Noncovalently Functionalized Tungsten Disulfide Nanosheets for Enhanced Mechanical and Thermal Properties of Epoxy Nanocomposites

Constructing Heterostructured MWCNT-BN Hybrid Fillers in Electrospun TPU Films to Achieve Superior Thermal Conductivity and Electrical Insulation Properties

The development of thermally conductive polymer/boron nitride (BN) composites with excellent electrically insulating properties is urgently demanded for electronic devices. However, the method of constructing an efficient thermally conductive network is still challenging. In the present work, heterostructured multi-walled carbon nanotube-boron nitride (MWCNT-BN) hybrids were easily prepared using an electrostatic self-assembly method. The thermally conductive network of the MWCNT-BN in the thermoplastic polyurethane (TPU) matrix was achieved by the electrospinning and stack-molding process. As a result, the in-plane thermal conductivity of TPU composite films reached 7.28 W m-1 K-1, an increase of 959.4% compared to pure TPU films. In addition, the Foygel model showed that the MWCNT-BN hybrid filler could largely decrease thermal resistance compared to that of BN filler and further reduce phonon scattering. Finally, the excellent electrically insulating properties (about 1012 Ω·cm) and superior flexibility of composite film make it a promising material in electronic equipment. This work offers a new idea for designing BN-based hybrids, which have broad prospects in preparing thermally conductive composites for further practical thermal management fields.

Mechanical reinforcement from two-dimensional nanofillers: model, bulk and hybrid polymer nanocomposites

Thanks to their intrinsic properties, multifunctionality and unique geometrical features, two-dimensional nanomaterials have been used widely as reinforcements in polymer nanocomposites. The effective mechanical reinforcement of polymers is, however, a multifaceted problem as it depends not only on the intrinsic properties of the fillers and the matrix, but also upon a number of other important parameters. These parameters include the processing method, the interfacial properties, the aspect ratio, defects, orientation, agglomeration and volume fraction of the fillers. In this review, we summarize recent advances in the mechanical reinforcement of polymer nanocomposites from two-dimensional nanofillers with an emphasis on the mechanisms of reinforcement. Model, bulk and hybrid polymer nanocomposites are reviewed comprehensively. The use of Raman and photoluminescence spectroscopies is examined in light of the distinctive information they can yield upon stress transfer at interfaces. It is shown that the very diverse family of 2D nanofillers includes a number of materials that can attribute distrinctive features to a polymeric matrix, and we focus on the mechanical properties of both graphene and some of the most important 2D materials beyond graphene, including boron nitride, molybdenum disulphide, other transition metal dichalcogenides, MXenes and black phosphorous. In the first part of the review we evaluate the mechanical properties of 2D nanoplatelets in "model" nanocomposites. Next we examine how the performance of these materials can be optimised in bulk nanocomposites. Finally, combinations of these 2D nanofillers with other 2D nanomaterials or with nanofillers of other dimensions are assessed thoroughly, as such combinations can lead to additive or even synergistic mechanical effects. Existing unsolved problems and future perspectives are discussed.

Generalized ratiometric surface-enhanced Raman scattering biosensor for okadaic acid in food based on Au-triggered signal amplification

BACKGROUND

Reliability and robustness have been recognized as key challenges for Surface-enhanced Raman scattering (SERS) analytical techniques. Quantifying the concentration of an analyte using a single characteristic peak from SERS has been a controversial topic because the Raman signal is susceptible to highly concentrated electromagnetic hotspots, inhomogeneity of SERS substrate, or non-standardization of measurement conditions. Ratiometric SERS strategies have been demonstrated as a promising solution to effectively balance and compensate for signal fluctuations caused by matrix heterogeneity. However, it is not easy to construct ratiometric SERS sensors with monitoring the ratio of two different signal intensities for target analysis.

