Search

Hydrogels have been attracting great attention on account of their soft and wet nature, but inherently poor and unbalanced mechanical performance severely limits their applications. Herein, we repo...

Fire prevention and safety of combustible materials is a global challenge. To reduce their high fire risk, traditional smoke detectors are widely used indoor via detecting smoke product after combustion; however, they usually show a long response time and limitation for outdoor use. Herein, we report a temperature-induced electrical resistance transition of graphene oxide wide-ribbon (GOWR) wrapped sponges to reliably monitor fire safety of the combustible materials. Novel rectangle-like GOWR sheets are synthesized from unzipping carbon nanofibers and used to fabricate GOWR wrapped melamine formaldehyde sponges with multi-functionalities, e.g. lightweight, good hydrophobicity, reversible compressibility, excellent acidic/alkaline tolerance and flame resistance. The GOWR sheets on the sponge skeleton can be in-situ thermally reduced once encountering a flame attack or abnormal high temperature, inducing a distinct transition in electrical resistance. Consequently, an ultrafast alarm response of ∼2 s to flame attack is triggered, and rapid fire early warning signals to abnormal high temperatures, e.g. ∼33 s at 300 °C, are achieved below ignition temperature of most combustible materials. This method drives substantial motivation and opportunity to develop advanced fire detection and early warning sensors for reducing the high fire risk of various combustible materials in outdoor applications.

Hyperbranched polysiloxane (HSi) molecules with tunable molecular structure were synthesized and served as a novel crosslinker for fabricating polyacrylamide/chitosan (PCH) hydrogels. Various characterizations demonstrated that HSi molecules with tunable bi-functional vinyl and epoxy groups were successful prepared and utilized to optimize the network architecture and interactions of polymer chains. Benefiting from the structure of bi-functional crosslinker, PCH hydrogels demonstrated remarkably improved mechanical properties, superior to that of conventional crosslinker or HSi with single vinyl or epoxy group. A tensile strength of 302 kPa, elongation at break of 2263%, and toughness of 3.85 MJ·m–3 can be achieved by optimizing the molecular structure and content of HSi with bi-functional group (e.g. ratio of vinyl/epoxy = 0.68). Additionally, such hydrogels showed outstanding antifatigue ability to withstand cyclic compressive tests. Based on the structure observation and analysis, the improved mechanical properties are likely derived from the combination of homogeneous and strong polymer network and improved interactions of polymer chains (e.g. covalent and hydrogen bonds). Approaches in this study may inspire the design and development of novel crosslinker for fabricating mechanically robust hydrogels. Keywords: Hyperbranched polysiloxane, Tunable molecular structure, Hydrogel, Mechanical properties, Chitosan

Graphene oxide nanoribbons (GONRs) were synthesized and functionalized by silane molecules with different hydrophobic end-groups, and silane functionalized reduced GONR (silane-f-rGONR) coated polyurethane (PU) sponge composites were fabricated via a facile dip-coating process. Fourier-transform infrared, Raman spectrum, X-ray photoelectron spectroscopy and scanning electron microscopy demonstrated that silane molecules were successfully grafted onto GONR sheets, thus producing the ability to tune surface and physical properties of PU sponge from insulating and hydrophobic to conductive and super-hydrophobic. Cyclic compression and strain-induced electrical resistance change tests indicated that the porous silane-f-rGONR coated PU (silane-f-rGONR@PU) sponge composites exhibited excellent mechanical elasticity and durability and high sensitivity of resistance change. Furthermore, the two types of silane modified sponges showed different super-hydrophobicity and tunable oleophilicity/oleophobicity. Compared to the rGONR@PU composite with poor oil/water separation at dynamic state, these porous silane-f-rGONR@PU composites not only possessed excellent oil/solvent absorption capacity and selective oil/water separation at static state, but also showed good continuous oil/solvent pumping collection with high recyclability (>97% after 10 cycles) and outstanding oil/water separation efficiency at the dynamic shaking state. This work provides a new strategy for fabricating the super-hydrophobic, electrically conductive and mechanically flexible porous rGONR based composites, showing promising application in strain sensor and oil pollution remediation fields at different environmental conditions.

