RUI: The Origins of Statistical Variation of Strength in Micropatterned Adhesive Contacts

The University Corporation, Northridge, Northridge CA

Investigators

Abstract

This grant investigates the relationship between the properties of roughness on real-world surfaces and the resulting performance of novel controllable and reusable adhesive surfaces. Based upon patterning surfaces with arrays of microscale structures, taking inspiration from the toepads of insects and lizards, these adhesives can transition between strong attachment and easy detachment over many repeat cycles. This may enable new capabilities in gripping of delicate objects in extreme environments (e.g. in vacuum and underwater) or in the creation of multifunctional interfaces (e.g. in biomedical diagnostics and therapeutics). Differences in interfacial defects at each micropatterned sub-contact results in variation in local adhesive performance, with the statistical properties influencing the global strength and stability of the adhesive patch. This work will establish relationships which enable prediction of the emerging statistical behavior and resulting adhesive performance, based upon characteristic properties of the contacting surfaces. This grant will also strengthen research-based educational activities for the Mechanical Engineering student body at California State University Northridge, of whom 65.6 percent are from traditionally underserved minorities. The reach will be extended through a course-based undergraduate project, allowing a large volume of students to contribute meaningful data toward achieving the research objectives. Additionally, participating students will serve as undergraduate mentors and run high school outreach workshops themed around the topic. Several key gaps in understanding will be addressed in this study. The adhesive strength of sub-contacts has only been characterized for idealized defects, and a comprehensive range of defect size, shape, and position will be considered. Cohesive zone finite element simulations of microstructural detachment will provide the strength as defect properties are varied. Defect formation on rough surfaces is not understood, and must be examined to relate the surface characteristics to the statistical distribution of adhesive strength. Molecular dynamics simulations will yield contact maps as spectral properties of the roughness and the elastic properties of the bodies are varied. Experimental characterization of micropatterned adhesives will be performed on surfaces with manufactured defects and random roughness to validate relationships obtained through modeling and simulation. Lastly, understanding of the influence of statistical variation in sub-contact adhesive strength on performance at length and time scales approximating temporary bonding applications must be expanded. A semi-analytical mechanical model of adhesive patch behavior will integrate this local variation and examine the combined effects of substrate curvature, loading rate, and patch size on the global adhesive performance. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.