Highly ordered structured montmorillonite/brominated butyl rubber nanocomposites: Dramatic enhancement of the gas barrier properties by an external magnetic field

Magneto-Induced Janus Adhesive-Tough Hydrogels for Wearable Human Motion Sensing and Enhanced Low-Grade Heat Harvesting

Janus hydrogels with different properties on the two surfaces have considerable potential in the field of material engineering applications. Various Janus hydrogels have been developed, but there are still some problems, such as stress mismatch caused by the double-layer structure and Janus failure caused by material diffusion in the gradient structure. Here, we report a Janus adhesive-tough hydrogel with polydopamine-decorated Fe3O4 nanoparticles (Fe3O4@PDA) at one side induced by magnetic field to avoid uncontrollable material diffusion in the cross-linking polymerization of acrylamide with alginate-calcium. The magneto-induced Janus (MIJ) hydrogel has an adhesive surface and a tough bulk without an obvious interface to avoid stress mismatch. Due to the intrinsic dissipative matrix and the abundant catechol groups on the adhesive surface, it shows strong adhesion onto various substrates. The MIJ hydrogel has high sensitivity (GF = 0.842) in detecting tiny human motion. Owing to the synergy of Fe3O4@PDA-enhanced interfacial adhesion and heat transfer, it is possible to quickly generate effective temperature differences when adhering to human skin. The MIJ hydrogel achieves a Seebeck coefficient of 13.01 mV·K-1 and an output power of 462.02 mW·m-2 at a 20 K temperature difference. This work proposes a novel strategy to construct Janus hydrogels for flexible wearable devices in human motion sensing and low-grade heat harvesting.

Excellent Oxygen Barrier Property of Unfilled Natural Rubber/trans-Butadiene-co-Isoprene Rubber Vulcanizates under the Synergistic Effect of Crosslinking Density and Crystallization

The thermo-oxidative aging of rubber products is inevitable during their use and leads to product failure and can even endanger safety. Oxygen is an important factor that cannot be ignored during the thermo-oxidative aging process. Thus, the gas barrier property of rubber products is of significant concern. In this work, a strategy of crystallizing rubber in unfilled rubber composites was designed by firstly constructing a dual synergistic mechanism of crosslinking density and crystallization on the oxygen barrier properties. As a crystallizable polymer, trans-butadiene-co-isoprene rubber (TBIR) shows dendritic fibril crystals or spherulites in natural rubber (NR)/TBIR vulcanizates. Meanwhile, the vulcanizates containing TBIR have a higher crosslinking density than NR vulcanizates. These TBIR-rich crystals and high-crosslinking-density structures are distributed in vulcanizates like continuous islands. Contrary to what has been reported in the literature, the decrease in oxygen permeability of NR/TBIR is not only due to the high crosslinking density and free volume of the polymer matrix, but more importantly, the spherulites of TBIR play a role in blocking and prolonging the oxygen diffusion path during the diffusion of oxygen in the polymer composites. We propose that the compatible crystalline polymer can replace the lamellar filler, play the role of the oxygen barrier in rubber composites, reduce the diffusion and dissolution of oxygen, and achieve the effect of improving the thermo-oxidative aging property of the rubber composite. Future research will follow the morphology evolution of TBIR crystals, their crosslinking structure and density, and interactions between TBIR and NR on the oxygen barrier and thermo-oxidative aging property.

Effect of Graphene Oxide-Modified CaAl-Layered Double Hydroxides on the Carbon Dioxide Permeation Properties of Fluoroelastomers

This work aimed to investigate the CO2 gas barrier and mechanical properties of fluorine rubber nanocomposites filled with Ca/Al layered hydroxide (graphene oxide [GO]/LDH-Ca2Al) modified by GO. GO/LDH-Ca2Al nanocomposite fillers were prepared by depositing Ca/Al layered hydroxide (LDH-Ca2Al) into the surface of alkalized GO (Al-GO). The prepared GO/LDH-Ca2Al nanocomposite fillers and complexes were characterized by Fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) for structural and micromorphological characterization. The results showed that GO/LDH-Ca2Al was successfully prepared with strong interactions between Al-GO and LDH, and the compatibility of GO/LDH-Ca2Al nanocomposite fillers with the polymer was significantly improved compared with that of LDH-Ca2Al. Consequently, both the fracture strength (σb) and strain (εb) of GO/LDH-Ca2Al nanocomplexes remarkably increased, and they exhibited excellent mechanical properties. Differential scanning calorimetry and thermogravimetric analysis were used to characterize the thermal stability of GO/LDH-Ca2Al nanocomposite fillers, and GO/LDH-Ca2Al nanocomposite fillers have better thermal stability than LDH-Ca2Al. The reaction products (S-LDH-Ca2Al and S-GO-Ca2Al) of LDH-Ca2Al and GO/LDH-Ca2Al with CO2 were characterized using XRD and TGA, respectively, and the results show that LDH-Ca2Al reacts readily and chemically with CO2, resulting in a lower diffusion coefficient of CO2 in the LDH-Ca2Al nanocomplexes than that of the GO/LDH-Ca2Al nanocomplexes and leading to the destruction of the laminar structure of LDH-Ca2Al, while GO/LDH-Ca2Al has better CO2 resistance stability. GO/LDH-Ca2Al nanocomplexes exhibited a reduced content of hydroxyl groups with pro-CO2 nature exposed on the surface of LDH-Ca2Al, improving the interfacial interaction between the nanofillers and the rubber matrix and enhancing the dispersion of GO/LDH-Ca2Al in the polymers. Moreover, CO2 in the soluble GO/LDH-Ca2Al nanocomposites was significantly reduced, while the diffusion properties demonstrated weak temperature dependence on solubility. The mechanism of the CO2 gas barrier of polymers filled with GO/LDH-Ca2Al was proposed on the basis of the Arrhenius equation.

