Development of NIR light-responsive shape memory composites based on bio-benzoxazine/bio-urethane copolymers reinforced with graphene

In this work, shape memory polymers (SMPs) were developed from a combination of a bio-based benzoxazine (BZ) monomer and polyurethane prepolymer (PU-prepolymer), both derived from bio-based raw materials. The bio-based BZ monomer (V-fa monomer) was synthesized through a Mannich condensation reaction using vanillin, paraformaldehyde, and furfurylamine. The bio-based PU-prepolymer was obtained by reacting palm oil polyol (MW = 1400 Da) and toluene diisocyanate (TDI). To investigate the curing behavior of poly(V-fa/urethane), with a mass ratio of 50/50, differential scanning calorimetry was employed. The structure of the resulting poly(V-fa/urethane) was confirmed using Fourier transform infrared spectroscopy. Furthermore, the synthesized V-fa/urethane copolymers with weight ratios of 70/30, 60/40, 50/50 and 40/60 were observed to exhibit shape memory behaviors induced by near-infrared irradiation (808 nm). Poly(V-fa/urethane), specifically with a mass ratio of 50/50, demonstrated superior shape memory performance. It exhibited a remarkable capacity to retain the temporary shape up to 90%, achieve 99% shape recovery, and exhibit a recovery time of 25 s. The shape memory properties were further improved with the addition of 3 wt% graphene nanoplatelets (GNPs), exhibiting an improvement in the shape fixity value to 94%, and shape recovery time value to 16 s. Moreover, our findings suggest that 60/40 poly(V-fa/urethane) reinforced with 3 wt% GNPs possesses favorable characteristics for applications as multiple SMPs, with shape fixity values of 97% and 94%, and shape recovery values of 96% and 89% for the first and second shapes, respectively.

Stable polyethylene glycol/biochar composite as a cost-effective photothermal absorber for 24 hours of steam and electricity cogeneration

Seawater desalination powered by solar energy is the most environmentally and economical solution in responding to the global water and energy crisis. However, solar desalination has been negatively impacted by intermittent sun radiation that alternates between day and night. In this study, sugarcane bagasse (SCB) was recycled via the pyrolysis process to biochar as a cost-effective solar absorber. Besides, polyethylene glycol (PEG) as a phase change material was encapsulated in the abundant pore structure of biochar to store the thermal energy for 24 hours of continuous steam generation. The BDB/1.5 PEG evaporator exhibited an evaporation rate of 2.11 kg m-2 h-1 (98.1% efficiency) under 1 sun irradiation. Additionally, the BDB/1.5 PEG evaporator incorporated by the TEC1-12706 module for continuous steam and electricity generation with a power density of 320.41 mW m-2. Moreover, 10 continuous hours of evaporation were applied to the composite demonstrating outstanding stability. The composite exhibited high water purification efficiency through solar desalination due to the abundant functional groups on the biochar surface. Finally, the resulting low-cost and highly efficient PCM-based absorber can be used on a wide scale to produce fresh water and energy.

Ultrasensitive Gas Detection Based on Electrically Enhanced Nanoplasmonic Sensor with Graphene-Encased Gold Nanorod

Nanoplasmonic sensors are a widely known concept and have been studied with various applications. Among them, gas detection is engaging attention in many fields. However, the analysis performance of nanoplasmonic sensors based on refractive index confined to the metal nanostructure characteristics causes challenges in gas detection. In this study, we develop a graphene-encased gold nanorod (AuNR)-based nanoplasmonic sensor to detect cadaverine gas. The graphene-encased AuNR (Gr@AuNR) presents an ultrasensitive peak wavelength shift even with tiny molecules. In addition, the external potential transmitted through graphene induces an additional shift. A chemical receptor is immobilized on Gr@AuNR (CR@Gr@AuNR) for selectively capturing cadaverine. The CR@Gr@AuNR achieves ultrasensitive detection of cadaverine gas, and the detection limit is increased to 15.99 ppb by applying a voltage to graphene. Furthermore, the experimental results of measuring cadaverine generated from spoiled pork show the practicality of CR@Gr@AuNR. The strategy of external-boosted nanoplasmonics provides new insight into plasmonic sensing and applications.