RESULTS

An attempt has been made to develop a novel ratiometric biosensor that can be applied to detect okadaic acid (OA). Aptamer-anchored magnetic particles were first combined with gold-tagged short complementary DNA (Au-cDNA) to create heterogeneous nanostructures. When the target was present, the Au-cDNA was dissociated from nanostructures, and 4-nitrothiophenol (4-NTP) was initiated to reduce to 4-aminothiophenol (4-ATP) in the presence of hydrogen sources. The SERS ratio change of 4-NTP and 4-ATP was finally detected by AuNPs-coated film. OA was successfully quantified, and the detection limit was as low as 2.4524 ng/mL. The constructed biosensor had good stability and reproducibility with a relative standard deviation of less than 4.47%. The proposed method used gold nanoparticles as an intermediate to achieve catalytic signal amplification and subsequently increased the sensitivity of the biosensor.

SIGNIFICANCE AND NOVELTY

Catalytic reaction-based ratiometric SERS biosensors combine the multiple advantages of catalytic signal amplification and signal self-calibration and provide new insights into the development of stable, reproducible, and reliable SERS detection techniques. This ratiometric SERS technique offered a universal method that is anticipated to be applicable for the detection of other targets by substituting the aptamer.

Casein-assisted exfoliation of tungsten disulfide nanosheets for biomedical applications

Our regular life can be more challenging by bone abnormalities. Bone tissue engineering is used for repairing, regenerating, or replacing bone tissue that has been injured or infected. It is effective in overcoming the drawbacks of conventional bone grafting methods like autograft and allograft by enhancing the effectiveness of bone regeneration. Recent discoveries have shown that the exfoliation of transition metal dichalcogenides (TMDs) with protein is in great demand for bone tissue engineering applications. WS2 nanosheets were developed using casein and subsequently characterized with different analytical techniques. Strong absorption peaks were observed in the UV-visible spectra at 520 nm and 630 nm. Alginate and alginate-casein WS2 microspheres were developed. Stereomicroscopic images of the microspheres are spherical in shape and have an average diameter of around 0.8 ± 0.2 mm. The alginate-casein WS2 microspheres show higher content of water absorption and retention properties than only alginate-containing microspheres. The apatite formation in the simulated bodily fluid solution was facilitated more effectively by the alginate-casein-WS2 microspheres. Additionally, alginate-casein-WS2 microspheres have a compressive strength is 58.01 ± 4 MPa. Finally, in vitro cell interaction studies reveals that both the microspheres are biocompatible with the C3H10T1/2 cells, and alginate-casein-WS2-based microspheres promote cell growth more significantly. Alginate-casein-WS2 microspheres promote alkaline phosphatase activity, and mineralization process. Additionally, alginate-casein-WS2-based microspheres exponentially enhance the genes for ALP, BMP-2, OCN, and Collage type-1. The produced alginate-casein-WS2 microspheres could be a suitable synthetic graft for a bone transplant replacement.

Improving Fracture Toughness of Tetrafunctional Epoxy with Functionalized 2D Molybdenum Disulfide Nanosheets

In this work, improved fracture toughness of tetra-functional epoxy polymer was obtained using two-dimensional (2H polytype) molybdenum disulfide (MoS2) nano-platelets as a filler. Simultaneous in-situ exfoliation and functionalization of MoS2 were achieved in the presence of cetyltrimethylammonium bromide (CTAB) via sonication. The aim was to improve the dispersion of MoS2 nanoplatelets in epoxy and enhance the interfacial interaction between nanoplatelets and epoxy matrix. Epoxy nanocomposites with CTAB functionalized MoS2 (f-MoS2) nanoplatelets, ranging in content from 0.1 wt% up to 1 wt%, were fabricated. Modified MoS2 improved the fracture properties (81%) of tetrafunctional epoxy nanocomposites. The flexural strength and compressive strength improved by 64% and 47%, respectively, with 0.25 wt% loading of f-MoS2 nanoplatelets compared to neat epoxy. The addition of f-MoS2 nanoplatelets enhanced the thermomechanical properties of epoxy. This work demonstrated the potential of organically modified MoS2 nanoplatelets for improving the fracture and thermal behavior of tetrafunctional epoxy nanocomposites.