Effects of soil colloids on the aggregation and degradation of engineered nanoparticles (Ti3C2Tx MXene)

Soil colloid is a nonnegligible factor when evaluating the environmental risk of engineered nanoparticles (ENPs) in the groundwater. In this study, the environmental fate of an emerging ENP (Ti₃C₂T_x MXene) in the groundwater was investigated for the first time, which currently poses a severe environmental risk due to its cytotoxicity but has received little attention. The colloidal dispersion stability and degradation kinetics of Ti₃C₂T_x MXene in the groundwater were evaluated by considering the effects of soil colloids prepared from sodium humate (SH), montmorillonite (MT), and a natural soil (NS) under variable solution chemistry. The results showed that the affinity of soil colloids with Ti₃C₂T_x followed an SH > MT > NS sequence. Increasing SH concentration led to Ti₃C₂T_x disaggregation by enhancing the electrical and steric repulsive forces, while MT and NS resulted in hetero-aggregation because of the elevated collision frequency. SH and MT enhanced the critical coagulation concentrations of Ti₃C₂T_x by 100 and 10 folders, respectively, via surface coating process, while NS slightly reduced due to the bridging effects induced by the soluble cations. The soil colloids promoted Ti₃C₂T_x degradation compared with their absence and in an SH > MT ≫ NS sequence. SH and MT were through forming Ti-O-C and Si-O-Ti bonds with Ti₃C₂T_x via their carboxyl and hydroxyl groups, respectively, rendering the Ti₃C₂T_x surface more reactive and faster degradation. NS showed a weak promotion effect because of its less affinity with Ti₃C₂T_x and limited organic matter and clay contents with hydroxyl and carboxyl groups. This study demonstrated the unstable environmental behaviors of Ti₃C₂T_x in the groundwater and mitigated its environmental risk concerns.

Constructing Oriented Two-Dimensional Large-Sized Modified Graphene Oxide Barrier Walls in Brominated Butyl Rubber to Achieve Excellent Gas Barrier Properties

Brominated butyl rubber (BIIR) is widely used as tire lining, medical sealing material, and so on, due to its merits like high strength, low permeability, and high vulcanization activity. However, the gas barrier properties of BIIR need to be improved further to meet the requirements of certain special conditions such as high pressure (aircraft tire: 1.5 MPa). In this work, oriented two-dimensional (2D) large-sized modified graphene oxide (mGO) barrier walls in BIIR are successfully constructed based on the following processes: three-dimensional (3D) large-sized mGO hollow spherical shells in BIIR matrix are achieved from the core (water)-shell (mGO) structure in BIIR solution, which is obtained through the Pickering emulsion template method, and then are pressed into oriented 2D large-sized mGO barrier walls in the BIIR matrix. Such oriented 2D large-sized mGO barrier walls not only have an extremely large size between 50 and 120 μm but also are aligned perpendicular to the gas diffusion direction. Thus, even only with 0.7 wt % mGO, the nitrogen permeability of the BIIR composite is reduced by 91% relative to pristine BIIR and by 40% relative to the comparing sample with small mGO sheets. Therefore, this work provides a route to regulate the distribution of GO and thus can be a useful reference to fabricate rubber composites with superior gas barrier properties.

Self-assembly of chemically modified graphene sheets in an external magnetic field

The rapid developments of effective self-assembly technologies indicated that ordered structures could be produced using external field inducement. We designed the alignment of graphene oxide nanosheets grafted with the modified ferroferric oxide by the application of a magnetic field. The results indicated that the morphologies of graphene oxide went through some changes from disordered to semi-ordered in the final and, highly oriented wrinkled structures. The orientation mechanism of graphene oxide demonstrated that the geometric features of the wrinkles were related to the edge stresses and the elastic stiffness of the sheets, magnetic force of magnetic field to magnetic-particles. The prepared reduced graphene oxide fibers indicated that the sheets with magnetic precipitates underwent shrinkage in the radial direction when an external magnetic field was exerted and the interior sheets aligned along the direction of the magnetic field, which was supported by the proposed theories. It is expected that the research could contribute to the applications of flexible graphene-based materials in preparation and controlling the formation of wrinkles in single layer graphene.

Barrier Properties of Layered-Silicate Reinforced Ethylenepropylenediene Monomer/Chloroprene Rubber Nanorubbers

The triacetin and nitroglycerin barrier properties of layered-silicate reinforced ethylenepropylenediene monomer/chloroprene rubber (EPDM/CR) nanorubbers were investigated as rocket-propellant inhibitors. EPDM/CR nanorubbers with intercalated structures were formulated and prepared by the melt-compounding method. The triacetin permeability and nitroglycerin absorption were observed to decrease with increasing layered-silicate content. The layered silicates also improved the flame retardancies of the nanorubbers by forming silicate reinforced carbonaceous chars. Layered-silicate reinforced EPDM/CR nanorubbers are potentially effective rocket propellant-inhibiting materials.