Development of Smart Nanotribological Surfaces using Multifunctionalized Mesoporous Nanosphere Films

利用多功能介孔纳米球膜开发智能纳米摩擦学表面随着技术的发展，在各种工程实践中，特别是在微/纳米尺度系统中，对控制摩擦、磨损和润滑现象提出了更严格的要求。传统的摩擦学系统有两个缺点：不能适应工作条件的变化，不能提供均匀的摩擦学响应，不能保证摩擦学界面的耐用性。设计“智能”薄膜，表现出对操作条件变化的自适应行为，“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（MNMs）是一类新型材料，其内部孔和外部表面具有高度的分子设计控制，可以用来实现自适应和自修复的摩擦学膜。本提案的研究目标是利用介孔二氧化硅/氧化铝纳米球材料设计新的摩擦学涂层/薄膜系统，(i)可以在微/纳米级应用中提供卓越的摩擦学性能；（ii）能够自适应（“智能”）操作条件的变化；（iii）能够自我修复，提高摩擦性能的耐久性和使用寿命。每个阶段涉及化学合成，沉积和化学，结构，机械和摩擦学评价每个材料体系。拟议研究计划的第一阶段包括合成和沉积紧密堆积的单层纳米颗粒，该单层纳米颗粒与基板紧密相连。第二阶段涉及设计自适应薄膜，使用(a) MNMs，其内部功能化使用含有热敏聚合物（聚n -异丙基丙烯酰胺（PNIPAAm））的接枝单层，这将导致表面摩擦响应的变化低于和高于聚合物的低临界溶液温度（LCST）；(b)利用二硫化钼和石墨化碳纳米颗粒的自润滑自组装单层纳米颗粒表面。纳米颗粒在低湿度和高湿度下具有自润滑性质，将有助于保持表面的均匀摩擦响应。第三阶段涉及“自修复”摩擦学表面的设计，包括自组装单层（SAM）和mnm - SAM覆盖表面的mnm口袋将使用光刻和SAM化学制造。MNMs将在外部功能化，具有与表面SAMs相似的摩擦学特性的聚合物层，而内部孔隙将容纳溶液中的自由SAM分子。磨损或表面断裂引发的SAM分子释放将允许分子主动吸附到磨损部位，从而执行“自我修复”作用。微/纳米尺度的摩擦学表征将使用PI实验室开发的原子力显微镜和微摩擦学技术进行，而MNM薄膜的合成将通过co-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颖和创新的设计策略，以生产“智能”摩擦学表面，并更好地理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”系统的实现对于承受多次和反复环境变化的摩擦学副来说是非常有益的，并且需要非常高的耐用性，这可能发生在消费，国防，航空航天和医疗应用中。此外，该研究还展示了分子设计策略，提供了在定制最终系统的结构和行为方面获得高度控制的方法。两名博士生将参与该项目。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民族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的工作对象。研究成果将会应用于机械工程和化学专业的几门本科和研究生课程中，每年约有200名学生从中受益。拟议活动的广泛影响是：(i)研究活动促进了系统设计中的跨学科研究工作，可以在广泛的应用中为卓越的摩擦学界面带来新的工程策略；（ii）通过有针对性的招聘工作，促进了女性和/或少数民族学生的参与；（iii）研究活动加强了爱荷华州立大学两个系的本科生和研究生的教育强调跨学科研究和纳米级设计策略的重要性。

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.