Near-infrared light responsive dendrimers facilitate the extraction of bicalutamide from human plasma and urine

BACKGROUND

Today, it is well accepted that the quantitative measurement of anti-cancer drugs in human biological samples requires the development and validation of efficient bioanalytical methods. This study attempts to provide a high-capacity and thermo-sensitive nano-adsorbent for bicalutamide extraction from human biological fluids.

MAIN METHODS AND MAJOR RESULTS

In this study, five generations of thermo-sensitive dendrimers were synthesized onto the surface of WS₂ nano-sheets. After drug-loading process from body fluids, the near-infrared (NIR) light (at 808 nm) was applied and light-to-heat conversion by the WS₂ nano-sheets led to shrinkage in polymer chains, resulting the release of the entrapped drug. Finally, the extracted drug was analyzed via HPLC-UV system (at 270 nm). The final nano-adsorbent was described via FE-SEM, XRD, FT-IR, and TGA techniques. The adsorption isotherm data were well fitted by Langmuier isotherm model (R²  = 0.9978). The mean recoveries for spiking bicalutamide at three different concentrations in plasma and urine samples were 92.12% and 94.54% under the NIR light irradiation.

CONCLUSIONS AND IMPLICATIONS

We have developed a smart strategy to analyze bicalutamide in biological samples using near-infrared light irradiation in a controlled manner. All the results indicate the promising application of the proposed method for the extraction and determination of bicalutamide.

Mechanical properties of aerospace epoxy composites reinforced with 2D nano-fillers: current status and road to industrialization

High-performance epoxy composites find application in the aerospace industry. Although epoxy is a high-performance polymer, its fracture toughness is compromised due to its highly cross-linked nature. Nanomaterials such as carbon nanotubes (CNTs), graphene derivatives, and inorganic 2-dimensional (2D) nanomaterials are being explored to improve epoxy composites' mechanical properties. Graphene is one of the most popular 2D nano-reinforcing agents for epoxy composites. Following graphene discovery, the research community's attention was brought to various other few-atom thick 2D nanomaterials. Hence, apart from graphene, inorganic nanosheets such as transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), etc., are also being studied as modifiers for enhancing the mechanical performance of epoxy composites. Graphene, TMDs and hBN are known to possess a high aspect ratio, high specific surface area and inherently high mechanical strength and stiffness, contributing to a stronger and tougher composite. Despite that, the challenges associated with these nanomaterials, such as dispersion issues, lack of standardization, underlying health hazards, etc., have hampered their commercialization. It has been long past a decade since the discovery of graphene, yet there are concerns regarding the lab to industry scale-up, and health and environmental hazards associated with nanomaterials for the fabrication of aerospace composites. This review offers a comprehensive literature survey and a perspective into the possible ways of bridging the gaps between the laboratory research and industrialization of 2D nanosheet-filled epoxy composites.

Nacre-Inspired Strong and Multifunctional Soy Protein-Based Nanocomposite Materials for Easy Heat-Dissipative Mobile Phone Shell

Inspired by the hierarchically ordered "brick and mortar" (BM) architecture of natural nacre, in this study a rational assembly of boron nitride (BN) nanosheets was introduced into a mixture of trimethylolpropane triglycidyl ether (TTE) and soy protein isolate (SPI), and a strong and multifunctional SPI-based nanocomposite film with multinetwork structure was synthesized. At a low BN loading (<0.5%), the resulting multifunctional film was flexible, antiultraviolet, and nearly transparent and also displayed good thermal diffusion ability and exhibited an excellent combination of high tensile strength (36.4 MPa) and thermal conductivity (TC, 2.40 W·m^-1·K^-1), surpassing the performances of various types of petroleum-based plastics (displayed a tensile strength ranging from 1.9 to 21 MPa and TC ranging from 0.55-2.13 W·m^-1·K^-1), including nine different types of materials currently utilized for mobile phone shells, suggesting its vast potential in practical applications.

