Development of Smart Nanotribological Surfaces using Multifunctionalized Mesoporous Nanosphere Films

利用多功能介孔纳米球薄膜开发智能纳米摩擦学表面随着当前技术的发展，在各种工程实践中，特别是在微/纳米系统中，对将摩擦学现象(摩擦、磨损和润滑)控制在所需水平上提出了更严格的要求。传统的摩擦学系统表现出两个弱点--无法适应运行条件的变化以提供统一的摩擦学响应，以及摩擦学界面的持久性。设计一种“智能”的薄膜，使其表现出适应操作条件变化的“自我修复”或“自我修复”行为，将是非常有益的。介孔纳米球材料是一类新型的材料，其内孔和外表面具有高度的分子设计可控性，可用于实现摩擦学薄膜的自适应和自修复。本研究的目标是设计新型的摩擦学涂层/薄膜系统，利用介孔二氧化硅/氧化铝纳米球材料(I)在微米/纳米尺度上提供优异的摩擦学性能；(Ii)对运行条件的变化具有自适应(‘SMART’)；(Iii)自我修复，以在摩擦学性能中提供更高的耐久性和寿命。每个阶段包括化学合成、沉积以及对每个材料系统的化学、结构、机械和摩擦学评估。拟议研究计划的第一阶段涉及合成和沉积紧密堆积的与衬底刚性连接的MNM的单分子层。第二阶段涉及使用以下方法设计自适应薄膜：(A)使用含有热敏聚合物(聚-(N-异丙基丙烯酰胺)(PNIPAAm))的接枝单分子膜进行内部功能化的自适应薄膜设计，这将导致聚合物的低临界溶液温度(LCST)以下和之上的表面的摩擦响应发生变化；(B)利用MoS2和石墨化的碳纳米颗粒的自润滑混合自组装单分子层-纳米粒子表面。纳米颗粒在自然界中分别在低湿度和高湿度下具有自润滑性，将有助于保持表面的均匀摩擦响应。第三阶段涉及设计一种包含自组装单分子层(SAM)和MNMs的“自修复”摩擦学表面-将使用光刻和SAM化学方法制造覆盖有MNm口袋的SAM表面。MNMS将在外部功能化，具有与表面SAM相似的摩擦学特性的聚合层，而内部孔将在溶液中容纳游离的SAM分子。磨损或表面断裂引发的SAM分子的释放将允许分子主动吸附到磨损的部位，从而执行‘自我修复’的行动。微/纳米级别的摩擦学表征将使用原子力显微镜和PI实验室开发的微摩擦学技术进行，而MNM薄膜的合成将通过共同PI建立的技术进行。跨学科研究工作的智力优势包括开发新的和创新的设计策略来生产“智能”摩擦学表面，以及更好地了解与材料分子设计和摩擦学行为相关的化学和物理现象。这种“智能”系统的实现将为摩擦学对带来极大的回报，这些摩擦学对受到多重和重复的环境变化的影响，并要求非常高的耐用性，这可能发生在消费、国防、航空航天和医疗应用中。此外，这项研究还展示了分子设计策略，这些策略提供了在定制最终系统的结构和行为时获得高度控制的方法。两名博士生将参与这个项目。他们将接触到跨学科的研究，并从学习经验中受益。为了加强妇女和少数族裔学生对研究生教育和研究的参与，来自这些代表性不足群体的学生将成为该项目工作的对象。研究成果将被传播到几个由专业督学教授的机械工程和化学的本科生和研究生课程中，这将加强每年约200名学生的教育。拟议活动的广泛影响是：(1)研究活动促进系统设计方面的跨学科研究工作，可导致在广泛的应用中为优越的摩擦学接口提出新的工程战略；(2)研究活动通过有针对性的招聘工作促进妇女和/或少数族裔学生的更多参与；(3)研究活动通过强调跨学科研究和纳米级设计战略的重要性，加强爱荷华州立大学两个系的本科生和研究生的教育。

Development of Smart Nanotribological Surfaces using Multifunctionalized MesoporousNanosphere FilmsWith the current development of technology, a stricter requirement for controlling tribological phenomena (friction, wear and lubrication) at desired levels is arising in various engineering practices, especially in micro/nanoscale systems. Traditional tribological systems exhibit two weaknesses - the inability to adapt to changes in operating conditions to provide uniform tribological response and the durability of the tribological interface. Designing 'smart' films that exhibit self-adapting behavior to changes in operating conditions 'self-repairing' or 'self-healing' behavior would be extremely beneficial. Mesoporous Nanosphere Materials (MNMs) are a novel class of materials that exhibit a high degree of molecular design control of its internal pores and external surfaces, which can be taken advantage of to realize tribological films that are adaptive and self-healing.The research objectives of this proposal are to design novel tribological coatings/film systems utilizing mesoporous silica/alumina nanosphere materials that (i) can provide superior tribological performance formicro/nanoscale applications; (ii) are self-adapting ('smart') to changes in operating conditions and (iii) are self-healing to provide enhanced durability and longevity in tribological performance. Each phase involves chemical synthesis, deposition and chemical, structural, mechanical and tribological evaluation of each material system. The first phase of the proposed research program involves the synthesis and deposition of a closely packed monolayer of MNMs that are rigidly linked to the substrate. The second phase involves designing self-adaptive films using (a) MNMs that are internally functionalized