Development of Smart Nanotribological Surfaces using Multifunctionalized Mesoporous Nanosphere Films
With 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 for micro/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.
