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Many living tissues, such as muscle, become mechanically stronger with growth. Yet, synthetic hydrogels usually exhibit an opposite size‐mechanical property relation, that is, swelling‐weakening behavior. Herein, a series of swollen yet strengthened polyampholyte (PA) hydrogels are developed via a simple metal‐ion solution soaking strategy. In this strategy, a dynamic PA hydrogel (with ionic bonds) is dialyzed in ZrOCl2 solutions (Step‐I) and deionized water (Step‐II) successively to obtain equilibrated hydrogels. Due to the specific Zr4+ ions and PA network structure, Step‐I takes several months with sample size and mechanical performance increasing continuously, while Step‐II only needs several days. Through this strategy, the resultant hydrogel networks are reorganized and eventually constructed by ionic and metalligand bonds, enabling the swelling yet strengthening behavior. A systematic study confirms that dialysis time in Step‐I and corresponding ZrOCl2 concentration can significantly affect the multiphase microstructures of the hydrogels, resulting in different mechanical enhancements. The optimized hydrogel possesses 39.2 MPa of Young's modulus and 3.7 MPa of tensile strength, which are 302 and 5.5 times these of the original PA gel, respectively. Despite distinct swelling, these hydrogels still mechanically surpass many existing high‐performance hydrogels. This study opens a novel pathway for fabricating swollen yet strengthened hydrogels. [ABSTRACT FROM AUTHOR]

The poor adhesion performance of typical gels still remains a challenge to find a simple method to achieve strong and reversible adhesion with the existence of water. Here, a poly(acryloyloxyethyl trimethyl ammonium chloride‐co‐2‐vinyl‐4‐6‐diamino‐1,3,5‐triazine) (P(DAC‐co‐VDT)) gel with high and adjustable interfacial adhesion is fabricated by combining cation‐triazine π interaction and multiple hydrogen bonding and through a one‐pot route. Characterization of the gels reveals that the two types of interactions are introduced into the gel network and that the gel–gel and gel–glass interfacial adhesion can be readily adjusted in a wide range from 15.98 to 123.60 kPa. This approach enables the creation of high‐strength composites using P(DAC‐co‐VDT) gel as matrix, anionic monomer sodium p‐styrene sulfonate as ion concentration adjustor, and discrete quartz sands as filler with easy and repeated moldability and self‐healing capability. [ABSTRACT FROM AUTHOR]

The amount of winter precipitation over southeast China (SCWP) is significantly affected by the El Niño–Southern Oscillation (ENSO), with generally an enhanced SCWP response to El Niño events. In this paper, we find that this relationship shows remarkable nonstationarities on the multidecadal timescale. Running ENSO–SCWP correlation maintains statistically significant before the mid‐1960s and after the mid‐1990s but not during the interim period, which exhibits an approximate synchronized temporal evolution with the Atlantic Multidecadal Oscillation (AMO). A statistical method for interpreting nonstationary relationships is then applied to quantitatively verify and measure this possible AMO modulation. It is demonstrated that the nonstationary ENSO–SCWP correlation can be expressed to a large extent by the influence of the AMO–ENSO nonlinear effect (AMO*Niño3.4) on the SCWP. This influence intensifies the ENSO–SCWP relationship during the positive AMO phase but weakens it during the negative AMO phase. Therefore, the nonstationarity in the ENSO–SCWP relationship comes predominantly from an AMO modulation via this key nonlinear effect. We further suggest that a positive AMO favours a westward shift of ENSO sea surface temperature (SST) anomaly pattern in the tropical Pacific. Correspondingly, the anomalous western North Pacific (WNP) anticyclone also migrates westward, which gives rise to pronounced moisture transports and vertical motions over the adjacent southeast China, thereby resulting in a significant ENSO–SCWP relationship. In contrast, during the negative AMO phase, the eastward‐shifted ENSO SST and WNP anticyclonic anomalies produce significant atmospheric anomalies primarily to the east of the Chinese mainland, thus having less effect on the SCWP. [ABSTRACT FROM AUTHOR]

Despite existing in biological systems, developing synthetic polyampholyte (PA) hydrogels constructed by both ionic and metal–ligand bonds remains challenging. Herein, a simple secondary equilibrium approach is proposed to fabricate strong and tough PA hydrogels via the synergy of ionic and metal–ligand bonds. The original PA gels (constructed by ionic bonds) are first dialyzed in multivalent metal‐ion solutions to reach a swelling equilibrium and then moved to deionized water to dialyze excess free ions to achieve a new equilibrium. Through this approach, the original PA gel network can be optimized and eventually constructed by ionic and metal–ligand bonds, enabling a synergistic reinforcement. By selecting different original PA gel systems and diverse multivalent metal‐ions, the proposed approach is proved to be generalizable to fabricate strong and tough PA gels. Additionally, the hydrogels have stable ion‐conductivity even at the water‐equilibrium state, making them promising as strain sensors. The viscoelastic and elastic contributions to the mechanical properties of the hydrogels by a viscoelastic model are also discussed to further understand the strengthening and toughening mechanisms. The proposed strategy is simple but effective for achieving strong and tough PA‐based hydrogels. This study also provides new insights for PA hydrogels in electrolyte environments. [ABSTRACT FROM AUTHOR]

