Super Strong and Tough Polybenzimidazole/Metal Ions Coordination Networks: Reinforcing Mechanism, Recyclability, and Anti-Counterfeiting Applications.

Nature has provided many delicate strategies for optimizing the structural characteristics of biological materials. One such strategy is the strengthening and toughening of matrix materials by aduandant and hierarchically arranged non-covalent crosslinking. However, efficient strengthening and toughening of high-performance aromatic polymers by non-covalent bonds has rarely been reported yet. Herein, we report the preparation and characterizations of a metal coordination bonds crosslinked polybenzimidazole (PBI) network. By optimizing the synthetic parameters, the strength of copper ion (Cu2+ ) crosslinked PBI is improved from 87.8 to 218.4 MPa, and the toughness is increased from 19.4 to 111.9 MJ m-3 , corresponding to increments of 148.7 % and 476.8 %, respectively, which surpass all previously reported non-covalent bonds crosslinked high-performance polymers. PBI with varied chain flexibility are then synthesized to deeply understand the stregnening and toughening mechanism. In addition, the glass transition temperature of PBI is dramatically increased by 75 °C after Cu2+ crosslinking. Moreover, the chemical recycling of PBI from crosslinekd network, and the development of a novel high-temperature resistant or high-temperature rewritable anti-counterfeiting films based on Cu2+ crosslinked PBI are also demonstrated. This study is expected to shed light on design principle for future supramolecularly crosslinked and recyclable high-performance polymers.

Lysosome-targetable selenium-doped carbon nanodots for in situ scavenging free radicals in living cells and mice.

Lysosome-targetable selenium-doped carbon nanodots (Lyso-Se-CDs) that can efficiently scavenge lysosomal •OH in living cells and mice were designed in this research. Se-CDs with redox-responsive fluorescence (λex = 379 nm, λem = 471 nm, quantum yield = 7.1%) were initially synthesized from selenocystine by a facile hydrothermal method, followed by the surface modification with morpholine, a lysosome targeting moiety. The as-synthesized Lyso-Se-CDs exhibited excellent colloidal stability, efficient scavenging abilities towards •OH, low biotoxicity, as well as good biocompatibility and lysosome targetability. Due to these desirable properties, Lyso-Se-CDs had been successfully utilized for rescuing cells from elevated lysosomal •OH levels. More importantly, Lyso-Se-CDs efficiently relieved phorbol 12-myristate 13-acetate (PMA) triggered ear inflammation in live mice. These findings reveal that Lyso-Se-CDs are potent candidates for treating •OH-related inflammation.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration.

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

An efficient and general method for the synthesis of stable isotope deuterium labeled phthalate esters.

An efficient and general synthetic route of deuterium-labeled phthalate esters is described with high isotopic enrichment and excellent chemical purities using inexpensive and readily available o-xylene-D10 as labeled starting material. The structures and isotope-abundance were confirmed via 1 H NMR and mass spectrometry. These deuterium labeled phthalate esters can be used as analytical reference standards for the detection of plasticizer residues in soil, water, food, plastic products, etc.

Hyper-Cross-Linked Polymers-Derived Porous Tubular Carbon Nanofibers@TiO2 toward a Wide-Band and Lightweight Microwave Absorbent at a Low Loading Content.

An enormous challenge exists in the achievement of one-dimensional (1D) dielectric carbon composite high-performance microwave absorbents at a low filling ratio. Porous/core-shell dual microstructures have been considered as the potential candidate for designing remarkable microwave absorbers with strong absorption and wide band. Herein, novel multiple-structured tubular carbon nanofibers@TiO2 (TCNFs@TiO2) hybrids were constructed via the sequential steps of hydrolysis and pyrolysis. The dielectric properties of the as-prepared composites can be tuned by adjusting the relative content of the TiO2 shell and carbonaceous temperature to enhance the impedance matching behavior. Notably, the minimum reflection loss (RLmin) value reaches up to -61.2 dB with an effective absorption bandwidth (EAB) of 3.2 GHz at 3 mm, and the EAB can cover 5.3 GHz with a thickness of merely 2 mm when 1.3 mL of tetrabutyl titanate (TBT) and 700 °C pyrolysis temperature are optimized, respectively. Delightedly, the mixing ratio is only 10 wt %, outperforming that of the most-related composites. The heterogeneous interfaces in TCNFs-TiO2 are beneficial for the interfacial polarization relaxation. Besides, the hybrids are enriched with numerous pores to favor the lightweight absorbers. The desirable design in the microstructure can provide a promising route in wide-band and lightweight microwave absorbents.