Polymer Ligand Design and Surface Modification of Ag Nanowires toward Color-Tone-Tunable Transparent Conductive Films

Ag nanowire suspensions are one of the indispensable materials in the design and fabrication of flexible transparent conductive films. Although the required properties of Ag nanowire films, such as their high transparency, low haze, low contact resistance, and suppression of yellowing, are strongly related to the nanowire surface phenomena, approaches for the surface modification of polyol-synthesized Ag nanowires have rarely been reported. Here, we report the design of a polymer ligand and surface modification of Ag nanowires with the designed polymer to obtain color-tunable transparent conductive films through a simple casting and drying process. In this approach, we synthesized a series of functional polymer ligands by partially grafting polyethyleneimine (PEI) with polyethylene glycol (PEG) chains (PEI-mPEG). The amine sites in PEI-mPEG were designed to act as adsorption sites as well as anchoring sites for an anionic blue dye for suppressing the yellow color tone of Ag nanowires. On the other hand, the PEG chains were designed to maintain the stability of the Ag nanowires in aqueous suspensions and to suppress corrosion of Ag nanowires, which is enhanced by the amine groups of PEI. The effect of the grafting ratio of PEG chains on PEI on the ligand-exchange behavior of the Ag nanowires, their dispersion stability in aqueous inks, and final film properties were investigated systematically. Furthermore, successful color tuning of the Ag nanowire film, without suppressing the conductive and optical properties, is demonstrated by loading anionic blue dye onto PEI-mPEG-modified Ag nanowires.

Engineering WS2–Au–HRP-assisted multiple signal amplification strategy for chemiluminescence immunoassay of prostate specific antigen

Engineering of a WS₂–Au–HRP-assisted multiple signal amplification strategy for CL immunoassay of PSA.

Large-scale surfactant-free synthesis of WS2 nanosheets: an investigation into the detailed reaction chemistry of colloidal precipitation and their application as an anode material for lithium-ion and sodium-ion batteries

Novel detailed chemistry of WS₂ synthesis.

A Hydrothermal-Assisted Ball Milling Approach for Scalable Production of High-Quality Functionalized MoS2 Nanosheets for Polymer Nanocomposites

The most known analogue of graphene, molybdenum disulfide (MoS₂) nanosheet, has recently captured great interest because it can present properties beyond graphene in several high technological applications. Nonetheless, the lack of a feasible, sustainable, and scalable approach, in which synthesizing and functionalization of 2H-MoS₂ nanosheets occur simultaneously, is still a challenge. Herein, a hydrothermal treatment has been utilised to reduce the effect of breaking mechanisms on the lateral size of produced nanosheets during the ball milling process. It was demonstrated that the hydrothermal pre-treatment led to the initial intercalation of an organic molecule such as 4,4′-diaminodiphenyl sulfone (DDS) within the stacked MoS₂ sheets. Such a phenomenon can promote the horizontal shear forces and cause sliding and peeling mechanisms to be the dominated ones during low energy ball milling. Such combined methods can result in the production of 2H functionalized MoS₂ nanosheets. The resultant few layers showed an average lateral dimension of more than 640 nm with the thickness as low as ~6 nm and a surface area as high as ~121.8 m²/g. These features of the synthesised MoS₂ nanosheets, alongside their functional groups, can result in fully harnessing the reinforcing potential of MoS₂ nanosheets for improvement of mechanical properties in different types of polymeric matrices.

