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Abstract: A series of novel graphene oxide (GO)/poly(acrylic acid-co-acrylamide) super-absorbent hydrogel nanocomposites were prepared by in situ radical solution polymerization. The effects of GO content on the chemical structure, morphology and miscibility of the hydrogels were studied. The swelling behaviors, swelling kinetics and pH-responsive behaviors of the hydrogels were also evaluated. Owing to the hydrogen bonds and possible covalent bonds between GO and polymer chains, relatively lower content (<0.30wt%) of GO could be dispersed well in the polymer matrix and enhanced the intermolecular interactions between the components effectively. On the contrary, an excessive amount of GO might form large agglomerates and weakened the interfacial interactions, resulting in the micro-phase separation between the components. Furthermore, the swelling capacities and swelling rates of hydrogels went up with increasing GO loadings to 0.30wt% and then decreased with further increasing GO loadings. It is worth noting that the hydrogel only containing 0.10wt% GO exhibited significant improvement of swelling capacity in neutral medium, and could also retain relatively higher swelling capacities to a certain degree at acidic and basic solutions. Therefore, the as-prepared GO-based super-absorbent hydrogels might have potential applications in many areas, such as biomedical engineering, construction engineering and hygienic products. [Copyright &y& Elsevier]

Abstract: The effects of filler-matrix morphology on mechanical behaviour of thermo-moulded films based on native or amorphous corn starch as matrix, and zein (sizes of <100, <250, and >500μm) as filler were investigated. The morphology and mechanical behaviour were characterized by Confocal Light Scanning Microscopy and three point bending test, respectively. For native starch blends, the zein network was relatively dense when initial zein size increased from 100 to 500μm. However, small initial zein size favored continuous morphology for amorphous starch blends. It is noted that the stress at rupture values of native starch blends decreased when zein size increased, indicating relatively compact zein network damaged the stress of starch matrix. On the contrary, the variations of the stress at rupture values of amorphous starch blends were not significantly different, attributing to the heterogeneous morphology of incomplete zein network dispersed in the amorphous starch matrix. [ABSTRACT FROM AUTHOR]

Chitosan (CS), a linear natural polysaccharide, is often chosen to prepare hydrogels due to its hydrophilic nature and biocompatible merits. However, mechanically weak CS-based hydrogels show limited applications. Herein, we show a new multi-structural network design for mechanically enhancing graphene oxide (GO) filled CS-based hydrogel nanocomposites. The designed multi-structural hydrogel network shows a relatively dense structure with surrounding polymer chains at the local zone of self-assembled GO-CS units and a relatively loose structure at the far zone, resulting in the mechanical enhancement. By tuning GO loading and molecular weight of CS in a specific range, we intend to understand the effect of the specific multiple network structures on the mechanical properties of the composites. The experimental results demonstrate that the multi-structural network design provides an effective reinforcement mechanism for the hydrogel composites. The composite (containing only 0.30 wt% GO and ≈90 wt% water) has achieved 163% and 91% increases in compressive strength and work of compression, respectively, comparing to those of the neat gel. The findings may be generally applicable for the structural design and understanding of nanofiller-reinforced hydrogel and elastomer composites. [ABSTRACT FROM AUTHOR]

