Overcoming the adhesion paradox and switchability conflict on rough surfaces with shape-memory polymers

Abstract

Smart adhesives that can be applied and removed on demand play an important role in modern life and manufacturing. However, current smart adhesives made of elastomers suffer from the long-standing challenges of the adhesion paradox (rapid decrease in adhesion strength on rough surfaces despite adhesive molecular interactions) and the switchability conflict (trade-off between adhesion strength and easy detachment). Here, we report the use of shape-memory polymers (SMPs) to overcome the adhesion paradox and switchability conflict on rough surfaces. Utilizing the rubbery–glassy phase transition in SMPs, we demonstrate, through mechanical testing and mechanics modeling, that the conformal contact in the rubbery state followed by the shape-locking effect in the glassy state results in the so-called rubber-to-glass (R2G) adhesion (defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state), with extraordinary adhesion strength (>1 MPa) proportional to the true surface area of a rough surface, overcoming the classic adhesion paradox. Furthermore, upon transitioning back to the rubbery state, the SMP adhesives can detach easily due to the shape-memory effect, leading to a simultaneous improvement in adhesion switchability (up to 10 3 , defined as the ratio of the SMP R2G adhesion to its rubbery-state adhesion) as the surface roughness increases. The working principle and the mechanics model of R2G adhesion provide guidelines for developing stronger and more switchable adhesives adaptable to rough surfaces, thereby enhancing the capabilities of smart adhesives, and impacting various fields such as adhesive grippers and climbing robots.

Triple-Bioinspired Shape Memory Microcavities with Strong and Switchable Adhesion

“…This reversion also leads to the return of the surface’s adhesion to both solid and liquid to a low adhesion state. The above results indicate that based on the SME of our surface, switchable adhesion to both solid and water can be achieved, which is more advanced than those SMP surfaces that can display tunable adhesion to a single solid or water. ,,, …”

“…The above results indicate that based on the SME of our surface, switchable adhesion to both solid and water can be achieved, which is more advanced than those SMP surfaces that can display tunable adhesion to a single solid or water. 30,31,35,36 As mentioned earlier, the variation of adhesion behavior toward solid and liquid is primarily because of changes in microstructure and roughness. The effects of surface microstructure and roughness on adhesion properties were analyzed using laser scanning confocal microscopy.…”

“…The suction cup inspired hole-shaped SMP microstructure (H-SMPM) was prepared by replicating the reverse structure of silicon template arrays with SMP (Figure b). Similar to the mucus found in creepers, SMPs can transition between rubbery and glassy states in response to external stimuli, such as temperature and light, resulting in significant changes in modulus. − The modulus ( E ) of the SMP used in this work switches between about 1027 MPa (glassy state) and 1 MPa (rubbery state), as the temperature switches between 25 and 90 °C, respectively. The H-SMPM surface exhibits high adhesion to the solid after a two-step process.…”

Skin‐customized wearable device adhesive without skin damage

“…As the skin surface became rougher, the contact area between the PDMS pad and the skin surface decreased, and a decreasing tendency for the adhesive strength of the PDMS pad was observed owing to incomplete interface contact. 26 In addition, it is notable that in the case of skin surface with relatively highroughness values, such as the chest of a pig and the back of a pig, the adhesive strength of the hole pattern is superior, while in the case of skin with lower roughness values, such as the back of a fish and the back of a crab, the adhesive strength of the cylinder pattern is superior. This is because the hole pattern has the advantage of having a large contact area with the rough skin surface.…”

Switchable Adhesive Based on Shape Memory Polymer with Micropillars of Different Heights for Laser-Driven Noncontact Transfer Printing

“…Good attempts are to exploit the rapid local surface deformation from the evaporation of an absorbing layer, − the interfacial thermal mismatch, − the snap-through behavior of a buckled film, , or the microcavity pressure change. − Here, we report a simple yet robust design of switchable adhesive based on a thermal responsive SMP with micropillars of different heights for laser-driven noncontact transfer printing. This switchable adhesive takes advantage of the ultrastrong adhesion state of SMP by maximizing the contact area due to the high adaptation property − at a temperature above the glass transition temperature, ultralarge adhesion switch to the desired weak adhesion state by minimizing the contact area from the various levels of shape recovery of micropillars in a rapid manner. Benefiting from the extraordinary adhesion switchability of SMP adhesive with micropillars of different heights, a promising laser-driven noncontact transfer printing toward high yields and efficiency in a programmable way can be easily achieved by utilizing a highly localized laser heating system.…”