Room-Temperature Delayed Fluorescence of Gold Nanoclusters in Zinc-Mediated Two-Dimensional Crystalline Assembly

We report that complexation-reaction-mediated two-dimensional crystalline assembly of gold (Au₁₄) nanoclusters (NCs) exhibits room-temperature delayed fluorescence at 605 nm, with an unprecedented long lifetime of 0.5 ms and an exceptionally high quantum yield of 19.1 ± 0.9%. Interestingly, the as-synthesized Au NCs had a very weak delayed fluorescence signal. The enhancement in delayed fluorescence of Au NCs upon formation of assembly has been attributed to the crystallization-induced structural rigidity, which restricted the nonradiative transitions and enhanced the excited-state lifetime. The attainment of crystalline organization was substantiated by electron diffraction analysis. A possible structure was established based on experimental results and computational optimizations. Atomic force microscopy revealed the formation of multilayered two-dimensional nanosheets with thickness of 2.44 ± 0.48 nm.

Nanocomposite of Poly(l-Lactic Acid) with Inorganic Nanotubes of WS2

Composites of poly(l-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT–WS2) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly d,l-lactic acid (PDLLA) and others were considered in combination with the INT–WS2. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS2 nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.

Amino Functionalization of Reduced Graphene Oxide/Tungsten Disulfide Hybrids and Their Bismaleimide Composites with Enhanced Mechanical Properties

A novel graphene-based nanocomposite particles (NH₂-rGO/WS₂), composed of reduced graphene oxide (rGO) and tungsten disulfide (WS₂) grafted with active amino groups (NH₂-rGO/WS₂), was successfully synthesized by an effective and facile method. NH₂-rGO/WS₂ nanoparticles were then used to fabricate new bismaleimide (BMI) composites (NH₂-rGO/WS₂/BMI) via a casting method. The results demonstrated that a suitable amount of NH₂-rGO/WS₂ nanoparticles significantly improved the mechanical properties of the BMI resin. When the loading of NH₂-rGO/WS₂ was only 0.6 wt %, the impact and flexural strength of the composites increased by 91.3% and 62.6%, respectively, compared to the neat BMI resin. Rare studies have reported such tremendous enhancements on the mechanical properties of the BMI resin with trace amounts of fillers. This is attributable to the unique layered structure of NH₂-rGO/WS₂ nanoparticles, fine interfacial adhesion, and uniform dispersion of NH₂-rGO/WS₂ in the BMI resin. Besides, the thermal gravimetrical analysis (TGA) revealed that the addition of NH₂-rGO/WS₂ could also improve the stability of the composites.

Recent advances in the field of transition metal dichalcogenides for biomedical applications

Nanosheets of transition metal dichalcogenide (TMDs), the graphene-like two-dimensional (2D) materials, exhibit a unique combination of properties and have attracted enormous research interest for a wide range of applications including catalysis, functional electronics, solid lubrication, photovoltaics, energy materials and most recently in biomedical applications. Their potential for use in biosensors, drug delivery, multimodal imaging, antimicrobial agents and tissue engineering is being actively studied. However, the commercial translation of exfoliated TMDs has been limited due to the low aqueous solubility, non-uniformity, lack of control over the layer thickness, and the long-term colloidal stability of the exfoliated material. There is wide interest in the synthesis and exfoliation of TMDs resulting in the reporting of increasing numbers of new methods and their biomedical applications. The unique physicochemical characteristics of the TMD nanosheets have been exploited to tether them with biological payload to achieve selective localized delivery in vivo. The large surface-to-volume ratio, good cytocompatibility, ease of surface modification, tunable bandgap, strong spin-orbit coupling, and high optical and thermal conversion efficiency of TMD nanosheets make them favorable over traditional nanomaterials for biomedical research. Moreover, the presence of abundant active edge sites on the 2D TMDs makes them suitable for catalytic activities, while the large surface area and the interspace between layers are particularly conducive to ion or small molecule intercalation, making them useful for energy storage applications with rapid redox reaction capabilities. One of the major limitations of the exfoliated TMDs has been their limited colloidal stability in aqueous media. In this review, we summarize the recent advances in the exfoliation and synthesis of single-layered TMDs, their biomedical efficacy in terms of cytotoxicity, combinatorial therapy and diagnostic imaging, as well as antimicrobial activity. We highlight the current challenges in the field and propose strategies for the future.