Thermoresponsive hydrogel-based actuators have shown great potential in tissue engineering, biosensors and soft robots, while the preparation of temperature-driven bilayer hydrogel actuators with rapid responseness and recovery properties remains a challenge. Inspired by the layered heterostructure of human skin, we developed a Janus bilayer structure actuator consisting of thermoresponsive double network (TDN) hydrogel and polydimethylsiloxane (PDMS) elastomer with tough interface adhesion. Specifically, PNaAMPS/P(NIPAM- co -AAm) TDN hydrogel via photocopolymerization of N-isopropyl acrylamide (NIPAM) and acrylamide (AAm) and reinforced by microgel poly(2-acrylamide-2-methylpropane sulfonate sodium salt) (PNaAMPS) was in situ grafted onto benzophenone-activated PDMS surface, exhibiting strong interface adhesion (628 Jm-2 adhesion energy). The thermoresponsive shape deformations of the double-layer structure actuator were controllable by adjusting hydrogel/elastomer thickness ratio and introduction of metal ions, taking advantage of the different swelling and shrinkage characteristics of the hydrogel layer and the elastomer layer. The TDN/PDMS bilayer structure actuator, which integrates the "Janus" structure, thermal responsiveness and photothermal conversion, provides new ideas for the application and remote control of soft robots and soft actuators. [Display omitted] • Thermoresponsive bilayer actuator composed of hydrophilic TDN hydrogel and hydrophobic PDMS elastomer. • The bilayer hybrid laminates exhibites reversible and controllable shape deformation behavior. • Addition of copper ions improved photothermal conversion capability of TDN/PDMS bilayer hybrid laminates. • Janus, thermal responsiveness, and photothermal transformation realized shape transformation. • High toughness and reversible shape deformation controlled by temperature, thickness ratio and metal ion coordination. [ABSTRACT FROM AUTHOR]

Polyampholyte (PA) hydrogels in general possess excellent mechanical properties, but their underwater applications are largely limited due to swelling induced dramatically reduced strength and poor wet adhesion, especially in high salinity environments. Here, we report our approach to fabricating an anti-swelling poly(acryloyloxyethyltrimethyl ammonium chloride (DAC) -co- sodium p-styrenesulfonate (NaSS) -co- 2-Vinyl-4,6-diamino-1,3,5-triazine (VDT), or P(DAC -co- NaSS -co- VDT), PA hydrogel by introducing multi-hydrogen bonding capable functional VDT moieties into the DAC/NaSS coexisting and cation/anion ratio easily tunable PA network. The mechanical properties of the P(DAC -co- NaSS -co- VDT) hydrogel in bulk and at interface were controllable with dimethyl sulfoxide (DMSO)/H 2 O solvent displacement and Hofmeister effect in a wide salinity range, exhibiting maximum tensile strength, Young's modulus, and wet adhesion toughness of 7.6 MPa, 200 MPa, and 350 J m−2, respectively. The anti-swelling and strong P(DAC -co- NaSS -co- VDT) PA hydrogel developed in this work may find great potential in underwater sensing and sewage treatment as well as for many biomedical applications. • Polyelectrolyte P(DAC -co- NaSS -co- VDT) hydrogels can maintain volume stability in different salt solutions. • Hofmeister effect improves the mechanical properties of hydrogels. • The underwater adhesion of hydrogel can be regulated by solvent exchange. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) is the most heavily used polymer worldwide. Theoretically, PE can be further enhanced by methods such as increasing the molecular weight or moderate cross-linking, however these changes lead to increased viscosity and difficulty for processing PE in the molten state, bringing problems such as decreased production efficiency and greater difficulty in recycling. An important research direction has focused on combining the easy processing and mechanical strength of PE. In this study, long-branched polyethylene containing reversible boronic esters bonds (B–O bonds) was prepared by graft copolymerization, and then PE vitrimers were prepared by a complex decomposition reaction with bis(dioxaborolane) crosslinker. This method can directly convert non-functional conventional plastics into dynamic covalent polymers through reactive processing imparting higher tensile strength, Young's modulus, and better heat resistance to PE. The PE vitrimers is demonstrated to have good melt processability based on dynamic B–O bond exchange, uniting strong mechanical and thermomechanical properties with excellent reproducible processability. This work introduces a new way of recycling and reusing traditional plastic and rubber products. • The introduction of dynamic covalent networks into polyolefins through rational design directly converting commercial plastics into dynamic covalent materials and improving their mechanical properties. •Despite the formation of a three-dimensional mesh cross-linked structure, the material is reprocessable and recyclable due to its dynamic properties. •The rheological and viscoelastic properties of dynamic cross-linked polyethylene materials are investigated to provide ideas for the design of dynamic covalent materials of polyolefins. [ABSTRACT FROM AUTHOR]

