The effect of dispersion state of graphene on mechanical properties of graphene/epoxy composites was investigated. The graphene sheets were exfoliated from graphite oxide (GO) via thermal reduction (thermally reduced GO, RGO). Different dispersions of RGO sheets were prepared with and without ball mill mixing. It was found that the composites with highly dispersed RGO showed higher glass transition temperature (Tg) and strength than those with poorly dispersed RGO, although no significant differences in both the tensile and flexural moduli are caused by the different dispersion levels. In particular, the Tg was increased by nearly 11 °C with the addition of 0.2 wt.% well dispersed RGO to epoxy. As expected, the highly dispersed RGO also produced one or two orders of magnitude higher electrical conductivity than the corresponding poorly dispersed RGO. Furthermore, an improved quasi-static fracture toughness (KIC) was measured in the case of good dispersion. The poorly and highly dispersed RGO at 0.2 wt.% loading resulted in about 24% and 52% improvement in KIC of cured epoxy thermosets, respectively. RGO sheets were observed to bridge the micro-crack and debond/delaminate during fracture process due to the poor filler/matrix and filler/filler interface, which should be the key elements of the toughening effect. 相似文献
2D graphene with high quality holds great promise in improving the performance of the hydrogels owing to its exceptional electronic, thermal, and mechanical properties. However, the structure defects existed in graphene restrict its further applications. Herein, a simple and green method of fabricating defect‐free graphene nanosheets with the assistance of supercritical carbon dioxide (SC CO2) is designed. The graphene nanosheets directly assemble with acrylic acid monomer and clay, and a flexible semitransparent hydrogel is fabricated. Benefiting from the excellent properties of the defect‐free graphene, the hydrogel exhibits the high mechanical performance, superfast self‐healing capability, excellent conductivity, and super photothermal conversion efficiency. According to the advantages above, the graphene/poly(acrylic acid)/clay hydrogels can be used for intelligent sensors for disease diagnosis, artificial electronic skin, and military stealth materials in the near future. 相似文献
A dual cross‐linking design principle enables access to hydrogels with high strength, toughness, fast self‐recovery, and robust fatigue resistant properties. Imidazole (IMZ) containing random poly(acrylamide‐co‐vinylimidazole) based hydrogels are synthesized in the presence of Ni2+ ions with low density of chemical cross‐linking. The IMZ‐Ni2+ metal–ligand cross‐links act as sacrificial motifs to effectively dissipate energy during mechanical loading of the hydrogel. The hydrogel mechanical properties can be tuned by varying the mol% of vinylimidazole (VIMZ) in the copolymer and by changing the VIMZ/Ni2+ ratio. The resultant metallogels under optimal conditions (15 mol% VIMZ and VIMZ/Ni2+ = 2:1) show the best mechanical properties such as high tensile strength (750 kPa) and elastic modulus (190 kPa), combined with high fracture energy (1580 J m?2) and stretchability (800–900% strain). The hydrogels are pH responsive and the extent of energy dissipation can be drastically reduced by exposure to acidic pH. These hydrogels also exhibit excellent anti‐fatigue properties (complete recovery of dissipated energy within 10 min after ten successive loading–unloading cycles at 400% strain), high compressive strength without fracture (17 MPa at 96% strain), and self‐healing capability due to the reversible dissociation and re‐association of the metal ion mediated cross‐links. 相似文献
Development of artificial soft materials that have good mechanical performances and autonomous healing ability is a longstanding pursuit but remains challenging. This work reports a kind of highly flexible, tough, and self‐healable poly(acrylic acid)/Fe(III) (PAA/Fe(III)) hydrogels. The hydrogels are dually cross‐linked by triblock copolymer micelles and ionic interaction between Fe(III) and carboxyl groups. Due to the coexistence of these two cross‐linking points, the resulting PAA/Fe(III) hydrogels are tough and can be flexibly stretched, bent, knotted, and twisted. The hydrogels can withstand a deformation of 600% and an ultimate stress as high as 250 kPa. Moreover, the dynamic ionic interaction also endows the hydrogels self‐healing properties. By varying the ratio of Fe(III)/AA, a compromised healing efficiency of 73% and an ultimate stress of 200 kPa are obtained.