Hybrid nanocomposites of 2D black phosphorus nanosheets encapsulated in PMMA polymer material: new platforms for advanced device fabrication

Hybrid materials, containing a 2D filler embedded in a polymeric matrix, are an interesting platform for several applications, because of the variety of properties that the filler can impart to the polymer matrix when dispersed at the nanoscale. Moreover, novel properties could arise from the interaction between the two. Mostly the bulk properties of these materials have been studied so far, especially focusing on how the filler changes the polymeric matrix properties. Here we propose a complete change of perspective by using the hybrid nanocomposite material as a platform suitable to engineer the properties of the filler and to exploit its potential in the fabrication of devices. As a proof of concept of the versatility and the potential of the new method, we applied this approach to prepare black phosphorus (bP) nanocomposites through its dispersion in poly (methyl methacrylate). bP is a very interesting 2D material, whose application have so far been limited by its high reactivity to oxygen and water. In this respect, we show that electronic-grade bP flakes, already embedded in a protecting matrix since their exfoliation from the bulk material, are endowed with significantly increased stability and can be further processed into devices without degrading their properties.

Study on the flammability, thermal stability and diffusivity of polyethylene nanocomposites containing few layered tungsten disulfide (WS2) functionalized with metal oxides

In this work, exfoliated tungsten disulfide (WS2) functionalized with metal oxides as a filler of polyethylene (PE) was used. An efficient exfoliation procedure resulted in the synthesis of 7-9 layered flakes of WS2. Flakes of exfoliated WS2 were functionalized by iron oxide and nickel oxide nanoparticles, respectively. The nanomaterials were mixed with polyethylene by extrusion. Methods such as Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) or Thermogravimetric Analysis (TGA) were used to characterize the materials. Flame retardant properties were investigated by microcalorimetry. Comparing the obtained values of heat released during combustion, it can be observed that the addition of fillers reduces flammability significantly compared to neat polyethylene. It is revealed that this composite can provide a certain physical barrier and inhibit the diffusion of heat and gaseous products during combustion. Thermogravimetric analysis of composites showed increased thermal stability with addition of nanofillers and reduction of carbon monoxide generation in the whole range of the nanofiller addition (from 0.5 to 2 wt% in PE). Results suggested that the composite with Ni2O3 could endow the best flame retardance for PE. The peak heat release rate of this sample with 2 wt% nanofiller was reduced to 792 W g-1 (1216 W g-1 for PE), and the total heat release was decreased to 39 kJ g-1 (47 kJ g-1 for PE). A very significant increase in thermal conductivity for all composites was observed as well.

In situ growth of 0D silica nanospheres on 2D molybdenum disulfide nanosheets: Towards reducing fire hazards of epoxy resin

This report described a facile process for the preparation of 2D/0D MoS₂-SiO₂ hybrids using a simple in situ growth method, with the purpose of promoting the dispersion of MoS₂ in polymer matrices and improving the properties of polymer materials. FTIR, XPS, TGA and TEM measurements were performed to characterize the structure and morphology of the synthesized hybrids which were then introduced into epoxy to reduce flammability. The hybrids dispersed well in the epoxy matrix. No obvious agglomerations were observed. In comparison with those of neat epoxy, the incorporation of a low loading of MoS₂-SiO₂ hybrids resulted in significant decrements in heat release rate, total heat release and volume of toxic effluents released during combustion, which indicated that the fire hazards of epoxy composites were strongly reduced. The good dispersion, labyrinth barrier effect and the catalytic effect of MoS₂-SiO₂ hybrids on char formation may contribute to the observed decrease in the flammability of epoxy resin.