A step forward to overcome the cytotoxicity of graphene oxide through decoration with tragacanth gum polysaccharide

Hybridization of nanomaterials (NMs) with natural polymers is one of the best techniques to promote their exciting properties. In this way, the main objective of this work was to investigate the efficiency of decoration of the graphene oxide (GO) nano-sheets with tragacanth gum (TG) polysaccharide. To aim this, different approaches were used (with and without ultrasonic treatment) and various tests (XRD, FTIR, Raman, UV-Vis, DLS, Zeta potential, contact angle, AFM, FE-SEM, TEM, and MTT assay) were conducted. Test results indicated that the nano-hybrids were successfully synthesized. Furthermore, our findings represented that, the TG hybridized GO (TG-GO) appreciably enhanced the biocompatibility of GO. Moreover, it was demonstrated that the ultrasonic treatment of TG solution put a remarkable impact on the microstructure, wettability, and also surface charge characteristic of fabricated nano-hybrids and consequently improved the biocompatibility against L929-fibroblast cells.

Structure/Properties Relationship of Anionically Synthesized Diblock Copolymers "Grafted to" Chemically Modified Graphene

A novel approach to obtaining nanocomposite materials using anionic sequential polymerization and post-synthetic esterification reactions with chemically modified graphene sheets (CMGs) is reported. The anionically synthesized diblock copolymer precursors of the PS-b-PI-OH type were grafted to the chemically modified –COOH groups of the CMGs, giving rise to the final composite materials, namely polystyrene-b-poly(isoprene)-g-CMGs, which exhibited enhanced physicochemical properties. The successful synthesis was determined through multiple molecular characterization techniques together with thermogravimetric analysis for the verification of increased thermal stability, and the structure/properties relationship was justified through transmission electron microscopy. Furthermore, the arrangement of CMGs utilizing lamellar and cylindrical morphologies was studied in order to determine the effect of the loaded CMGs in the adopted topologies.

Three-dimensional Ag2S cubes for switchable multi-wavelength ultrashort pulse application

Three-dimensional (3D) materials are widely used in optoelectronics, thermodynamics and ultrafast fiber lasers because of their excellent nonlinear optical properties. Silver sulfide (Ag₂S) is a kind of 3D material with a unique cubic structure and large absorption coefficient. In this paper, a double-balance detection system is used to measure the saturation absorption intensity of Ag₂S as 226.6 MW cm^-2and the modulation depth as 13.9%. In the ring fiber laser, Ag₂S is used as a saturable absorber (SA) to obtain a stable dual-wavelength mode locking. The center wavelengths of the mode locking are 1536.9 and 1544.5 nm, and the corresponding 3 dB bandwidths are 1.3 and 1.5. nm. By adjusting the polarization controller, a tuning process from two wavelengths to multiple wavelengths is realized, and the tunable width is 13.1 nm. This phenomenon is due to the combined effect of birefringence and nonlinear effects in the cavity. To our knowledge, this is the first report of a multiplexed fiber laser with Ag₂S as a SA. The emergence of this result provides a valuable reference information for the multifunctional compact fiber laser, and the formed system can be applied in the fields of fiber sensing, telecommunications and optical communication.

Metal-Free Antibacterial Additives Based on Graphene Materials and Salicylic Acid: From the Bench to Fabric Applications

The custom functionalization of a graphene surface allows access to engineered nanomaterials with improved colloidal stability and tailored specific properties, which are available to be employed in a wide range of applications ranging from materials to life science. The high surface area and their intrinsic physical and biological properties make reduced graphene oxide and graphene oxide unique materials for the custom functionalization with bioactive molecules by exploiting different surface chemistries. In this work, preparation (on the gram scale) of reduced graphene oxide and graphene oxide derivatives functionalized with the well-known antibacterial agent salicylic acid is reported. The salicylic acid functionalities offered a stable colloidal dispersion and, in addition, homogeneous absorption on a sample of textile manufacture (i.e., cotton fabrics), as shown by a Raman spectroscopy study, thus providing nanoengineered materials with significant antibacterial activity toward different strains of microorganisms. Surprisingly, graphene surface functionalization also ensured resistance to detergent washing treatments as verified on a model system using the quartz crystal microbalance technique. Therefore, our findings paved the way for the development of antibacterial additives for cotton fabrics in the absence of metal components, thus limiting undesirable side effects.

