Friction Control by Adsorption of Polyelectrolyte-Grafted Nanoparticles

生态旅游- 1133175 - p。知识价值：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如何结合在一起以减少纳米结构有机/无机复合材料系统中的摩擦的新理解。因此，它体现了技术和科学的新颖性。先前的基础研究表明，接枝在固体表面上的聚电解质电刷大大减少了固体表面之间的粘附和摩擦。刷被描述为由一端附着在表面上的密集排列的聚合物链分子层。这些链从表面延伸数十纳米，形成一层保护涂层，可以抵抗其他表面的冲击。聚电解质是带有电荷的聚合物，这种电荷加强了链的拉伸和表面保护特性。一个关键的挑战是，现有的制造刷子的方法有缺点，限制了它们在工程应用中的应用。为了实现聚电解质刷的边界润滑潜力，本工作将为在实际系统中部署这种刷提供一种全新的方法。聚（2-（二甲氨基）甲基丙烯酸乙酯）聚电解质电刷将在高、可控的接枝密度和可控的聚合度下从二氧化硅纳米颗粒接枝。这些接枝的纳米颗粒将作为预先形成的刷元件。通过将它们悬浮在需要润滑的表面的液相中，它们将被吸附在这些表面上，并一块一块地形成稳定的刷涂层，以减少摩擦。与其他制造密集聚电解质电刷的方法不同，这种方法可以应用于许多不同的材料类型和几何形状，并且还提供了表面损伤后自愈的新颖性。优化这种新的润滑系统激发了特定的研究目标，代表了新的工程科学。由于这种方法没有先例，实验旨在揭示其摩擦控制机制。该研究计划将提供一个多尺度、定量的结构与活性的关系，从纳米颗粒接枝的聚电解质链的构象和电离到表面层的多粒子组织，最后到涂覆表面之间的摩擦系数。这项工作使用最先进的原子转移自由基聚合方法来制造接枝聚电解质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：将有1名博士、1名硕士和数名本科生通过本项目接受研究教育。博士生将受益于与斯德哥尔摩研究人员的国际合作经验。关于摩擦和润滑的基于发现的科学课程将由一名小学科学教师编写，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，以一种实用的方式利用聚电解质刷的低摩擦特性，这是目前的刷形成方法无法实现的。这将导致新的水基润滑剂被用作加工流体，例如。加工液往往被雾化到工作场所的空气中。由于新型水基加工液将用水取代碳氢化合物，因此其职业健康风险和对环境的影响将会降低。由于其固有的灵活应用模式，这种润滑策略也可以使新的微机电系统（MEMS）技术成为可能，这些技术目前受到超小型化运动部件之间摩擦和粘附的限制。随着进一步的工作，这里开发的基本原理可以在未来转化为新的油基润滑油，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.