Conductive hydrogels are promising in the flexible wearable electronic applications due to their unique feature of intrinsic stretchability, reversible flexibility, and high electrical conductivity. However, severely poor adaptability under cold or hot environmental conditions along with inferior adhesiveness to various substrates greatly hinders the potential applications in such emerging field. Herein, we describe a mechanically flexible and electrically conductive nanocomposite hydrogel composed of polyacrylamide-co-acrylic acid/chitosan covalent-network reinforced by Ti3C2Tx MXene nanosheets within water-glycerol binary solvent via a simple one-pot free radical polymerization. Notably, incorporation of a low content (0.1–0.3 wt%) of MXene promotes the rapid gelation of the polymer molecules in only 10 min. The optimized hydrogel containing 0.2 wt% MXene not only possesses excellent mechanical performance (e.g., tensile elongation of ~1000%) and improved electrical conductivity (~1.34 S/m), but also shows stable temperature tolerance from − 20 to 80 °C and self-adhesion with various substrates (e.g., steel, glass, rubber, plastics and skin) as well as a rapid self-healable feature (~1.3 s). Further, such hybrid MXene hydrogel exhibits dual sensations under different strain (1–600%) and stress (80–3200 Pa) ranges, good applicability for various deformation conditions (tension/bend/compression), and wide temperature adoptability with stable repeatability. Clearly, this versatile MXene nanocomposite hydrogel developed may provide a new route for the rational design and development of advanced skin-like sensor for complex environmental application.

Cellulose-based film material, due to its remarkable physicochemical properties, environmentally friend and low cost, has been widely applied in many high-end areas. However, the lack of functional properties (e.g., flame resistance) except poor mechanical performance severely hinders their further applications. Herein, bamboo-based phosphorylated cellulose nanofibrils (B-PCNFs) were prepared through a simple two-step method composed of phosphorylation and mechanical grinding process. The resultant film prepared via solvent casting process shows an excellent mechanical strength of 115.9 MPa, remarkable elongation at break of 53.1%, high Young's modulus of 2.5 GPa and impressive work of fracture up to 41.8 MJ m−3, respectively, which should be contributed to the formation of dense and homogeneous polymer networks reinforced by enhanced multiple interactions. When burned against the flame of alcohol lamp (700–800 °C), BHL-PCNF film also delivers appealing structural stability even over 25s, demonstrating a prominent flame resistance. Meanwhile, compared to original one, the peak heat release rate (PHRR) and total heat released (THR) of BHL-PCNF film produce a dramatical reduction, i.e., 87.3% and 86.6% for PHRR and THR, respectively. Based on the evolution of morphological and chemical structure, the highly improved flame resistance is strongly contributed to the synergy of phosphorus containing group and lignin, resulting in a protective layer composed of PxOy compound and carbon layer. The proposed mechanism for the enhanced flame retardant property is also declared and clarified. Thereby, this phosphorylated cellulose-based film that integrates outstanding mechanical performance and excellent intrinsically flame resistance holds promising potential candidate in practical applications, such as flame-retardant packaging materials.

In the present work, Zn–(0–1)Mg (wt%) alloys were prepared by casting and indirect extrusion at 200 and 300 °C, respectively. With Mg addition, both the size and amount of second phase Mg2Zn11 increased, and the equiaxed grains were significantly refined. The extrusion temperature had little influence on Mg2Zn11, but the grains were refined at low extrusion temperature. For the alloys extruded at 200 °C, as Mg content increased, the tensile yield strength (TYS) increased from 64 MPa for pure Zn to 262 MPa for Zn–1Mg; the elongation increased from 14.3% for pure Zn to 25% for Zn–0.02Mg and then decreased to 5% for Zn–1Mg. For the alloys extruded at 300 °C, as Mg content increased, the TYS increased from 67 MPa for pure Zn to 252 MPa for Zn–1Mg, while the elongation decreased from 11.7% to 2%. The alloy extruded at 200 °C exhibited higher TYS and elongation than the corresponding alloy extruded at 300 °C. The combination of grain refinement and second phase Mg2Zn11 contributed to the improvement in the TYS, and the grain refinement played a major role in strengthening alloy. Zn–0.02Mg and Zn–0.05Mg alloys extruded at 200 °C show a mixture of cleavage and ductile fracture corresponding to higher elongation, while the other alloys show cleavage fracture.

