作提供了一种新的边界润滑系统，以及对分子结构和分子间力联合收割机如何结合以最大限度地减少纳米结构有机/无机复合系统中的摩擦的新理解。因此，它体现了技术和科学的新奇。先前的基础研究已经表明，接枝在固体表面上的电刷大大减少了这些表面之间的粘附和摩擦。刷子是一层密集堆积的聚合物链分子，一端附着在表面上。 这些链从表面延伸数十纳米，形成一层保护层，抵抗其他表面的冲击。聚电解质是具有电荷的聚合物，这种电荷增强了链拉伸和表面保护特性。一个关键的挑战是，现有的方法，用于创建刷有缺点，限制了它们在工程应用中的使用。为了实现边界润滑的潜力，通过润滑刷，这项工作将提供一个全新的方式来部署这种刷在实际系统中。聚（2-（二甲基氨基）乙基甲基丙烯酸酯）接枝刷将在高，可控的接枝密度和可控的聚合度的二氧化硅纳米粒子接枝。这些接枝的纳米颗粒将用作预形成的刷元件。通过将它们悬浮在液相中，浸泡在待润滑的表面上，它们将吸附在这些表面上，并逐片形成稳定的刷涂层，以最大限度地减少摩擦。与其他用于创建密集型电刷的方法不同，这种方法可以应用于许多不同的材料类型和几何形状，并且还提供了在表面损坏后自我修复的新奇。 优化这种新型润滑系统激发了代表新工程科学的特定研究目标。 由于这种方法没有先例，因此设计了实验来揭示其摩擦控制机制。该研究计划将提供一个多尺度，定量结构与活性的关系，从纳米颗粒接枝链的构象和电离到表面层的多颗粒组织，最后到涂层表面之间的摩擦系数。这项工作使用了最先进的方法原子转移自由基聚合来创建接枝刷和胶体探针力显微镜来测量摩擦作为负载的函数。更广泛的影响：一个博士，一个MS多名本科生将通过本项目接受研究性教育。的博士学生将从与斯德哥尔摩研究人员国际合作经验中受益。将与一名小学科学教师一起编写关于摩擦和润滑的探索性科学课程，并通过教师培训网络传播。该研究项目将生产有效的水基润滑剂，以实用的方式利用电刷的低摩擦特性，这是目前电刷形成方法无法实现的。 例如，这将导致新的水基润滑剂被用作加工液。加工液往往会雾化到工作场所的空气中。因为它们将用水取代碳氢化合物，新的水基加工液将具有更低的职业健康风险和环境影响。 由于其固有的灵活应用模式，这种润滑策略还可以实现新的微机电系统（MEMS）技术，目前受到超小型化运动部件之间的摩擦和粘附的限制。 通过进一步的工作，这里开发的基本原理可以在未来转化为新的油基润滑剂，以改善发动机磨损和燃油效率。

CBET-1133175P.I.: Tilton, Robert D.Intellectual Merit:This work provides a new boundary lubricating system together with new understanding of how molecular structure and intermolecular forces combine to minimize friction in nanostructured organic/inorganic composite systems. It therefore embodies both technological and scientific novelty. Prior fundamental research has shown that polyelectrolyte brushes grafted on solid surfaces greatly diminish adhesion and friction between those surfaces. Brushes are descriptively named layers of densely packed polymer chain molecules attached by one end to a surface. The chains stretch tens of nanometers away from the surface to form a protective coating that resists impact by other surfaces. Polyelectrolytes are polymers that have electrical charge, and this charge strengthens chain stretching and surface protection characteristics. A critical challenge is that existing methods for creating brushes have shortcomings that limit their uses in engineering applications. In order to realize the potential of boundary lubrication by polyelectrolyte brushes, this work will provide a fundamentally new way to deploy such brushes in practical systems. Poly(2-(dimethylamino)ethyl methacrylate) polyelectrolyte brushes will be grafted from silica nanoparticles at high, controlled grafting densities and controlled degrees of polymerization. These grafted nanoparticles will serve as pre-formed brush elements. By suspending them in the liquid phase bathing the surfaces to be lubricated, they will adsorb onto those surfaces and create stable brush coatings, piece by piece, to minimize friction. Unlike other methods for creating dense polyelectrolyte brushes, this approach can be applied to many different material types and geometries and also offers the novelty of self-healing after surface damage. Optimizing this new lubrication system motivates specific research aims that represent novel engineering science. Since there is no precedent for this approach, experiments are designed to reveal its mechanisms for friction control. The research plan will provide a multi-scale, quantitative structure versus activity relationship spanning from the conformation and ionization of nanoparticle-grafted polyelectrolyte chains to the multiparticle organization of surface layers and finally to the friction coefficient between coated surfaces. The work uses state of the art methods atom transfer radical polymerization to create grafted polyelectrolyte brushes and colloidal probe force microscopy to measure friction as a function of load.Broader Impacts:One Ph.D., one M.S. and several undergraduate students will receive research education through this project. The Ph.D. student will benefit from an international collaboration experience with researchers in Stockholm. Discovery-based science lessons on friction and lubrication will be developed with an elementary science teacher and disseminated through teacher training networks. The research project will produce effective water-based lubrication agents that exploit the low friction properties of polyelectrolyte brushes in a practical manner that cannot be achieved with current methods of brush formation. This will lead to new water-based lubricants to be used as machining fluids, for example. Machining fluids tend to be atomized into the workplace air. Because they would replace hydrocarbons with water, new water-based machining fluids would have lower occupational health risks and environmental impacts. Because of its inherently flexible mode of application, this lubrication strategy may also enable new microelectromechanical system (MEMS) technologies that currently are limited by friction and adhesion between ultraminiaturized moving parts. With further work, the basic principles developed here can be translated in the future to new oil-based lubricants to improve engine wear and fuel efficiency.