Rewritable information record materials usually demand not only reversibly stimuli‐responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super‐strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion‐hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22 MPa, work of tension of 12.8 MJ m−3, and modulus of elasticity of 8.6 MPa. Moreover, the SP‐based Ca2+ crosslinked hydrogels can be enhanced further when exposed to UV‐light via ionic interaction coordination between Ca2+, merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices. [ABSTRACT FROM AUTHOR]

Two novel furfurylamine type benzoxazine prepolymers are firstly synthesized from 4,4′‐bishydroxydeoxybenzoin (BHDB) and 4,4′‐dihydroxybenzophenone (DHBP). Both BHDB‐ and DHBP‐based polybenzoxazines present accelerated curing behaviors, high glass transition temperatures, and very low heat release capacity values, resulting from the introduction of electron‐withdrawing groups and furan rings. It is especially noteworthy that the flame retardancy of DHBP‐based polybenzoxazine is classified as UL‐94 V‐1 grade, whereas that of BHDB‐based polybenzoxazine is evaluated to be UL‐94 V‐2 grade. Hence, DHBP is considered as an alternative to BHDB for benzoxazine preparation because of its similar chemical structure, competitive price, high efficiency preparation, and outstanding flame resistance. Therefore, this work not only provides an economical and effective strategy for the preparation of halogen‐free, phosphorus‐free, and intrinsically flame‐retardant benzoxazine resins but also provides important insight into the effects of electron‐withdrawing bridge groups on the curing behavior and thermal and flame‐retardant properties of benzoxazine resins. [ABSTRACT FROM AUTHOR]

In order to improve the performance of inorganic/organic composites, aluminum trihydroxide (ATH) core composites with a styrene‐ethylene‐butadiene‐styrene block copolymer grafted with maleic anhydride (MAH‐g‐SEBS) shell phase, and P‐N flame retardant as a synergistic agent, were prepared through an interface design. The effects of polyethylene glycol (PEG) content on the interfacial interaction, flame retardancy, thermal properties, and mechanical properties of high‐density polyethylene (HDPE)/ATH composites were investigated by small angle X‐ray diffraction, rotational rheometer, limiting oxygen index, thermogravimetric analysis (TGA), and tensile testing. The ATH synergistic effects of P‐N flame‐retardant improved the combustion performance of HDPE/ATH/PEG(3%)/MAH‐g‐SEBS/P‐N (abbreviated as HDPE/MH3/M‐g‐S/P‐N) composite by forming more carbon layer, increased the elongation at break from 21% to 558% compared to HDPE/ATH, and increased the interface thickness from 0.447 to 0.891 nm. SEM results support the compatibility of ATH with HDPE increased and the interfacial effect was enhanced. TGA showed the maximum decomposition temperature of the two stages and the yield of the residue at high temperature increased first and then decreased with the increase of PEG content. Rheological behavior showed the storage modulus, complex viscosity, and the relaxation time initially increased and then decreased with the increase of PEG content indicating PEG, M‐g‐S, and ATH powder gradually formed a partial coating, then a full coating, and finally an over‐coated core‐shell structured model. [ABSTRACT FROM AUTHOR]

The research on multiple hydrogen bonds (H‐bonds) hydrogels have gradually aroused wide interest. In this paper, a multiple H‐bonds‐reinforced poly(acrylamide‐co‐2‐vinyl‐4,6‐diamino‐2‐vinyl‐1,3,5‐triazine)/tannic acid (P(Am‐co‐VDT)/TA) hydrogels are prepared. The results suggest that the prepared hydrogel has two types of H‐bonds crosslinking regions: A "soft" region of H‐bonds between the diaminotriazine (DAT) moieties on the polymer chains and the TA pyrogallol/catechol groups, and a "hard" region of H‐bonds forming by DAT moieties with itself. The hard crosslinking region exhibits significantly higher activation energy than the soft region. Such soft and hard dual physically crosslinked networks dramatically enhance the mechanical properties of P(Am‐co‐VDT)/TA hydrogels in a synergistic manner (tensile strength is 2.34 MPa, elongation at break is 410%). Due to the multiple hydrogen bonds, the hydrogel has good pH sensitivity and rapid response to shape memory within a few minutes. In addition, the hydrogels have the capacity of physical adsorption of the anti‐inflammatory drug diclofenac sodium and other molecules with a specific spatially arranged chemical composition. These hydrogels with high mechanical strength, excellent shape memory behavior, and capacity of adsorption of anti‐inflammatory drug could be attractive candidates for applications in the fields of biomedicine, tissue engineering, and medical materials. [ABSTRACT FROM AUTHOR]