In this work, hydroxyl-terminated polydimethylsiloxane (H-t-PDMS) nanocomposites reinforced by different contents of graphene oxide nanoribbons (GONRs) were prepared via a facile solvent-free process, and the mechanical properties of the H-t-PDMS/GONR nanocomposites were investigated and compared with the corresponding nanocomposites containing pristine carbon nanotubes (CNTs) or functionalized CNTs (f-CNTs). It was found that the GONRs with abundant functional groups showed good compatibility with the H-t-PDMS matrix at appropriate content: both good dispersion levels of the GONR sheets and strong GONR/matrix interfacial interactions were achieved at low filler content (≤0.5 wt%), although the GONR sheets showed obvious clusters in the matrix at relatively high content. Mechanical testing indicated that the incorporation of a low content of GONRs into the H-t-PDMS polymer resulted in significant improvements in both the tensile and tear strengths, e.g. about 158 and 284% at 0.5 wt% GONRs, respectively; and such reinforcement efficiency of the GONRs in the PDMS nanocomposites was much better than those of the corresponding CNTs or f-CNTs, even superior to those of other carbon nanofillers in previous PDMS-based nanocomposite systems. Based on the morphology and fracture surface analysis, the possible reinforcing mechanisms were discussed and clarified to understand the discrepancies in the mechanical properties of the nanocomposite systems studied.

Water-based hybrid graphene oxide nanoribbon (GONR)/montmorillonite (MMT)/polyethylene glycol (PEG) networks were prepared by using a facile bio-inspired low-temperature evaporation induced assembling process. Multiple non-covalent and covalent interactions together with a high orientation level of MMT were constructed in the hybrid PEG/MMT/GONR networks. As a result, the hybrid networks exhibit synergistic reinforcing and toughening efficiencies when compared with the composites modified with the single-phase filler, e.g. 152% and 167% increase in tensile strength for the optimized ternary composites in comparison with those of the binary composites. Moreover, the nacre-like hybrid networks show excellent flame resistance and structural stability in a flame due to the formation of interconnected and compact char after combustion, which can be applied as protective coatings to combustible materials. The hybrid coatings not only improve the flame-retardant property (e.g. ~46% decrease in heat release rate at 30 wt%) of the combustible PU foam materials significantly, but also provide ideal fire alarm responses (e.g. rapid flame detection of ~2 s and effective fire early warning signals in pre-combustion). Owing to the green and versatile synthesis scheme, excellent mechanical performance and flame resistance, these hybrid PEG/MMT/GONR networks are promising widespread application.

Hydrogels with exceptional mechanical properties at high water content are crucial need for practical applications in various fields. However, achieving a hydrogel possessed splendid mechanical performance with well trade-off between tensile strength and toughness is highly demanded due to the mechanical weakness of conventional hydrogel. Herein, we report a novel kind of nanocomposite hydrogel developed by integrating chitosan decorated halloysite nanotubes (CS-f-HNTs) into dual cross-linked structure composed of chemical and Fe3+ induced ionically cross-linked network. Combining the nanoparticle reinforcement with physical interactions including hydrogen bonds among polymer chains and ionic coordination interaction between Fe3+ ions and functional groups on chitosan chains and the copolymer chains, the hydrogel exhibits extraordinary and balanced mechanical performance, including high strength (3.06 MPa), outstanding stretchability (>2000%) and superior toughness (47.6 MJ m−3) in which water content remains ~80 wt%. Based on microstructure observation and dynamic mechanical behavior analysis, we demonstrated that the addition of CS-f-HNTs effectively bridged polymer chains via physical interactions and strengthened dual cross-linked network, leading to significant improved mechanical properties. Moreover, the hydrogels also possessed remarkable self-recoverability (97.9% for small strain (200%) and 91.5% for large strain (1000%)) at room temperature and the related mechanism was discussed. The strategy developed herein may provide a newfound avenue in the design and development of strong and tough hydrogel for promising applications in loading-bearing structural materials.