Mechanical strong stretchable conductive multi-stimuli-responsive nanocomposite double network hydrogel as biosensor and actuator.

Multi-stimuli- responsive mechanical strong stretchable hydrogel has grabbed extensive attention in recent years. Here, a novel stretchable conductive biocompatible near-infrared light(NIR)-/thermal-/pH-/ionic concentration- responsive carboxymethyl chitosan (CMCTs)/graphene oxide (GO)/poly(N-isopropylacrylamide)(PNIPAm) nanocomposite double network hydrogel was fabricated through a simple one-pot in situ free radical polymerization, which is initiated by ultraviolet (UV) light and using N-(3-dimethylaminopropyl)-N-ethylcarbodiimidehydrochloride (EDC) and N,N'-bis(acryloyl)cystamine (BAC) as cross-linkers respectively, instead of toxic organic molecules. When the concentration of CMCTs, GO, EDC and BAC is 22.50, 0.103, 7.50 and 0.467 mg/mL respectively, the obtained hydrogel sample owns the highest tensile strength of 1046 kPa at failure strain of 1286% and a corresponding compressive stress of 2.37 MPa at deformation of 90%. Besides, these hydrogels have an obvious pH-/thermal-/ionic concentration-responsive properties depending on the concentration of the above mentioned factors, and their good conductive property makes them as candidate material for healthcare biosensors. Finally, we attempt to design a novel thermal-/NIR-responsive double network structure bilayer hydrogel, which has the potential use as remote actuator in dangerous places in the future.

Vitrimer Chemistry Assisted Fabrication of Aligned, Healable, and Recyclable Graphene/Epoxy Composites.

The alignment is a key factor to fully exploit the potential of graphene in reinforcement of polymer composites. However, it is still a challenge to orientate graphene in thermosets because of the insoluble and infusible features of the later. In this paper, we report a facile and scalable hot press method to fabricate aligned graphene nanoplate (GnP)/epoxy composites by utilizing the dynamic character of epoxy vitrimer. The bond exchange and topological rearrangement associated viscous flow of epoxy vitrimer during hot press allows the spontaneous orientation of GnP in matrix because the 2D structure and volume exclusion effect. SEM images demonstrate the orientation of GnP, while tensile test reveals the significantly increased reinforcement effect of GnP on matrix after hot press. Moreover, the dynamic reaction of epoxy vitrimer confers good healability and recyclability to the aligned composites as confirmed by the nearly fully recovered mechanical properties of the healed sample after cutting, and the recycled sample after grinding. This work is expected to provide new opportunity for fabrication of aligned thermosetting composites.

High Performance Microfiltration Composite Membranes Based on Phenolphthalein Poly(ether sulfone) Nanofibrous Substrate with Hydrophilic Coating.

In the present paper, Phenolphthalein poly(ether sulfone) (PES-C) nanofibrous membranes were prepared via solution-blowing technology and polyvinylpyrrolidone (PVP) which would be converted to stable gels by reaction with potassium persulfate (K2S2O8) was immobilized on the surface of nanofibers. The influence factors such as PVP concentration and depositing time were optimized to obtain the composite nanofibrous membranes. The membranes were characterized by Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Wide-angle X-ray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS) and Water contact angles (WCA), etc. The hydrophilicity of the composite membrane was significantly enhanced by immobilizing Polyvinylpolypyrrolidone (PVPP) on the surface of nanofibers. Furthermore the filtration experiment of starch suspension and oil-water separation test were executed and the anti-fouling properties of the modified membranes were evaluated with the flux recovery ratio (FRR%). The results showed that membranes with PVPP-modified had a more excellent and stability antifouling performances compared with the original membranes. Generally, this work provides a simple and useful method to improve anti-fouling properties of PES-C nanofibrous membranes which had great potential application in microfiltration.