Synthesis and characterization of graphene oxide chitosan aerogels reinforced with flavan-3-ols as hemostatic agents

The natural mechanisms of the body cannot control massive hemorrhaging, resulting in a requirement for hemostatic intervention. In this study, Graphene oxide and Chitosan aerogels reinforced with grape seed (SD) and skin (SK) extracts were developed for use as hemostatic agents by evaluating the influence of pH on their synthesis, and the amount of grape extract added on the physical and chemical properties of the aerogels. The material was evaluated by FTIR, XRD, Raman spectroscopy, DLS, uniaxial compression tests and SEM. The capacity of the aerogels to absorb water, PBS and blood, as well as their coagulation capacity, were determined. In addition, the release profile for grape extracts in PBS and the material's cytotoxicity were determined. The aerogels that were synthesized under basic conditions and loaded with grape extracts were more rigid and negatively charged, and they presented smaller pores than the un-loaded acidic aerogels. For all aerogels, the hemoglobin absorption was greater than 90 % in the first 30 s. A higher density of adsorbed blood cells was observed on aerogels loaded with a higher amount of grape extract. The maximum release of extract from the aerogels occurred for those loaded with SK extracts at a basic pH; the aerogels that were prepared under acidic conditions dissolved in the media. Aerogels loaded with SK extracts under alkaline conditions were not cytotoxic toward human dermal fibroblasts and exhibited cell viabilities above 90 %. These findings suggest that these aerogels have the potential for use as hemostatic agents in wound management.

Diazonium Modification of Inorganic and Organic Fillers for the Design of Robust Composites: A Review

This review focuses on fillers modified with diazonium salts and their use in composites. We reviewed scientific publications and presented information about such diazonium-modified fillers as boron nitride, carbon fillers, cellulose, clay, silica, titanium dioxide, and zeolite. The fillers were divided into two groups. The first group includes those that form covalent bonds with the polymer, while the second includes those that do not form them. This review indicates a tremendous impact of filler modification using diazonium salts on the properties of composites. The review presents examples of the impact of filler on such properties as thermal conductivity, thermal stability, and mechanical properties (e.g., interfacial shear strength, compressive strength, flexural strength). The presented review indicates the enormous potential of composites with diazonium-modified fillers in control drug release, antistatic coatings, electrode materials, photocatalysts, bone tissue engineering scaffolds, fuel cell applications, abrasive tools, and electromechanical strain sensor. We hope that this review will help both research groups and industry in choosing fillers for given types of polymers and obtaining composites with even better properties.

Enhanced Mechanical Properties of Multiscale Carbon Fiber/Epoxy Unidirectional Composites with Different Dimensional Carbon Nanofillers

Ammonia modified graphene-carbon nanotubes/continuous carbon fiber reinforced epoxy unidirectional multiscale composites (AMGNS-MWCNT/CFEP) were prepared by adding ammonia modified graphene and carbon nanotubes to an epoxy matrix to reduce agglomeration of carbon nanofillers in the epoxy matrix and improve composites properties. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and universal testing machines were used to characterize the properties of carbon nanofillers, AMGNS-MWCNT/epoxy nanocomposites, and AMGNS-MWCNT/CFEP unidirectional composites. When the AMGNS-MWCNT content was 1.0 wt%, flexural strength, the flexural modulus and interlaminar shear strength of AMGNS-MWCNT/CFEP unidirectional composites reached the maximum value of 1520.3 MPa, 138.88 GPa, and 87.80 MPa, respectively, which were 12.5%, 9.42%, and 10.1% higher than that of carbon fiber reinforced epoxy unidirectional composites (CFEP). The synergistic mechanism of two carbon nanofillers in the matrix is discussed.