Hydrogels with a combination of high mechanical properties and excellent electrical conductivity are promising for soft and wearable electronics devices. However, the trade-off between poor strength/toughness and high electrical resistance of the hydrogels severely hamper their practical application in diverse areas. In this work, we reported a facile and effective strategy for fabricating mechanically robust and electrically conductive nanocomposite hydrogels via incorporating chitosan in-situ grafted magnetite nanoparticles combined with multiple ionic-covalent interactions. The obtained nanocomposite hydrogel delivers a remarkable mechanical strength up to 2.33 MPa and high toughness of 18.18 MJ m-3 at a relatively high water content (80 wt%). Based on the creep/recovery experimental results and analysis (Burger's model and Weibull distribution function), the effect of multiple ionic-covalent interactions among the double-networks and chitosan in-situ grafted nanoparticles on the viscoelastic behavior of the hydrogel was discussed and clarified. In addition, the resultant nanocomposite hydrogel exhibits sensitive strain-induced resistance change under both compressive and tensile stress as well as outstanding stability and repeatability, which can accurately and repeatedly monitor both large mechanical deformation (e.g. tensile strain up to 600%) and human behaviors (e.g., motions of joints and facial expressions). This study offers a new scenario to design and develop a mechanically robust hydrogel with sensitive strain-responsive resistance, showing potential applications in electric skin, motion detection, wearable electronics, etc.

Graphene oxide (GO) paper with outstanding integrated multiple functionalities (good mechanical performance, thermal stability and flame resistance, etc.) is strongly needed for numerous potential applications in cutting-edge fields. In this work, we report a facile and green process to fabricate GO-based nanocomposite papers via introducing functionalized silica (f-SiO2) nanoparticles. The results reveal that addition of f-SiO2 produces simultaneous improvements in mechanical strength, stiffness and flame resistance for GO paper. With incorporation of 10 wt% f-SiO2, the tensile strength, elastic modulus and toughness of the GO/f-SiO2 nanocomposite papers can be increased by about 51%, 317%, and 69%, respectively. Various characterizations disclose that hydrogen bonds and covalent interactions between GO sheets and f-SiO2 mainly contribute to the effective load transfer and energy dissipation between them, and thus leading to the improvements of mechanical properties. Based on the structural observation and analysis, the improved flame resistance of the GO/f-SiO2 papers should be attributed to the formation of rGO/SiO2 protective char, which are derived from the decomposition and redeposition of the grafted silane molecules and inorganic SiO2 and thermal reduction of GO into rGO. Our results suggest that the mechanical and thermal properties of GO papers can be tuned by introducing inorganic/organic f-SiO2, providing a new route for the rational designing and development of mechanically flexible and flame-retardant GO-based nanocomposite paper materials.

AIM:To investigate the application of confocal laser scanning microscopy (CLSM) in tumor pathology and three-dimensional (3-D) reconstruction by CLSM in pathologic specimens of hepatocellular carcinoma (HCC).METHODS:The 30mgr;m thick sections were cut from the paraffin embedded tissues of HCC, hyperplasia and normal liver,stained with DNA fluorescent probe YOYO-1 iodide and examined by CLSM to collect optical sections of nuclei and 3-D images reconstructed.RESULTS:HCC displayed chaotic arrangement of carcinoma cell nuclei, marked pleomorphism, indented and irregular nuclear surface, and irregular and coarse chromatin texture.CONCLUSION:The serial optical tomograms of CLSM can be used to create 3-D reconstruction of cancer cell nuclei. Such 3-D impressions might be helpful or even essential in making an accurate diagnosis.