Understanding and Leveraging the Effect of Nanoscale Roughness on Macroscale Adhesion

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Many of the modern technologies produce miniaturized devices used in applications from electronics, communications, medicine as well as others. The small size of these devices leads to unique issues in their manufacture and use. However, many of these emerging devices and manufacturing techniques face a problem with stickiness or adhesion. Specifically, when small-size parts come into contact, they spontaneously stick together and cannot easily be pulled apart. This problem significantly limits the performance and reliability of otherwise promising technologies. This grant supports fundamental research to understand the dependence of adhesion on surface roughness. This project will develop new ways to measure roughness at small sizes, and also new ways to control it. Ultimately, the insights gained from this investigation will enable the intentional modification of roughness during manufacturing to improve the performance of the final devices. The investigation is being conducted by an international team of researchers, and incorporates specific programs for education both for engineers in industry to put the research into practice, and also for grade-school students to increase interest and participation among the next generation of American engineers. The goals of this award are: (1) to identify the length scales of surface roughness that most strongly impact adhesion; and (2) to develop fabrication strategies to rationally modify topography at these scales to control adhesion. First, the investigation will use transmission electron microscopy to characterize previously unmeasured scales of topography on technologically-relevant materials, and then use a custom micromechanical tester to measure their surface adhesion. Experimental results will be analyzed in the context of existing analytical and numerical models, in order to evaluate and then improve these models. The experiments will be complemented by large-scale computer simulations of identical surfaces, in order to gain atomic-scale information about the material response. The simulations will be carried out through a strong non-NSF-funded collaboration with the Karlsruhe Institute of Technology in Germany. Second, using advanced lithographic techniques, the small-scale roughness of test surfaces will be systematically varied and quantitatively linked to changes in properties. This will enable both experimental tests of rough-surface models, as well as the demonstration of routes to modify surface roughness to achieve an optimal surface adhesion. This investigation will have direct impact on microscale devices and on advanced manufacturing, both of which require precise understanding and control of surface properties. Further, the experimental validation of roughness models will have application to rough surfaces more broadly from automotive components to road surfaces to medical implants.