Tough robust dual responsive nanocomposite hydrogel as controlled drug delivery carrier of asprin.

Smart mechanical strong hydrogels have gained increasing attention in the last decade. A novel tough robust biocompatible and dual pH- and temperature- responsive poly (N-isopropylacrylamide)/clay (Laponite XLS)/gold nanoparticles (Au-S-S NPs)/caboxymethyl chitosan (CMCTs) nanocomposite hydrogel was synthesized by a facile one-pot in situ free radical polymerization, using clay and Au-S-S NPs as the cross-linkers instead of toxic organic molecules. By tuning the crucial factors, concentration of Au-S-S NPs, CMCTs and clay, the obtained hydrogels exhibited the highest tensile stress of 535.5 kPa at the breaking deformation of 1579.5%. Furthermore, these synthesized hydrogels were tough enough and simultaneously owned a fast recoverability after unloaded in 15 min at room temperature. Moreover, effects of the above factors on swelling and swelling-shrinking behaviors of the prepared hydrogels were investigated in detail. In addition, these designed hydrogels also possessed a controlled drug release property of asprin by adjusting their inner crosslink density. Owing to this property, they could be used as the potential drug delivery carriers in future.

Mechanically strong dual responsive nanocomposite double network hydrogel for controlled drug release of asprin.

Mechanically strong dual/multi-stimuli-responsive smart hydrogels have attracted extensive attention in recent years. A novel tough, mechanical strong and biocompatible dual pH- and temperature- responsive poly (N-isopropylacrylamide) /clay (laponite XLG)/carboxymethyl chitosan (CMCTs) /genipin nanocomposite double network hydrogel was synthesized through a facile, one-pot free radical polymerization initiated by the ultraviolet light, using clay and the natural molecular-genipin as the cross-linkers instead of toxic organic molecules. Crucial factors, the content of CMCTs, clay and genipin, for synthesizing the mechanical strong hydrogels were investigated. When the content of CMCTs, clay and genipin were 5 wt%, 33.3 wt% and 0.175 wt%, respectively (to the weight of N-isopropylacrylamide), these prepared hydrogels exhibited a high tensile strength of 137.9 kPa at the failure strain of 446.1%. Furthermore, the relationship between swelling and deswelling rate of the synthesized hydrogels and the above crucial factors were also studied. Besides, the synthesized hydrogels displayed a considerable controlled release property of asprin by tuning their inner crosslink density. Owing to this property, they may have great potential in the drug delivery systems.

Preparation of Solution Blown Polyamic Acid Nanofibers and Their Imidization into Polyimide Nanofiber Mats.

Solution blow spinning (SBS) is an innovative process for spinning micro/nanofibers. In this paper, polyamic acid (PAA) nanofibers were fabricated via a SBS apparatus and then imidized into polyimide (PI) nanofibers via thermal process. The morphology and diameter distributions of PAA nanofibers were determined by scanning electron microscope (SEM) and Image Tool software, the processing parameters, including PAA concentration, solution feeding rate, gas pressure, nozzle size, and receiving distance were investigated in details. The fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical changes in the nanofibers after thermal imidization. The results showed that the solution concentration exhibited a notable correlation with spinnability, and the formation of bead defects in PAA nanofibers. Solution feeding rate, gas pressure, nozzle size, and receiving distance affected nanofiber production efficiency and diameter distribution. The average diameters of fibers produced ranged from 129.6 to 197.7 nm by varying SBS parameters. Precisely, PAA nanofibers with good morphology were obtained and the average diameter of nanofibers was 178.2 nm with optimum process parameter. After thermal imidization, the PI nanofibers exhibited obvious adhesion morphology among interconnected fibers, with an increased average diameter of 209.1 nm. The tensile strength of resultant PI nanofiber mat was 12.95 MPa.

