Flaw Sensitivity and Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels

Abstract

Tensile fatigue behavior is commonly overlooked as researchers pursue the toughest hydrogels. This work describes a poly(vinyl alcohol) (PVA) hydrogel prepared through freezing–thawing (FT) processing to achieve varied monotonic strength and toughness. The monotonic tensile responses of relatively strong and weak versions of the hydrogel are studied with cylindrical hole and crack‐like flaws of different sizes to develop an understanding of monotonic strength in the presence of two different, extreme defect types. The monotonic strength of the samples with cylindrical defects is reasonably predicted using nominal stress which accounts for a loss of load‐bearing area, while linear‐elastic fracture mechanics gives a first‐order approximation of the impact of crack‐like flaw size on monotonic strength. A subset of key defected samples are further subjected to cyclic loading and fatigue failure at varying stress amplitude. The cylindrical defect samples outperformed cracked samples in fatigue, and the utilization of four FT cycles instead of two improved both monotonic toughness and fatigue properties. This work represents the first tensile fatigue analysis on defected hydrogel materials, sheds light on the behavior of hydrogels in cyclic loading environments, and evaluates both the monotonic toughness and fatigue behavior of soft materials with and without defects.

All-round supramolecular zwitterionic hydrogel electrolytes enabling environmentally adaptive dendrite-free aqueous zinc ion capacitors

“…As shown in Fig. S13 and S14 (ESI†), the CP/EGZn/betaine hydrogel electrolytes not only retained excellent mechanical properties under these demanding conditions, their qualitative behaviour is comparable to that of most existing PAAm gels, 50 alginate gels, 51 and PVA gels, 52,53 as well as DN gels 49 and zwitterion gels, 54 especially in terms of the fracture energy (Fig. S14, ESI†) and toughness (Fig.…”

“…It was found that the CP/EGZn/betaine hydrogel electrolyte with 0.6% CNF performed better in terms of tensile strength (70.3 kPa), Young's modulus (5.7 kPa), and toughness (61.6 kJ m À3 ) than that of P/EGZn/betaine hydrogel electrolyte, which is attributed to the reinforcement of the rigid CNF, bridging the PAA chains and the supramolecular betaine chains via H-bonds 2a and b show the stretching and compression process as well as the puncture resistance of the CP/EGZn/betaine hydrogels, respectively. (c) Comparison between this work and previous DN gels, 49 PAAm gels, 50 alginate gels, 51 PVA gels, 52,53 and zwitterion gels 54 in terms of fracture energy (Fig. S14, ESI †) and toughness.…”

“…The insets in Fig.2a and bshow the stretching and compression process as well as the puncture resistance of the CP/EGZn/betaine hydrogels, respectively. (c) Comparison between this work and previous DN gels,49 PAAm gels,50 alginate gels,51 PVA gels,52,53 and zwitterion gels54 in terms of fracture energy (Fig.S14, ESI †) and toughness. (d) Top: Photographs demonstrating the inflation process of the CP/EGZn/betaine hydrogel, where the specimen is initially sealed on the inflation port (port diameter of 0.5 cm) of an air pump and then inflated into a large balloon.…”

A versatile hydrogel network–repairing strategy achieved by the covalent-like hydrogen bond interaction

“…( F ) A mechanical properties space for soft materials; the two axes represent the fracture energy Г and the work to rupture W * , respectively, and the dashed line represents the fractocohesive length Г/ W * . The trehalose-modified PAAm hydrogels are compared with PAAm hydrogels, DN hydrogels ( 2 ), alginate hydrogels ( 55 ), PVA hydrogels ( 56 ), skin ( 57 ), natural rubbers ( 58 ), and polyurethane ( 46 ). ( G ) Trehalose-modified hydrogels with the edge cut are highly stretchable and exhibit flaw-tolerant capability.…”

Physical modification approaches to enhance cell supporting potential of poly (vinyl alcohol)‐based hydrogels

“…Chemical cross‐linking may occur through various processes such as free‐radical polymerization, chemical agents and enzymatic reactions and high energy irradiation, which normally form covalent bridges between PVA polymer chains 3 . The crystalline nature of PVA is also of interest for forming crystalline zones as physical cross‐links network in a hydrogel, which can be developed by repeated simple freeze–thaw cycles 4 . In fact, such formed crystallites, that act as holding points within the network skeleton, distribute mechanical loads into gel structure and enhance its load‐bearing potential 5 …”