using grafted monolayers incorporating a thermosensitive polymer (Poly-(N-isopropylacrylamide) (PNIPAAm)) which will cause a change in the frictional response of the surface below and above the lower critical solution temperature (LCST) of the polymer; (b) a self-lubricating hybrid self-assembled monolayer-nanoparticle surface utilizing MoS2 and graphitized carbon nanoparticles. The nanoparticles, being self-lubricating in nature at low and high humidity respectively, will aid in maintaining a uniform friction response of the surface. The third phase involves the design of a 'self-healing' tribological surface incorporating self-assembled monolayers (SAMs) and MNMs - a SAM covered surface with pockets of MNMs will be fabricated using photolithography and SAM chemistry. The MNMs will be externally functionalized with a polymer layer with tribological characteristics similar to that of the surface SAMs while internal pores will house free SAM molecules in solution. Wear or surface fracture initiated release of SAM molecules will allow active adsorption of molecules onto worn sites thus performing a 'self-healing' action. Micro/nanoscale tribological characterization will be performed using atomic force microscopy and microtribometry techniques developed at the PI's laboratory while synthesis of MNM films will be performed via techniques established by the co-PI.The intellectual merits of the interdisciplinary research efforts include the development of novel and innovative design strategies to produce 'smart' tribological surfaces and obtaining a better understanding of chemical and physical phenomena associated with molecular design of materials and tribological behavior. The realization of such 'smart' systems would be extremely rewarding for tribological pairs subjected to multiple and repeated environmental changes and which require very high durability, which can occur in consumer, defense, aerospace and medical applications. In addition, the research demonstrates molecular design strategies that provide ways to obtain a high degree of control in tailoring the structure and behavior of the final system. Two Ph.D. students will work on the project. They will be exposed to cross-disciplinary research and benefit from the learning experience. In order to enhance the participation of women and minority students in graduate education and research, students from these underrepresented groups will be targeted for work on the project. Research results will be disseminated into several undergraduate and graduate courses being taught by the PIs in Mechanical Engineering and Chemistry that will enhance the education of about 200 students every year. The broad impacts of the proposed activities are (i) the research activities promote interdisciplinary research efforts in system design that can lead to novel engineering strategies for superior tribological interfaces in a wide range of applications (ii) they promote increased participation of women and/or minority students through targeted recruitment efforts and (iii) the research activities enhance the education of undergraduate and graduate students of two departments at Iowa State University by emphasizing the importance of interdisciplinary research and nanoscale design strategies.