Programmable adhesion in dry and wet environments through geometric design

Abstract

Strong and reversible adhesives are needed for diverse applications including manufacturing, robotics, packaging, wearable electronics, and wound management. To enable switchable adhesion, adhesives require to achieve high capacity of resisting crack propagation while allowing promotion of the crack propagation for easy release. Difficulty of achieving switchable adhesion is further amplified in wet environment. Achieving adhesion itself is inherently difficult underwater due to the presence of water molecules at the interface, which significantly reduces the effectiveness of interaction forces like Van der Waals forces. Chemical modifications are often adopted to tune the adhesion energy of adhesive, but it has limitation in controllable adhesion. Here, we introduce strategies for strong yet easy release adhesives through art-inspiration (Kirigami) and bio-inspiration (Cephalopod). Chapter 2 explores the mechanical aspects of adhesive peeling. We compare experimental data with theoretical models to discuss the effect of energy dissipation, particularly through the plastic work of the adherend. Chapter 3 introduces kirigami-inspired metamaterial adhesives which utilize nonlinear cuts in adhesives to suppress crack propagation by forcing cracks to reverse direction with low local peel angle (∼ 10°) for ×60 enhancement in adhesion, while promoting crack growth in the opposite direction for easy release and reusability. Furthermore, secondary cut in the primary cut enables additional tunability of adhesive force capacity and energy of separation by steering cracks in multiple directions resulting in increasing work of separation by ×1.5 while maintaining the peel force. Chapter 4 introduces bio-inspired adhesives which draw inspiration from the infundibulum structure of an octopus. We design a compliant, curved stalk paired with an active, deformable membrane that adapts its shape to complex surface conditions for effective attachment. The curvature of the stalk enhances attachment by increasing conformal contact on large-scale curvatures and improving contact stress around the stalk's perimeter, which allows it to better adapt to small-scale roughness. This enables switching ratios up to ×1000 from the activated to the deactivated state. The attachment strength is consistently high (∼ 60 kPa) across various conditions, including substrate material, substrate curvature and roughness, testing fluid type, and testing fluid viscosity. Chapter 5 investigates the effect of surface chemistry on the attachment of the octopus-inspired adhesive underwater. The surface of the active membrane is chemically modified with diverse chemicals to tune its intrinsic adhesion energy and hydrophilicity. The impact of these modifications on underwater attachment is systematically analyzed. Chapter 6 summarizes the key discussions, contributions, and potential future directions of this research.