GOALI: A Multiscale Approach on Interfacial and Structural Interlocking Between Polymer Grafted Shape Memory Pillars

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TECHNICAL SUMMARY:The award is based on complementary research activities, including polymer synthesis, fabrication and characterization in Yang's lab in Materials Science and Engineering (MSE) at the University of Pennsylvania (Penn), theoretical modeling at the molecular and meta-structural (ordered array) levels in Li's lab at Penn/MSE, in collaboration with Xie's lab at General Motors Global Research & Development Center (GM). It builds upon their knowledge in shape memory polymer (SMP) chemistry and surface chemistry toward robust and industrial scale adhesion. The focus of this proposal is on the fundamentally unresolved question concerning the individual and combined roles of surface chemistry, topography, and compliance on adhesion at different length scales. Specifically, the PIs plan to: (1) fabricate SMP pillar arrays with precise control over size, aspect ratio, and spacing; (2) graft well-controlled polymer brushes to manipulate molecular interactions (e.g. H-bonding and ion-pi interactions) for both bonding and debonding; (3) systematically study adhesion and peeling off on complementary SMP pillars under deformation and recovery, and (4) compare experimental results with multiscale modeling throughout each relevant lengthscale and develop a complete mechanistic view of interlocking dry adhesion. NON-TECHNICAL SUMMARY:Adhesion between polymers plays an important role in a wide range of industrial applications. Liquid based adhesives offer strong adhesion, however their thermal curing is energy intensive and the adhesion is generally not reversible. Nature provides us with remarkable examples of reversible dry adhesion as manifested in burdock seeds and gecko foot hairs, where no liquid or lengthy curing is involved in the adhesive attachment. This proposal seeks to develop biomimetic superglue-like, yet reworkable, dry adhesives. It will not only provide important scientific insights, but also impact a wide range of technologies, including electronic packaging, automotive and airplane assemblies, and soft robotics. Students at all levels will be exposed to a diverse range of topics in chemistry, materials science and engineering, soft mechanics, nanofabrication and computational modeling through new training and outreach opportunities, including summer lectures by the industrial researcher from General Motors, integration of the research outcome in courses, engagement of high school and undergraduate students through summer research and senior design projects, and industrial internship by a PhD student at General Motors Global R&D Center. The research outcome will also create a significant opportunity to excite the general public, thereby engaging their interest in Science, Technology, Engineering, and Mathematics (STEM).