Mechanically strong and pH-responsive carboxymethyl chitosan/graphene oxide/polyacrylamide nanocomposite hydrogels with fast recoverability.

The biocompatible, quickly recoverable, mechanically strong and tough polymer hydrogels have great potential for biomedical applications. A novel carboxymethyl chitosan (CMCTs)/graphene oxide (GO)/polyacrylamide (PAM) nanocomposite (NC) hydrogel with excellent mechanical performance was synthesized through a facile, one-pot free radical polymerization, using GO nanosheets as the crosslink centers instead of toxic organic molecules. The content of GO nanosheets and CMCTs has great influence on the mechanical properties of CMCTs/GO/PAM NC hydrogels. When the amount of GO nanosheets is 0.118 wt % and CMCTs is 1.5 wt % (to the total weight of CMCTs and acrylamide), CMCTs/GO/PAM hydrogel displays a compressive stress as high as 5.8 MPa at the breaking deformation of 87.5% and a tensile strength of 223.6 kPa at the failure strain of 631%. Besides, with nearly complete recovery in 1 min at the room temperature after unloading, the CMCTs/GO/PAM hydrogels exhibit excellent fast recoverability. Additionally, the CMCTs/GO/PAM hydrogels also have an obvious pH-responsive property.

Mussel-adhesive-inspired fabrication of multifunctional silver nanoparticle assemblies.

The assembly of metal nanoparticles (NPs) has attracted a great deal of attention recently because of their collective properties that could not be exhibited by individual NPs. Here a one-step approach was reported for the fabrication of spherical silver NP assemblies (AgNAs). The formation of AgNAs simply included the stirring of silver ammonia and 3,4-dihydroxy-l-phenylalanine (DOPA) in aqueous solution at room temperature, in which DOPA acted as a reductant for AgNPs first because of its reducing ability and then directed the assembly of AgNPs into AgNAs. The AgNAs exhibited hierarchical structure with controllable sizes ranging from 180 to 610 nm by adjusting the concentrations of reagents. The two individual components, AgNPs and polyDOPA, also allowed AgNAs with multiple functions as demonstrated in this study of durable catalytic activity, high SERS sensitivity, and good antioxidant properties. The thin polyDOPA layer coated on AgNAs further offered the opportunity to modify the surface of AgNAs. The results presented here may provide a green and facile approach to designing multifunctional NP assemblies.

Tuning bio-inspired skin-core structure of nascent fiber via interplay of polymer phase transitions.

The properties of polymer fibers are determined by their inner structures. We performed dynamic Monte Carlo simulations of early-stage solidification in the fluid filaments of stretched polymer solutions after extrusion into a coagulation bath upon fiber spinning. We observed that the radial temperature gradient dominates polymer crystallization to form an oriented crystalline skin (from single to multiple layers), while the radial non-solvent influx dominates phase separation to form a concentrated but less oriented core. The skin-core structure offers fibers a balanced performance between strength and toughness similar to plant stems, which can be tuned by the interplay of phase transitions. Our molecular-level observations facilitate a systematic understanding of the microscopic mechanism of fiber-spinning, which will pave a way towards making excellent polymer fibers.

Helical organic nanotubes from simple chiral building blocks.

Utilizing simple organic chiral (S)-(-)- and (R)-(+)- 1,1'-binaphthyl-2,2'-diamino as building blocks, one-dimensional chiral nanofibers/tubes were assembled via a simple process. Morphology and structure of the building blocks and the assemblies were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while formation and properties of the assemblies were studied by ultraviolet-visible (UV-Vis) spectrophotometer, Fourier transform infrared (FTIR) spectrometer, X-ray diffractometer (XRD) and Circular dichroism (CD) spectropolarimeter. Results show that left-handed and right-handed nanofibers were successfully assembled via this method, and the structure and morphology of the assembled nanofibers are heavily dependent on assembling conditions and intrinsic molecular information of the building blocks. Additionally, water contact angle measurements were conducted to investigate surface wetting properties of the nanotubes, indicating a superhydrophobic surface and the possibility of achieving novel and additional properties by assembling building blocks into an ordered supermolecular structure. This work provides a simple method to prepare helical organic nanomaterials of interest for various applications.