Tough hydrogels with adjustable stiffness are expected for adapting application as various biomaterials. Oppositely charged polyelectrolytes form tough and self-healing physical polyion-complex (PIC) hydrogels via formation of inter-chain ionic bonds with a wide distribution in bond strength. The strong bonds serve as permanent crosslinking to impart elasticity and the weak bonds as reversible sacrificial bonds to dissipate energy and to self-heal. In this work, we fabricate four PIC hydrogels using four positively charged trimethyl-ammonium monomers with slightly different chemical moieties and a same negatively charged polymer. The obtained PIC hydrogels all show high toughness but large difference in stiffness, extensibility, and self-recovery kinetics. With slight difference in the monomer structure of the polycations, the modulus of the hydrogels varies over two orders in magnitude, from 0.36 to 56 MPa, and the difference in elongation at break is up to five times. The presence of acryloyl moiety and methyl moiety increase the stiffness of the hydrogels. In the temperature range studied, all the four PIC hydrogels exhibit the rheological simple behaviours, following the time-temperature superposition principle. The four samples show quite different dynamic relaxation spectra over wide frequency range, revealing large difference in the strength distribution of dynamic ionic bonds. SEM observation reveals quite different phase separation structure for the four samples, in which the polymer chain stiffness should play an important role. This understanding of structure-properties of the PIC hydrogels will merit the designing of various supramolecular tough hydrogels and therefore broaden the scope of hydrogels for the applications as biomaterials. [ABSTRACT FROM AUTHOR]

Most of the currently developed flexible energy storage devices lack sufficient flexibility to withstand various deformations, such as stretching, compression, and bending under the action of external forces. It also lacks sufficient and stable energy output. In this work, we use the flexible material hydrogel as electrode and electrolyte to design an all-hydrogel integrated flexible supercapacitor. Both the electrode and the electrolyte contain the same polyampholyte hydrogel P(NaSS- co -DMAEA-Q) matrix, making them possess superb self-adhesion due to the electrostatic interaction between the anion and cation group, and highly softness/toughness thanks to the energy-dissipative mechanism. The electrode of supercapacitor is a composite of activated carbon and hydrogel, which has e xcellent mechanical and electrical properties. Supercapacitors prepared from hydrogel electrodes and hydrogel electrolytes are inherently scalable/compressible, and simultaneously deliver high areal capacitance (128.9 mF cm−2 at 1 mV s−1 and 340.18 mF cm−2 at 0.1 mA cm−2) and maintain stable energy output. The combination of simple device structure, stable mechanical properties and excellent electrical properties makes flexible supercapacitors promising for applications in wearable electronics/devices and energy storage. • The same PA-based hydrogel as base material reduce the Interfacial contact resistance to a great extent. • The device has excellent overall stress and strain tolerance and durability. • Satisfied electrochemical performance of the device is evidenced by high areal capacitanceand moderately high power density/energy density. [ABSTRACT FROM AUTHOR]