Effect of Varying Amine Functionalities on CO2 Capture of Carboxylated Graphene Oxide-Based Cryogels

Graphene cryogels synthesis is reported by amine modification of carboxylated graphene oxide via aqueous carbodiimide chemistry. The effect of the amine type on the formation of the cryogels and their properties is presented. In this respect, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), were selected. The obtained cryogels were characterized by Fourier Transformed Infrared spectroscopy, thermogravimetric analysis, X-ray spectroscopy, and Scanning electron microscopy. The CO2 adsorption performance was evaluated as a function of amine modification. The results showed the best CO2 adsorption performance was exhibited by ethylenediamine modified aerogel, reaching 2 mmol g-1 at 1 bar and 298 K. While the total N content of the cryogels increased with increasing amine groups, the nitrogen configuration and contributions were determined to have more important influence on the adsorption properties. It is also revealed that the residual oxygen functionalities in the obtained cryogels represent another paramount factor to take into account for improving the CO2 capture properties of amine-modified graphene oxide (GO)-based cryogels.

Self-Assembled Graphene Composites for Flow-Through Filtration

Spontaneously exfoliated pristine graphene is used as a surfactant to template the formation of electrically conductive filters for the adsorption of an organic dye from water. In contrast to other reported graphene-based adsorption materials, our system provides a continuous approach to water treatment rather than a batch approach, and uses pristine graphene instead of the more costly and environmentally challenging graphene oxide. The use of self-assembled graphene also results in our filters being electrically conductive, providing a convenient route to clean the filters by resistive heating. An investigation of the mechanism of formation and filtration by these filters, templated by self-assembled two-dimensional pristine graphene, is presented. The thermodynamically driven exfoliation of natural flake graphite at a high-energy monomer/water interface produces water-in-oil emulsions stabilized by a thin layer of overlapping graphene sheets. Subsequent polymerization of the continuous monomer phase produces polymer foams with cells lined by graphene. With a combination of acoustic spectroscopy and electron microscopy, the effects of graphite concentration and temperature are studied, as is the correlation between droplet size and the size of the cells in the final polymer foam.

Thermal Property Studies of In Situ Blended Graphene/Nature Rubber Nanocomposites

In this work, graphene/nature rubber (GE/NR) composites with filler content from 0 wt% to 1 wt% were prepared by an in situ reduction process. Thermal properties of the nanocomposites were studied by thermogravimetric (TG) analysis and thermogravimetric difference (ΔTG). Composites with higher GE content evidenced stronger thermal stability-enhancing effect. Kinetic analysis showed that the activation energies (Ea) during degradation of composites were always higher than pure NR. However, Ea reached its maximum at 0.1 wt% GE content and started to decrease with further increase in GE loading. The changes in the thermal properties were attributed to the chemical structure and heat transfer properties of graphene sheets.

The influence of highly dispersed Cu2O-anchored MoS2 hybrids on reducing smoke toxicity and fire hazards for rigid polyurethane foam

The extensive utilization of rigid polyurethane foam (RPUF) as construction insulation material has brought two main troubles to our society: fire risks and toxic hazards. To reduce the fire hazards of RPUF, a layered MoS₂ decorated with Cu₂O nanoparticles was creativity obtained by hydrothermal technology and facile wet chemical treatment for reducing the toxic product formations of polyurethane nanocomposites during combustion. Due to the low weight ratio of Cu₂O attached onto MoS₂, the resulting Cu₂O-MoS₂ hybrid effectively prevented the MoS₂ nanosheets from restacking. However, the Cu₂O-MoS₂-M hybrid was produced by increasing content of Cu₂O, which has the characteristic stacked layer structure of MoS₂. Reduced harmful organic volatiles and the toxic gases (e.g. a respective decrease of ca. 28% and 53% for CO and NO_x products) were obtained because of synergistic effect between the physical adsorption of MoS₂ and catalysis action of Cu₂O. Notably, the addition of Cu₂O-MoS₂ hybrids led to high char formation of the RPUF nanocomposite, indicating the effectively catalytic carbonization property. In addition, the N-Gas model for predicting fire smoke toxicity was developed and demonstrated. Furthermore, the research offers direct proofs of the negative influence of the stacked MoS₂ on reducing the smoke toxicity for RPUF nanocomposites.

