An extension of the classic thermodynamics theory to nanometer scale has generated a new interdisciplinary theory – nanothermodynamics. It serves as a bridge between macroscopic and nanoscopic ...systems. Over the past decade, nanothermodynamics theories have developed rapidly owing to their critical role in investigating the size-dependent physicochemical properties of nanomaterials. This review examines up-to-date research results on this cutting-edge topic. The focus and emphasis are on the utilization of nanothermodynamics models to investigate the size-dependent thermal stability, magnetic properties, photoelectric behaviors, thermoelectric phenomena, mechanical properties, electrical properties, etc. of nanomaterials.
A range of properties have been studied with respect to the effects of size, dimensionality and composition through a quantitative nanothermodynamics model. It is found that (a) the size dependence of these properties can be universally reconciled to the effect of severe bond dangling; (b) for the same material size, the sequence of size effects on the properties, from strong to weak, is nanoparticles, nanowires and thin films; and (c) the composition effects on the properties of nanoalloys are substantial, having a nonlinear relationship. It also reveals that vacancy formation determined by the cohesive energy variation is one of the intrinsic factors which dominate the size-dependent physicochemical properties of nanomaterials.
Design and development of smart sensors for rapid flame detection in postcombustion and early fire warning in precombustion situations are critically needed to improve the fire safety of combustible ...materials in many applications. Herein, we describe the fabrication of hierarchical coatings created by assembling a multilayered graphene oxide (GO)/silicone structure onto different combustible substrate materials. The resulting coatings exhibit distinct temperature-responsive electrical resistance change as efficient early warning sensors for detecting abnormal high environmental temperature, thus enabling fire prevention below the ignition temperature of combustible materials. After encountering a flame attack, we demonstrate extremely rapid flame detection response in 2–3 s and excellent flame self-extinguishing retardancy for the multilayered GO/silicone structure that can be synergistically transformed to a multiscale graphene/nanosilica protection layer. The hierarchical coatings developed are promising for fire prevention and protection applications in various critical fire risk and related perilous circumstances.
Lightweight polymer foam materials that are resilient and flame retardants are required in various practical applications. However, it has remained a great challenge to realize high-temperature ...resilience and flame resistance in polymer foams at an ultra-low loading of flame retardant additives. Herein we report a facile, low-cost and scalable strategy to create unprecedented high-performance polydimethylsiloxane foam materials by the in situ reactive self-assembly of graphene oxide (GO) sheets. Addition of 0.10 wt% GO produces compact and ultrathin protective nano-coatings on the foam surface. Moreover, such nano-coatings are chemically bonded with the foam skeleton. As a result, the nano-coatings produce significantly improved thermal stability and high-temperature resilience as well as synergistic fire shielding properties, enabling ∼57% and ∼87% reduction in the heat release rate and total smoke rate at 0.10 wt% and a limiting oxygen index of >31% at 0.50 wt%. By observing the burnt surface zones, we demonstrate that the thermal decomposition of PDMS molecules transforms them into inorganic nano-silica layers and promotes GO graphitization to form compact protective char, leading to synergetic flame retardant properties. The successful fabrication of the fascinating polymer foam materials provides new perspectives for the understanding and design of advanced polymer foam nanocomposite materials.
Epoxy composites filled with 2D chemically reduced graphene oxide (CRGO) sheets and preformed 3D powdered rubber (PR) nanoparticles were fabricated to investigate the effect of hybrid nanofillers on ...the electrical, thermal and mechanical properties as well as fracture toughness. As expected, the presence of CRGO sheets endows epoxy with electrical conductivity and enhances its thermal properties, stiffness and toughness; while the addition of PR results in significant reductions in thermal stability and stiffness, but produces dramatic improvements in fracture toughness. Compared with the binary composites, the ternary composites containing hybrid 2D CRGO and 3D PR fillers provide a good balance among electrical conductivity, thermal stability, glass transition temperature, stiffness, strength and fracture toughness, which cannot be achieved by independent single-phase fillers. Based on the morphologies of the fracture surfaces and damage zones around the crack tip, various toughening mechanisms such as crack-bridging by GO sheets, sheet/sheet delamination and sheet/matrix debonding, rubber cavitation and matrix shear banding, were identified and correlated with the fracture toughness of the hybrid composites studied. Results obtained disclosed suppression of deformation and/or cavitation of the PR nanoparticles after the incorporation of CRGO, which explained the moderate improvement in fracture toughness of the hybrid composites.