Naturally occurring polysaccharide-based polyelectrolyte complex (PEC) physical hydrogels have broad applications in biomedicine. Yet, obtaining high-strength, strong-adhesion, and antibacterial PEC hydrogels via physically crosslinking of natural polysaccharides still remains a challenge. In this work, a chitosan (CS)/sodium alginate (SA) PEC physical hydrogel film was developed by using two oppositely charged natural polysaccharides, CS and SA, of equivalently high molecular weight (M w , approx. 105 Da), the tensile stress of which was achieved as high as 12.3 MPa due to CS-CS intermolecular hydrogen bonding and CS-SA electrostatic interaction. In addition, the hydrogel films, upon protonation at acidic conditions (e.g. pH 2.6), exhibited excellent antibacterial activity against Escherichia coli (E. coli) and the CS/SA hydrogel films also demonstrated strong adhesion to biological tissue. The high M w -matching, two-component natural polysaccharide approach presented in this work to preparing high-strength, strong-adhesion, and antibacterial PEC hydrogels may shed some lights on converting renewable biomass to value-added biomaterials. The hydrogel films (CS/SA) prepared by self-assembly of chitosan (CS) and sodium alginate (SA) with high molecular weight have a large number of hydrogen bonds and electrostatic interactions, the synergistic effect of those two makes the hydrogel have excellent mechanical properties. This hydrogel films also have strong tissue adhesion and bacteriostatic properties, with which the hydrogel films could be used for converting renewable biomass to value-added biomaterials. [Display omitted] • The hydrogen bonds and electrostatic interactions of CS/SA gel made it have excellent mechanical properties. • Ag+ made the CS/SA hydrogel films exhibited excellent mechanical properties and antibacterial activity. • The CS/SA hydrogels demonstrated excellent adhesion to biological tissues and promptly closed a wound. [ABSTRACT FROM AUTHOR]

The application of polyethylene in artificial turf promotes research on the processing and properties of uniaxial extension modified polyethylene materials. The effects of comonomer (octene/butene) structure on the properties of pre-stretched linear low density polyethylene (LLDPE)/polyolefin elastomer (POE) blends are investigated. The melt tensile stress and melt stretch ratio of LLDPE ethylene‒octene copolymer (EOC)/POE reach 4.0 × 105 Pa and 12.8, respectively. At the pre-stretching ratio λ = 5, the tensile strength of EOC/POE λ5 reaches 62.5 MPa, the critical length is 5.7 mm, and the strain hardening degree increases. Differential scanning calorimetry, Raman spectroscopy and X-ray diffraction show the crystallinity of EOC/POE λ5 is higher than that of LLDPE ethylene‒butene copolymer (EBC)/POE λ5. Large short-chain branch length EOC is demonstrated to rebuild the "physical crosslinking point" after pre-stretched, thereby enhancing the interaction between molecular chains in EOC/POE λ5. This research provides a new clue for the development of artificial turf materials. [Display omitted] • Pre-stretched ethylene‒octene copolymer/polyolefin elastomer blends are researched. • Pre-stretching improves mechanical properties of blends. • "Physical crosslinking points" strengthens inter-chain-segmental forces. [ABSTRACT FROM AUTHOR]

Hydrogels that possess adequate toughness in bulk and at soft interface are highly desirable. We report a fully physically crosslinked dual Amylopectin (Amy, the first network)/poly(N-hydroxyethyl acrylamide) (PHEAA, the second network) hydrogel, where both networks were hydrogen bonding (H-bonding) crosslinked, with super toughness in bulk and tunable adhesion at hydrogel-soft tissue interface. Through adjustment of hydrogen bond density, strong and tough hydrogels were prepared that exhibited different levels of adhesion strength and three adhesive failure mechanisms. We replaced Amy with oxidized starch (OSA) to synthesize dual and hybrid chemically/physically crosslinked OSA/PHEAA double network (DN) hydrogels that were capable of forming Schiff's bases at hydrogel-hydrogel or hydrogel-tissue interfaces, aside from interfacial H-bonding, incurring sustained, high interfacial toughness (1850 J m−2 hydrogel-hydrogel and 610 J m−2 hydrogel-tissue) in wet environments. Such tough and adhesive DN hydrogels have great potential in various applications such as engineering of artificial soft tissues or implantable devices that are intended to adhere to internal organs or tissues. • Fully physically crosslinked hydrogels via H-bonding. • Tunable adhesion and three adhesive failure mechanisms of hydrogels. • The sacrificial bonds including H-bonds and reversible Schiff's bases at the interface. • High interfacial toughness at hydrogel-hydrogel or hydrogel-tissue interfaces in wet environments. [ABSTRACT FROM AUTHOR]