Facile synthesis of aluminum branched oligo(phenylphosphonate) submicro-particles with enhanced flame retardance and smoke toxicity suppression for epoxy resin composites

A novel and submicro-scale aluminum branched oligo(phenylphosphonate) (AHPP) has been successfully synthesized and embedded into a polymeric substrate to improve the fire safety of epoxy resin (EP). The chemical structures of intermediates and target products were characterized using the nuclear magnetic resonance spectroscopy, X-ray diffraction and Fourier transform infrared analysis. Morphology analysis confirmed that all of the as-synthesized AHPP submicro-particles are mutually well-separated. Combustion results demonstrated that the limiting oxygen index value is increased to 30.5% from 23.5% while the PHRR and THR are decreased by ca. 68.1% and 41.2%, respectively for the EP/AHPP-7.5 composite compared to the corresponding values for pure EP. In addition, the binary blends display the satisfying smoke toxicity suppression performance during combustion. The total smoke production and the total CO yield for EP/AHPP-7.5 are dramatically reduced by 62.0% and 32.3%, respectively, which may mainly be ascribed to the catalytic carbonization performance of the polymers and formation of Al₂O₃ layers on the surface of the char residues. As a result, the findings in this study enabled the submicro-scale phosphorus-containing flame retardant to be a potential candidate as an efficient additive for reducing smoke toxicity of polymer composites.

3D printed nanocomposites using polymer grafted graphene oxide prepared by multicomponent Passerini reaction

The surface of commercial graphene oxide was modified with polymers using Passerini reaction, which enhances the compatibility between nanoparticles and 3D printing resin.

Friction and mechanical properties of amino-treated graphene-filled epoxy composites: modification conditions and filler content

It remains a challenge for graphene to reach its full potential as a lubricant and wear-resistant material in thermosetting resin composites. In this study, the mechanical properties and friction properties of amino-treated graphene-filled epoxy composites, which were influenced by the conditions for the modification of graphene and filler content, were investigated. The mechanical properties were measured by tensile examination and the tribological properties were determined using a ball-on-disk tribometer. The results showed that the composite filled with amino-treated graphene for a short reaction time exhibited the best tribological behavior, where the friction coefficient was 57.9% lower than that of the pure resin and the wear rate was 92.2% less than that of the neat resin. Simultaneously, this amino-treated graphene also resulted in enhanced mechanical properties and T_g in the nanocomposite, implying its good crosslinking network and strong interface strength. The wear track analysis demonstrated that the excellent wear resistance was induced by its improved toughness, which restrained the crack propagation of fatigue wear and decreased the size of debris, promoting the formation of a transfer film, and thus protecting the contact surface. The tribological properties also varied with the concentration of the nanofiller, which showed the best performance at 0.2 wt%. Through the optimization of the modification conditions and concentration, this work highlights a promising strategy for the application of graphene-related materials in the field of tribology.

The enhancement in resistance to the propagation of cracks in epoxy composites by adding GO-0.5 results in excellent wear resistance.

Polymer grafting on graphene layers by controlled radical polymerization

In situ controlled radical polymerization (CRP) is considered as an important approach to graft polymer brushes with controlled grafting density, functionality, and thickness on graphene layers. Polymers are tethered with chain end or through its backbone to the surface or edge of graphene layers with two in situ polymerization methods of "grafting from" and "grafting through" and also a method based on coupling reactions known as "grafting to". The "grafting from" method relies on the propagation of polymer chains from the surface- or edge-attached initiators. The "grafting through" method is based on incorporation of double bond-modified graphene layers into polymer chains through the propagation reaction. The "grafting to" technique involves attachment of pre-fabricated polymer chains to the graphene substrate. Here, physical and chemical attachment approaches are also considered in polymer-modification of graphene layers. Combination of CRP mechanisms of reversible activation, degenerative (exchange) chain transfer, atom transfer, and reversible chain transfer with various kinds of grafting reactions makes it possible to selectively functionalize graphene layers. The main aim of this review is assessment of the recent advances in the field of preparation of polymer-grafted graphene substrates with well-defined polymers of controlled molecular weight, thickness, and polydispersity index. Study of the opportunities and challenges for the future works in controlling of grafting density, site-selectivity in grafting, and various topologies of the brushes with potential applications in stimuli-responsive surfaces, polymer composites, Pickering emulsions, coating technologies, and sensors is also considered.