Superhydrophobic surfaces are imperative in flexible polymer foams for diverse applications; however, traditional surface coatings on soft skeletons are often fragile and can hardly endure severe ...deformation, making them unstable and highly susceptible to cyclic loadings. Therefore, it remains a great challenge to balance their mutual exclusiveness of mechanical robustness and surface water repellency on flexible substrates. Herein, we describe how robust superhydrophobic surfaces on soft poly(dimethylsiloxane) (PDMS) foams can be achieved using an extremely simple, ultrafast, and environmentally friendly flame scanning strategy. The ultrafast flame treatment (1–3 s) of PDMS foams produces microwavy and nanosilica rough structures bonded on the soft skeletons, forming robust superhydrophobic surfaces (i.e., water contact angles (WCAs) > 155° and water sliding angles (WSAs) < 5°). The rough surface can be effectively tailored by simply altering the flame scanning speed (2.5–15.0 cm/s) to adjust the thermal pyrolysis of the PDMS molecules. The optimized surfaces display reliable mechanical robustness and excellent water repellency even after 100 cycles of compression of 60% strain, stretching of 100% strain, and bending of 90° and hostile environmental conditions (including acid/salt/alkali conditions, high/low temperatures, UV aging, and harsh cyclic abrasion). Moreover, such flame-induced superhydrophobic surfaces are easily peeled off from ice and can be healable even after severe abrasion cycles. Clearly, the flame scanning strategy provides a facile and versatile approach for fabricating mechanically robust and surface superhydrophobic PDMS foam materials for applications in complex conditions.
The development of three-dimensional (3D) graphene nanoribbon (GNR) based porous composites with both mechanical reliability and multiple functionality has attracted great interest due to their ...promising applications in strain sensing, oil/water separation, etc. Herein, we report a facile strategy to fabricate robust porous 3D GNR wrapped polymer foam composites through modulating an interconnected GNR network and introducing a flexible polydimethylsiloxane (PDMS) coating. By simply adjusting the graphene oxide nanoribbon (GONR) concentration in aqueous solution followed by chemical reduction, the presence of the reduced GONR (rGONR) sheets endows commercial polyurethane (PU) foam with electrical conductivity without altering their porous microstructure. The mechanical properties of the rGONR-coated PU (PGR) foam composites depend strongly on the rGONR content and exhibit poor stability at low content due to the breakage of the rGONR network during cyclic deformation. Introduction of the flexible PDMS coating effectively stabilizes the 3D rGONR network on the foam skeleton, producing excellent mechanical reliability, e.g., reversible compressibility at a compressive strain of 80% for 100 cycles. Moreover, these mechanically stable and porous PDMS modified PGR composites display excellent lipophilic-hydrophobic behavior, which provides good oil/solvent absorption capacity and highly efficient continuous oil/water separation.
Graphene origami (G-ori) can possess unique mechanical properties and achieve some distinctive functionalization by engineering their configurations. However, it remains a tremendous challenge to ...modulate its formation and properties at the micro- and nano-scales. Herein, we systemically present the formation of G-ori activated by creased marks via molecular dynamics (MD) simulations. The pre-existing creased mark in graphene is created in a controlled way by transforming sp2 to sp3 bonds at the crease. Our results show that the presence of interlayer sp3 bonds at the crease can direct crack growth and hence pave a new way to tailor graphene sheets into specified pieces. The crease also guides the folding process of graphene into various geometric configurations. Sophisticated G-ori can be constructed by designing rational crease distribution on the graphene surface. Checking against the folding process of paper origami shows that the crease-induced targeted folding can be achieved at both nano- and macro-scales in exactly the same way. Our findings provide a simple and feasible method to construct graphene-based nano-devices by designing rational morphological configurations of G-ori.
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Lightweight, mechanically flexible and flame retardant polydimethylsiloxane (PDMS) foam materials modified with low content of nano-fillers are highly needed for versatile applications. Instead of ...the direct mechanical mixing technique that induced the embedment of nanofillers inside the matrix, herein, a facile, rapid and green restricted assembly strategy was established to prepare PDMS foam composites coated with an extremely low content of restricted graphene oxide (GO) sheets. A GO/water mixture in silicone oil emulsion was prepared to produce the restricted assembly of GO layers precisely and solely on the foam surface with no GO sheets inside the skeleton. Based on such restricted assembly induced by the amphiphilic surfactant molecules, the presence of only ∼0.04 wt% GO greatly improved the flame resistance (e.g., 40.6% reduction in heat release rate and 27.1% of limit oxygen index) of PDMS foams without affecting the low density (∼0.23 g/cm3) and mechanical flexibility (unchanged stress at strain 70% after 100 cycles under 200 °C). Observations and analysis of the burnt zones demonstrated that the restricted ultralow content GO sheets formed a compact protective layer facilitated by the pyrolysis of the PDMS molecules, thus protecting the inside of the PDMS material from the heat and oxygen attacks. These results confirmed that the restricted self-assembly of 2D nano-fillers approach is effective for the fabrication of flame-retardant PDMS foams and retention of other important properties.
