Controlling adhesion on demand is essential for many manufacturing and assembly processes such as microtransfer printing. Among various strategies, pneumatics‐controlled switchable adhesion is efficient and robust but currently still suffers from challenges in miniaturization and high energy cost. In this paper, a novel way to achieve tunable adhesion using low pressure by inducing sidewall buckling in soft hollow pillars (SHPs) is introduced. It is shown that the dry adhesion of these SHPs can be changed by more than two orders of magnitude (up to 151×) using low activating pressure (≈−10 or ≈20 kPa). Large enough negative pressure triggers sidewall buckling while positive pressure induces sidewall bulging, both of which can significantly change stress distribution at the bottom surface to facilitate crack initiation and reduce adhesion therein. It is shown that a single SHP can be activated by a micropump to manipulate various lightweight objects with different curvatures and surface textures. Here, it is also demonstrated that an array of SHPs can realize selective pick‐and‐place of an array of objects. These demonstrations illustrate the robustness, simplicity, and versatility of these SHPs with highly tunable dry adhesion.
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Free, publicly-accessible full text available May 1, 2025
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Free, publicly-accessible full text available March 1, 2025
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Herein, a new class of robust bicontinuous elastomer–metal foam composites with highly tunable mechanical stiffness is proposed, fabricated, characterized, and demonstrated. The smart composite is a bicontinuous network of two foams, one metallic made of a low melting point alloy (LMPA) and the other elastomeric made of polydimethylsiloxane (PDMS). The stiffness of the composite can be tuned by inducing phase changes in its LMPA component. Below the melting point of the LMPA, Young's modulus of the smart composites is ≈1 GPa, whereas above the melting point of the LMPA it is ≈1 MPa. Thus, a sharp stiffness change of ≈1000× can be realized through the proposed bicontinuous foam composite structure, which is higher than all available robust smart composites. Effective medium theory is also used to predict the Young's modulus of the bicontinuous smart composites, which generates reasonable agreement with experimentally measured Young's modulus of the smart composites. Finally, the use of these smart materials as a smart joint in a robotic arm is also demonstrated.
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Robust Three‐Component Elastomer–Particle–Fiber Composites with Tunable Properties for Soft Roboticsmore » « less
Materials with tunable properties, especially dynamically tunable stiffness, have been of great interest for the field of soft robotics. Herein, a novel design concept of robust three‐component elastomer–particle–fiber composite system with tunable mechanical stiffness and electrical conductivity is introduced. These smart materials are capable of changing their mechanical stiffness rapidly and reversibly when powered with electrical current. One implementation of the composite system demonstrated here is composed of a polydimethylsiloxane (PDMS) matrix, Field's metal (FM) particles, and nickel‐coated carbon fibers (NCCF). It is demonstrated that the mechanical stiffness and the electrical conductivity of the composite are highly tunable and dependent on the volume fraction of the three components and the temperature, and can be reasonably estimated using effective medium theory. Due to its superior electrical conductivity, Joule heating can be used as the activation mechanism to realize ≈20× mechanical stiffness changes in seconds. The performance of the composites is thermally and mechanically robust. The shape memory effect of these composites is also demonstrated. The combination of tunable mechanical and electrical properties makes these composites promising candidates for sensing and actuation applications for soft robotics.