Immobilization of rubber additive on graphene for high-performance rubber composites

It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.

Effects of poly(ethylene glycol)-grafted graphene on the electrical properties of poly(lactic acid) nanocomposites

Maleic anhydride was reacted with the armchair edges of graphene nanosheets (GN) via Diels-Alder reaction. Then, polyethylene glycol (PEG) was grafted onto the GN in the presence of anhydride groups through an esterification reaction. The PEG-grafted GN (PEG-g-GN) was characterised via FTIR analysis, thermogravimetric analysis, scanning electron microscopy, Raman spectroscopy and contact angle measurements, proving that PEG was successfully grafted onto the GN surface. The results indicated that PEG-g-GN possessed high electrical conductivity and was dispersed in polylactic acid (PLA). The composites were fabricated by using PEG-g-GN and GN as the conductive agent in the PLA matrix. Owing to the function of PEG molecular chains, PEG-g-GN can be uniformly dispersed in the PLA matrix and improve the tensile strength of composites to 59.46 MPa and conductivity to 9.69 × 10-4 S cm-1 at a PEG-g-GN content of 1 wt%.

Constructing Long-Range Transfer Pathways with Ordered Acid-Base Pairs for Highly Enhanced Proton Conduction

Acid-base pairs hold great superiority in creating proton defects and facilitating proton transfer with less or no water. However, the existing acid-base complexes fail in assembling into ordered acid-base pairs and thus cannot always take full advantage of the acid-base synergetic effect. Herein, polymer quantum dots with inherent ordered acid-base pairs are utilized and anchored on dopamine-coated graphene oxide, thus forming into long-range conducting pathways. The resultant building blocks ( _nPGO) are integrated in a sulfonated poly(ether ether ketone) matrix to fabricate composite membranes. The constructed long-range transfer highways with ordered acid-base pairs impart to the composite membrane significantly enhanced proton conduction ability. Under the hydrated state, the composite membrane attains 91% increase over the control membrane in conductivity, and the single-cell fuel based on the membrane achieves 71% promotion in maximum power density. Under anhydrous conditions, more striking augment in conduction is observed for the composite membrane, reaching 7.14 mS cm^-1, almost 10 times of the control membrane value (0.78 mS cm^-1). Remarkably, such anhydrous proton conduction performance is even comparable to that of the composite membrane impregnated with ionic liquids, which is hard to realize with conventional fillers. Collectively, these results endow composite membranes great potential for applications in hydrogen-based fuel cells, sensors, and catalysis.

Achieving high-performance epoxy nanocomposites with trifunctional poly(oxypropylene)amines functionalized graphene oxide

In this article, two types of functional graphene oxide (GO) with amine-rich surface were synthesized through chemically grafting two different molecular chain length trifunctional poly(oxypropylene)amines T5000 and T403, which were named as T5000-GO and T403-GO, respectively. The functionalized GO was then added to epoxy (EP) resin. Fourier transform infrared spectra analysis confirmed successful chemical functionalization on GO. Both T403-GO and T5000-GO were tightly embedded in the EP, because the amine-rich surface of functionalized-GO could form covalent bonds with the EP matrix, thereby contributing to the enhancement of mechanical properties. Particularly, T5000-GO, which has longer grafting molecule chains, achieved better compatibility and dispersibility in the EP matrix, resulting in a better reinforcing efficiency in mechanical properties. For example, the T5000-GO/EP composites showed an incremental enhancement in tensile strength with increasing filler concentrations, whereas their T403-GO/EP counterparts failed to follow the same trend. Meanwhile, the T5000-GO/EP composites with only 0.1-wt% T5000-GO achieved a prominent increase in flexural strength (approximately 50%) and flexural modulus (approximately 26.8%), which were higher than those of T403-GO-filled counterparts. This work indicated that the compatibility and interphase between GO and EP could be designed by manipulating the length of grafting molecule chains, thereby providing a better understanding of the relationship between the structure and mechanical properties of the graphene/EP nanocomposites.