Graphene oxide (GO), NaF and CaCl2 were mixed in their aqueous solutions to obtain a GO–CaF2 hybrid with CaF2 particles uniformly dispersed on GO surface, and further in situ reduced by hydrazine to obtain reduced-GO (RGO)-CaF2 hybrid. RGO–CaF2/brominated butyl rubber (BIIR) composites were obtained by solution mixing, in which RGO–CaF2 was well dispersed in nano-sized as confirmed by transmission electron microscope images. The RGO–CaF2/BIIR composites had much better mechanical properties than BIIR. The stress at 300% extension of BIIR increased 72% after the addition of 3 parts per hundreds of rubber (phr) RGO–CaF2. The improved mechanical properties benefited from the strong interaction between RGO and BIIR. The dielectric constant of RGO–CaF2/BIIR composites increased with increasing RGO–CaF2 loading. Because of the synergistic effect of RGO and CaF2, the stresses at various extensions, dielectric constant and thermal conductivity of RGO–CaF2/BIIR composites were higher than those of RGO/BIIR or CaF2/BIIR composites. The improved mechanical, dielectric and thermal properties bring BIIR the potential to be used in a wider range of application areas. 相似文献
It remains a challenge to develop tough hydrogels with recoverable or healable properties after damage. Herein, a new nanocomposite double‐network hydrogel (NC‐DN) consisting of first agar network and a homogeneous vinyl‐functionalized silica nanoparticles (VSNPs) macro‐crosslinked polyacrylamide (PAM) second network is reported. VSNPs are prepared via sol‐gel process using vinyltriethoxysilane as a silicon source. Then, Agar/PAM‐SiO2 NC‐DN hydrogels are fabricated by dual physically hydrogen bonds and VSNPs macro‐crosslinking. Under deformation, the reversible hydrogen bonds in agar network and PAM nanocomposite network successively break to dissipate energy and then recombine to recover the network, while VSNPs in the second network could effectively transfer stress to the network chains grafted on their surfaces and maintain the gel network. As a result, the optimal NC‐DN hydrogels exhibit ultrastretchable (fracture strain 7822%), super tough (fracture toughness 18.22 MJ m‐3, tensile strength 431 kPa), rapidly recoverable (≈92% toughness recovery after 5 min resting at room temperature), and self‐healable (can be stretched to 1331% after healing) properties. The newly designed Agar/PAM‐SiO2 NC‐DN hydrogels with tunable network structure and mechanical properties by multi‐bond crosslinking provide a new avenue to better understand the fundamental structure‐property relationship of DN hydrogels and broaden the current hydrogel research and applications. 相似文献
Hydrogels, especially the ones with self‐recovery and adhesive performances, have attracted more and more attention owing to their wide practical potential in the biomedical field involving cell delivery, wound filling, and tissue engineering. Tannic acid (TA), a nature‐derived gallol‐rich polyphenol, exhibits not only unique chelating properties with transition metal cations but also desirable anti‐oxidation properties and strong bonding capability to proteins and gelatin. Thus, taking advantage of the versatility of TA, a one‐pot method is proposed herein to produce TA‐modified gelatin hydrogels with the aid of NaIO4 under basic conditions. By changing the amount of NaIO4 used, the obtained hydrogels are covalently cross‐linked to different degrees and consequently exhibit diversity in their self‐healing and adhesive properties. The gelling time, viscoelasticity, and morphology of hydrogels are investigated, and when the feed molar ratio of NaIO4 to TA is adjusted to 15:1, the fabricated hydrogel shows optimum self‐healing efficiency of 73% and adhesive strength of 36 kPa. Additionally, considering the completely natural origin of TA and gelatin, this study offers an original way for the fabrication of biocompatible self‐healing and adhesive materials. 相似文献
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. 相似文献
This article aims to investigate the impact of reduced graphene oxide (RGO) nanofillers on the curing kinetics, thermal stability, mechanical modulus, electrical conductivity, and EMI shielding effectiveness of unsaturated polyester resin (UPR). The curing rates of UPR/styrene (60/40 by wt%) mixtures with small amounts of RGO (0.1–0.3 wt%) exhibit slight delays owing to the barrier and scavenger roles of 2-dimensional RGO sheets. Nonetheless, it is observed that within the cured nanocomposites, RGOs are effectively dispersed and firmly bonded to the UPR matrix at interfaces through hydrogen bonding and π-π interactions. Consequently, the nanocomposites display heightened thermal decomposition temperatures and increased residue at 800°C with higher RGO loading content. The addition of RGO notably improves the elastic storage modulus and increases the temperature associated with glass transition-related relaxation. The electrical percolation threshold is attained at a specific RGO loading between 0.2 and 0.3 wt%. Thus, the nanocomposite with 0.3 wt% RGO is characterized to have an electrical conductivity of 1.9 × 10−6 S/cm and an EMI shielding effectiveness of ~9 dB at 8 GHz, for a thickness of 1 mm. 相似文献