Case reports of severe acute liver injury (ALI) following COVID-19 vaccination have recently been published. We evaluated the risks of ALI following COVID-19 vaccination (BNT162b2 or CoronaVac).
We ...conducted a modified self-controlled case series analysis using the vaccination records in Hong Kong with data linkage to electronic medical records from a territory-wide healthcare database. Incidence rate ratios (IRRs) for ALI outcome in the 56-day period following first and second doses of COVID-19 vaccines in comparison to the non-exposure period were estimated and compared to the ALI risk in patients with SARS-CoV-2 infection.
Among 2,343,288 COVID-19 vaccine recipients who were at risk, 4,677 patients developed ALI for the first time between 23rd February 2021 to 30th September 2021. The number of ALI cases within 56 days after the first and second dose of vaccination were 307 and 521 (335 and 334 per 100,000 person-years) for BNT162b2, and 304 and 474 (358 and 403 per 100,000 person-years) for CoronaVac, respectively, compared to 32,997 ALI cases per 100,000 person-years among patients within 56 days of SARS-CoV-2 infection. Compared to the non-exposure period, no increased risk was observed in the 56-day risk period for first (IRR 0.800; 95% CI 0.680–0.942) and second (IRR 0.944; 95% CI 0.816–1.091) dose of BNT162b2, or first (IRR 0.689; 95% CI 0.588–0.807) and second (IRR 0.905; 95% CI 0.781–1.048) dose of CoronaVac. There were no severe or fatal cases of ALI following COVID-19 vaccination.
There was no evidence of an increased risk of ALI associated with BNT162b2 or CoronaVac vaccination. Based on all current available evidence from previous studies and our study, the benefit of mass vaccination far outweighs the ALI risk from vaccination.
There have been some recent reports that COVID-19 vaccination could be associated with acute liver injury. In our study, we found no evidence that COVID-19 vaccination increased the risk of acute liver injury, which was much more common after SARS-CoV-2 infection than after vaccination. Hence, our study provides further data indicating that the benefits of mass COVID-19 vaccination outweigh the potential risks.
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•Incidence of acute liver injury following COVID-19 vaccination is very low and not increased compared to the non-exposure period.•Most post-vaccination acute liver injury was mild and self-limiting, with no increase in risk of new-onset chronic liver disease.•Acute liver injury is more common after SARS-CoV-2 infection than following COVID-19 vaccination.•The potential benefits of mass vaccination against COVID-19 outweigh the risk of liver injury from vaccination.
Hemophilia A is a rare bleeding disorder with variable expressivity and allelic heterogeneity. Despite the advancement of prenatal diagnostics and molecular studies, the number of studies reviewing ...the reproductive choices of hemophilia A carriers and affected individuals remains limited. Through this retrospective review, we hope to gain a deeper understanding of hemophilia A‐affected individuals' clinical and molecular characteristics, as well as the reproductive choices of the at‐risk couples. A total of 122 individuals harboring likely causative F8 gene alterations from 64 apparently unrelated families attending three centers between 3/2000 and 3/2023 were included in this study. Their clinical and molecular findings as well as reproductive choices were gathered in a clinical setting and verified through the electronic medical record database of the public health system. Forty‐seven affected males and 75 female heterozygous carriers were included in the analysis. Among 64 apparently unrelated families, 36 distinct pathogenic/likely pathogenic variants were identified, of which 30.6% (11/36) of variants were novel. While the majority of clinical findings and genotype–phenotype correlations appear to be in accordance with existing literature, female carriers who had no fertility intention were significantly more likely to have affected sons than those who had fertility intention (5/19 vs. 4/5; p = 0.047). Through this retrospective review, we summarized the clinical and molecular characteristics of 122 individuals harboring pathogenic/likely pathogenic F8 variants, as well as their fertility intentions and reproductive outcomes. Further studies are required to look into the considerations involved in reproductive decision‐making.