Graphene Oxide/Ferrocene-Containing Polymer/Gold Nanoparticle Triple Nanocomposite

A facile strategy to prepare GO-based nanocomposites with both gold nanoparticles (AuNPs) and ferrocene (Fc) moieties was developed. The surface of GO was modified with PFcMAss homopolymer by surface-initiated atom transfer radical polymerization of a new methacrylate monomer of 2-((2-(methacryloyloxy)ethyl)disulfanyl)ethyl ferrocene-carboxylate (FcMAss), consisting of disulfide as an anchoring group for stabilizing AuNPs and Fc group as an additional functionality. AuNPs with an average diameter of about 4.1 nm were formed in situ on the surface of PFcMAss-decorated GO (GO-PFcMAss) via Brust-Schiffrin method to give GO-PFcMAss-AuNPs multifunctional nanocomposites bearing GO, AuNPs and Fc groups. The obtained nanocomposites were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Since disulfide-containing polymers, rather than the commonly used thiol-containing compounds, were employed as ligands to stabilize AuNPs, much more stabilizing groups were attached onto the surface of GO, and thus more AuNPs were able to be introduced onto the surface of GO. Besides, polymeric chains on the surface of GO endowed GO-PFcMAss-AuNPs nanocomposites with excellent colloidal stability, and the usage of a disulfide group provides possibility to efficiently incorporate additional functionalities by easily modifying structure of disulfide-based monomer.

Fabrication of poly (trimethylene carbonate)/reduced graphene oxide-graft-poly (trimethylene carbonate) composite scaffolds for nerve regeneration

One of the key challenges for neural tissue engineering is to exploit functional materials to guide and support nerve regeneration. Currently, reduced graphene oxide (rGO), which is well-known for its unique electrical and mechanical properties, has been incorporated into biocompatible polymers to manufacture functional scaffolds for nerve tissue engineering. However, rGO has poor dispersity in polymer matrix, which limits its further application. Here, we replaced rGO with rGO-graft-PTMC. The rGO-graft-PTMC was firstly prepared by grafting trimethylene carbonate (TMC) oligomers onto rGO. Subsequently, PTMC/rGO-graft-PTMC composite fibrous mats were fabricated by electrospinning of a dispersion of PTMC and rGO-graft-PTMC. The loading of rGO-graft-PTMC could reach up to 6 wt% relative to PTMC. Scanning electron microscopy images showed that the morphologies and average diameters of PTMC/rGO-graft-PTMC composite fibrous mats were affected by the content of rGO-graft-PTMC. Additionally, the incorporation of rGO-graft-PTMC resulted in enhanced thermal stability and hydrophobicity of PTMC fibers. Biological results demonstrated that PC12 cells showed higher cell viability on PTMC/rGO-graft-PTMC fibers of 2.4, 4.0 and 6.0 wt% rGO-graft-PTMC compared to pure PTMC fibers. These results suggest that PTMC/rGO-graft-PTMC composite fibrous structures hold great potential for neural tissue engineering.

Hierarchically hydrogen-bonded graphene/polymer interfaces with drastically enhanced interfacial thermal conductance

Interfacial thermal transport is a critical physical process determining the performance of many material systems with small-scale features. Recently, self-assembled monolayers and polymer brushes have been widely used to engineer material interfaces presenting unprecedented properties. Here, we demonstrate that poly(vinyl alcohol) (PVA) monolayers with hierarchically arranged hydrogen bonds drastically enhance interfacial thermal conductance by a factor of 6.22 across the interface between graphene and poly(methyl methacrylate) (PMMA). The enhancement is tunable by varying the number of grafted chains and the density of hydrogen bonds in the unique hierarchical hydrogen bond network. The extraordinary enhancement results from a synergy of hydrogen bonds and other structural and thermal factors including molecular morphology, chain orientation, interfacial vibrational coupling and heat exchange. Two types of hydrogen bonds, i.e. PVA-PMMA hydrogen bonds and PVA-PVA hydrogen bonds, are analyzed and their effects on various structural and thermal properties are systematically investigated. These results are expected to provide new physical insights for interface engineering to achieve tunable thermal management and energy efficiency in a wide variety of systems involving polymers and biomaterials.

