Abstract
Strong adhesion between hydrogels and various engineering surfaces has been achieved; yet, achieving fatigue-resistant hydrogel adhesion remains challenging. Here, we examine the fatigue of a specific type of hydrogel adhesion enabled by hydrogen bonds and wrinkling and show that the physical interactions–based hydrogel adhesion can resist fatigue damage. We synthesize polyacrylamide hydrogel as the adherend and poly(acrylic acid-co-acrylamide) hydrogel as the adhesive. The adherend and the adhesive interact via hydrogen bonds. We further introduce wrinkles at the interface by biaxially prestretching and then releasing the adherends and perform butt-joint tests to probe the adhesion performance. Experimental results reveal that the samples with a wrinkled interface resist fatigue damage, while the samples with a flat interface fail in ~9,000 cycles at stress levels of 70 and 63% peak stresses in static failure. The endurance limit of the wrinkled-interface samples is comparable to the peak stress of the flat-interface samples. Moreover, we find that the nearly perfectly elastic polyacrylamide hydrogel also suffers fatigue damage, which limits the fatigue life of the wrinkled-interface samples. When cohesive failure ensues, the evolutions of the elastic modulus of wrinkled-interface samples and hydrogel bulk, both in satisfactory agreements with the predictions of damage accumulation theory, are alike. We observe similar behaviors in different material systems with polyacrylamide hydrogels with different water contents. This work proves that physical interactions can be engaged in engineering fatigue-resistant adhesion between soft materials such as hydrogels.
Highlights
Hydrogels are aggregates of polymer networks and water
Hydrogels infused with mobile ions are featured as stretchable, transparent, ionic conductors that can be used for artificial muscle (Keplinger et al, 2013; Acome et al, 2018), artificial skin (Sun et al, 2014), artificial axon (Yang et al, 2015), artificial eel (Schroeder et al, 2017), touchpad (Kim et al, 2016), liquid crystal device (Yang et al, 2017), triboelectronic generator (Pu et al, 2017), and ionotronic luminescent device (Larson et al, 2016; Yang et al, 2016, 2020), a family of emerging soft devices called hydrogel ionotronics (Yang and Suo, 2018)
Under monotonic loading, the peak stress of the samples with a wrinkled interface formed at λpre = 2 is enhanced by 17.7% as compared to an enhancement of 44.9% in that of the samples with a flat interface formed at λpre = 1
Summary
Hydrogels are aggregates of polymer networks and water. The polymer network deforms and maintains shape and the water dissolves small molecules and enables their transportation. Fatigue Resistant Physical Hydrogel Adhesion the applications of hydrogel. Tough and fatigue-resistant hydrogels are synthesized based on elastic tougheners (Xiang et al, 2020). We note exceptions that fatigue-resistant hydrogel adhesion can be achieved based on physical interactions. We find that the nearly perfectly elastic polyacrylamide hydrogel suffers fatigue damage under the same experimental protocol and that its S-N curve is comparable to that of the interfacial fatigue in the wrinkled-interface samples prepared at λpre = 2, implying that the physical interaction–based interface can be as strong as the bulk of the covalently crosslinked hydrogel. The presented observations suggest that fatigue-resistant adhesion between soft and wet materials such as hydrogels can be engineered based on physical interactions. The sample was stored in an oven at 65◦C for 4 h, followed by 12 h of exposure to the open air for thorough desiccation
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