A versatile ionic crosslink lithography (ICL) approach is reported to achieve geometry transitions of strong polyvinyl alcohol/sodium alginate (PVA/SA) hydrogels in a controllable and programmable manner. Specifically, localized PVA/SA and PVA/SA/Fe3+ hydrogel domains of significantly different swellabilities (i.e., in‐plane gradient) are created by patterning and selective ionic crosslinking of one single type of PVA/SA hydrogel. A simple two‐step sequential pre‐ and free‐swelling, or each alone, directs the patterned, inhomogeneous hydrogel to transform in various programmable and quasi‐quantitative ways through local bulging and/or global buckling. All types of shape changing are reversible and repeatable due to the reversible nature of ionic coordination in the hydrogel networks. The flexibility and versatility of 3D printing is also demonstrated in creating through‐thickness gradient in PVA and PVA/SA hydrogel assemblies with similar morphing capability. The ICL approach developed in this work may help shed some light on developing strong and shape morphing hydrogels as soft sensors and actuators and for potentially biomimetic transformations. The ICL approach may also be transferable to fabrication of many other types of hydrogel materials for similar applications. [ABSTRACT FROM AUTHOR]

The adhesion strength and water resistance of stainless steel and adhesive resin composites determine the long‐term performance of wires and cables; however, adhesion at stainless steel interfaces is difficult. Herein, we prepared ethylene acrylic acid/linear low‐density polyethylene (EAA/LLDPE) blends with good mechanical and adhesive properties. Silane was anchored to the surface of stainless steel. The effects of silane functionalization on the adhesion surface were investigated by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The reaction mechanism between the stainless steel, silane, and EAA/LLDPE revealed adhesion was optimized when a 3:7 volume ratio of 3‐methacryloxypropyltrimethoxysilane (MEMO): 3‐aminopropyltrimethoxysilane (A‐1110) was used to modify the stainless steel substrate. SEM images of EAA/LLDPE film peel surfaces found the silane‐treated stainless steel substrates produced rough surfaces with a uniform void indicating the silane treatment enhanced the stainless steel and EAA/LLDPE film interaction. The stainless steel and EAA/LLDPE film adhesion and water resistance improved and the peel strength after water resistance testing at 68°C for 168 h increased from 3.18 N/cm to 9.37 N/cm compared to untreated stainless steel. Silane‐modified stainless steel and EAA/LLDPE blend film composite materials demonstrate potential for application in wires and cables used in environmental corrosion‐resistant applications. POLYM. ENG. SCI., 59:1866–1873, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Tough hydrogels have shown strong potential as structural biomaterials. These hydrogels alone, however, possess limited mechanical properties (such as low modulus) when compared to some load-bearing tissues, e.g., ligaments and tendons. Developing both strong and tough soft materials is still a challenge. To overcome this obstacle, a new material design strategy has been recently introduced by combining tough hydrogels with woven fiber fabric to create fiber reinforced soft composites (FRSCs). The new FRSCs exhibit extremely high toughness and tensile properties, far superior to those of the neat components, indicating a synergistic effect. Here, focus is on understanding the role of energy dissipation of the soft matrix in the synergistic toughening of FRSCs. By selecting a range of soft matrix materials, from tough hydrogels to weak hydrogels and even a commercially available elastomer, the toughness of the matrix is determined to play a critical role in achieving extremely tough FRSCs. This work provides a good guide toward the universal design of soft composites with extraordinary fracture resistance capacity. [ABSTRACT FROM AUTHOR]

A simple, multiple‐hydrogen‐bond approach to fabricating physically crosslinked, Amylopectin reinforced polyacrylamide/poly(vinyl alcohol) (Amy/PAAm/PVA) double‐network (DN) hydrogels with super toughness in bulk and at solid interfaces is reported. The Amy/PAAm/PVA DN hydrogels exhibit high tensile strength (854.1 kPa), high extensibility (≈eight times), high bulk toughness (4094.8 kJ m−3), good self‐recovery property (≈92% of self‐recovery at room temperature), and strong adhesion to nonporous glass surfaces (≈158 kPa). Such tough and adhesive DN hydrogels have great potential for various applications in engineering artificial soft tissues, flexible electronics, and wearable devices. [ABSTRACT FROM AUTHOR]