Thermo-Responsive Graphene Oxide/Poly(Ethyl Ethylene Phosphate) Nanocomposite via Ring Opening Polymerization

An efficient strategy for growing thermo-sensitive polymers from the surface of exfoliated graphene oxide (GO) is reported in this article. GO sheets with hydroxyls and epoxy groups on the surface were first prepared by modified Hummer's method. Epoxy groups on GO sheets can be easily modified through ring-opening reactions, involving nucleophilic attack by tris(hydroxymethyl) aminomethane (TRIS). The resulting GO-TRIS sheets became a more versatile precursor for next ring opening polymerization (ROP) of ethyl ethylene phosphate (EEP), leading to GO-TRIS/poly(ethyl ethylene phosphate) (GO-TRIS-PEEP) nanocomposite. The nanocomposite was characterized by ¹H NMR, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential thermal gravity (DTG), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Since hydrophilic PEEP chains make the composite separate into single layers through hydrogen bonding interaction, the dispersity of the functionalized GO sheets in water is significantly improved. Meanwhile, the aqueous dispersion of GO-TRIS-PEEP nanocomposite shows reversible temperature switching self-assembly and disassembly behavior. Such a smart graphene oxide-based hybrid material is promising for applications in the biomedical field.

Polyarylene Ether Nitrile-Based High-k Composites for Dielectric Applications

Flexible polymer-based composites exhibiting high dielectric constant as well as low dielectric loss have been intensively investigated for their potential utilization in electronics and electricity industry and energy storage. Resulting from the polar -CN on the side chain, polyarylene ether nitrile (PEN) shows relatively high dielectric constant which has been extensively investigated as one of the hot spots as dielectric materials. However, the dielectric constant of PEN is still much lower than the ceramic dielectrics such as BaTiO3, TiO2, and Al2O3. In this review, recent and in-progress advancements in the designing and preparing strategies to obtain high-k PEN-based nanocomposites are summarized. According to the types of the added fillers, the effects of organic fillers, dielectric ceramic fillers, and conductive fillers on electric properties of PEN-based composites are investigated. In addition, other factors including the structures and sizes of the additive, the compatibility between the additive agent and the PEN, and the interface which affects the dielectric properties of the obtained composite materials are investigated. Finally, challenges facing in the design of more effective strategies for the high-k PEN-based dielectric materials are discussed.

Mussel-inspired functionalization of electrochemically exfoliated graphene: Based on self-polymerization of dopamine and its suppression effect on the fire hazards and smoke toxicity of thermoplastic polyurethane

The suppression effect of graphene in the fire hazards and smoke toxicity of polymer composites has been seriously limited by both mass production and weak interfacial interaction. Though the electrochemical preparation provides an available approach for mass production, exfoliated graphene could not strongly bond with polar polymer chains. Herein, mussel-inspired functionalization of electrochemically exfoliated graphene was successfully processed and added into polar thermoplastic polyurethane matrix (TPU). As confirmed by SEM patterns of fracture surface, functionalized graphene possessing abundant hydroxyl could constitute a forceful chains interaction with TPU. By the incorporation of 2.0 wt % f-GNS, peak heat release rate (pHRR), total heat release (THR), specific extinction area (SEA), as well as smoke produce rate (SPR) of TPU composites were approximately decreased by 59.4%, 27.1%, 31.9%, and 26.7%, respectively. A probable mechanism of fire retardant was hypothesized: well-dispersed f-GNS constituted tortuous path and hindered the exchange process of degradation product with barrier function. Large quantities of degradation product gathered round f-GNS and reacted with flame retardant to produce the cross-linked and high-degree graphited residual char. The simple functionalization for electrochemically exfoliated graphene impels the application of graphene in the fields of flame retardant composites.