An in situ forming hydrogel has emerged as a promising wound dressing recently. As physically crosslinked hydrogels are normally unstable, most in situ forming hydrogels are chemically cross-linked. However, big concerns have remained regarding the slow gelation and the potential toxicity of residual functional groups from cross-linkers or the polymer matrix. Herein, we report a sprayable in situ forming hydrogel composed of poly(Nisopropylacrylamide 166 -co-n-butyl acrylate 9 )-poly(ethylene glycol)-poly(N-isopropylacrylamide 166 -co-n-butyl acrylate 9 ) copolymer (P(NIPAM 166 -co-nBA 9 )-PEG-P(NIPAM 166 -co-nBA 9 ), denoted as PEP) and silver-nanoparticles-decorated reduced graphene oxide nanosheets (Ag@rGO, denoted as AG) in response to skin temperature. This thermoresponsive hydrogel exhibits intriguing sol−gel irreversibility at low temperatures for the stable dressing of a wound, which is attributed to the inorganic/polymeric dual network and abundant coordination interactions between Ag@rGO nanosheets and PNIPAM. The biocompatibility and antibacterial ability against methicillin-resistant Staphylococcus aureus (MRSA) of this PEP-AG hydrogel wound dressing are confirmed in vitro and in vivo, which could transparently promote the healing of a MRSA-infected skin defect.
Graphite oxide, graphene, ZrO 2 -loaded graphene and b-Ni(OH) 2 -loaded graphene (joint appellation: Gs) were prepared and incorporated into polystyrene so as to improve the fire safety properties of polystyrene. By the masterbatch-melt blending technique, Gs nanolayers were well dispersed and exfoliated in polystyrene as thin layers (thickness 0.7-2 nm). The fire safety properties were visibly improved, including an increased thermal degradation temperature (18 C, PS/Ni-Gr-2), decreased peak heat release rate (40%, PS/Zr-Gr-2) and reduced CO concentration (54%, PS/Ni-Gr-2). The mechanism for the improved thermal stability and fire safety properties was investigated based on this study and previous works. The physical barrier effect of graphene, the interaction between graphene and polystyrene, and the synergistic effect of the metal compounds are the causes for the improvements.
In this work, molybdenum disulfide (MoS 2 )−modified graphene (MoS 2 /GNS) hybrids were prepared by the hydrothermal method and characterized by X-ray diffraction (XRD), Laser Raman spectroscopy (LRS) and transmission electron microscope (TEM). The characterization results show layered molybdenum disulfide was deposited on the surface of graphene nanosheets (GNSs) and grahene oxide was reduced simultaneously. Thermogravimetric analysis results of MoS 2 , GNS and MoS 2 /GNS hybrids showed that incorporation of MoS 2 increased the thermal oxidation resistance of the graphene evidently. Compared to pure epoxy resins (EP), the addition of MoS 2 /GNS hybrids into EP enhanced the onset thermal degradation temperature (T onset ) with an 53°C increment under air atmosphere and an 18°C increment under nitrogen atmosphere. The addition of MoS 2 /GNS hybrids endows excellent flame retardant properties to EP, confirmed by the dramatically reduced peak heat release rate value and total heat release value. Moreover, the addition of MoS 2 /GNS hybrids dramatically decreased the smoke products.
Nature has been inspiring scientists to fabricate impact protective materials for applications in various aspects. However, it is still challenging to integrate flexible, stiffness-changeable, and protective properties into a single polymer, although these merits are of great interest in many burgeoning areas. Herein, we report an impact-protective supramolecular polymeric material (SPM) with unique impact-hardening and reversible stiffness-switching characteristics by mimicking sea cucumber dermis. The emergence of softness−stiffness switchability and subsequent protective properties relies on the dynamic aggregation of the nanoscale hard segments in soft transient polymeric networks modulated by quadruple H-bonding. As such, we demonstrate that our SPM could efficiently reduce the impact force and increase the buffer time of the impact. Importantly, we elucidate the underlying mechanism behind the impact hardening and energy dissipation in our SPM. Based on these findings, we fabricate impact-and puncture-resistant demos to show the potential of our SPM for protective applications.
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