Collaborative Research: Deformation-Dependent Adhesion of Stretched Compliant Networked Polymer Systems

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This grant will focus on developing a fundamental understanding of how changing the shape of soft, adhesive materials -- for example, through stretching or compression -- modifies their adhesive properties. Modern theories of adhesion were originally developed to describe contact with relatively stiff materials like rubber, but much softer sticky materials are ubiquitous in biology, medicine, engineering, and everyday consumer products. Over the past decade, soft solid surface mechanics has emerged as an exciting new field of study, driven largely by the surprising discovery that classic theories fail to describe the contact behavior of compliant materials and that soft materials adhere very differently than their stiffer counterparts. Recent experiments, theory, and simulations have revealed a rich array of new physics and suggest a powerful new design space for engineering applications. The fundamental discoveries and materials developed through this research project will enable the development of new strain-controlled, responsive adhesives and will also involve student researchers at various stages of their educational careers from undergraduates to postdoctoral scholars. An “Adhesion Engineering Summer Camp” will be established to bring Williams College students to visit Purdue University each summer of the project.The surface properties of compliant polymers have been shown to change as a function of bulk deformation in previously-unanticipated ways. While recent debates over the nature of strain-dependent surface stress in soft solids have motivated numerous experimental and theoretical studies, much less work has focused on strain-dependent adhesion. By performing measurements that directly investigate the normal adhesive response of compliant network polymer systems as a function of both quasi-static and dynamic deformation using integrated mechanical testing and direct imaging, this project will establish a fundamental understanding of how the adhesion of soft materials is modified by deformation across a broad range of length scales, time scales, and material properties. The interplay between strain, adhesion energy, network architecture, and material relaxation mechanisms will be investigated through the experimental, numerical, and theoretical work in this collaborative grant. The specific research objectives of the project will be to (i) quantify quasistatic adhesion to stretched, compliant network polymer systems across length scales and (ii) characterize the adhesive response of compliant networked polymer systems during dynamic deformation.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.