Construction of robust enzyme nanocapsules for effective organophosphate decontamination, detoxification, and protection.

Nanocapsules of organophosphorous hydrolase with enhanced enzyme activity and stability are prepared via in situ polymerization, providing a novel class of nanoparticles for the decontamination and detoxification of organophosphates such as chemical warfare agents and pesticides. Using the nanocapsules as building blocks, bioactive nanocomposites are also fabricated, enabling their use for organophosphate protection.

Tuning hierarchically aligned structures for high-strength PMIA-MWCNT hybrid nanofibers.

Novel hierarchically aligned PMIA-MWCNT hybrid nanofibers with a robust tensile strength of 316.7 MPa were prepared by a facile electrospinning process. The critical roles of humidity and MWCNT contents in tuning hierarchically aligned structures were first proposed, and a two-step break mechanism upon external stress was confirmed.

Study on morphology and characterization of poly(mphenylene isophtalamide)/multi-walled carbon nanotubes composite nanofibers by electrospinning.

Electrospinning technique is the main method of preparing polymer nanofiber simply, directly and continuously at present. In this work, electrospinning blend solution was prepared by in-situ polymerization using acid-modified multi-walled carbon nanotubes (MWNTs), m-phenylenediamine (MPD) and isophthaloyl chloride (IPC). And then composite nanofibers were prepared by electrospinning. MWNTs played an important role in nanofiber's properties. The effects of MWNTs on the morphology and characterization of the MWNTs/PMIA composite nanofibers were investigated. Scanning electron microscopy (SEM), thermal gravimetric analyzer (TGA), and X-ray diffraction (XRD) were utilized to characterize the MWNTs/PMIA nanofibers morphology and properties. The experimental results indicated that the nanofibers diameter decreased and solution dynamic viscosity increased with increasing MWNTs contents. XRD data demonstrated that PMIA composite nanofibers had the same crystal type as the pure PMIA nanofiber, and crystallinity was improved with increasing MWNTs loading. Transmission electron microscopy (TEM) was used to confirm MWNTs aligned along the axis of composite nanofibers.

Effects of three parameters on the diameter of electrospun poly(ethylene oxide) nanofibers.

The combined use of two techniques namely electrospray and spinning is made use in a highly versatile technique called electrospinning, which produces the diameter of polymer fibers range from nanometer to sub-micron. In this work, we have studied effects of adding LiCl on the morphology and diameter of electrospun poly(ethylene oxide), and we have also evaluated systematically the effect of three important solution parameters on the morphology of electrospun poly(ethylene oxide): molecular weight, solution viscosity and electrical conductivity. We find that molecular weight is strongly correlated with the formation of bead defects in the fibers, the smaller molecular weight, the more beads defect density. As a result, the fibers have beads-in-string structures. Electrical conductivity increases, then decreases as molecular weight increases. Solution viscosity has been found to most strongly affect fiber size, with fibers diameter increasing with increasing solution viscosity according to a power law relationship. In addition, we find evidence that solution viscosity and electrical conductivity affect the interesting morphology of the electrospun nanofibers, and result in doubling and forming membrances phenomena.

Dynamic rheological studies of poly(p-phenyleneterephthalamide) and carbon nanotube blends in sulfuric acid.

We have studied the dynamic scanning of liquid-crystalline (LC) poly(p-phenyleneterephthalamide) sulfuric acid (PPTA-H(2)SO(4)) solution, and its blend with single-walled carbon nanotubes (SWNTs), by using a flat plate rotational rheometer. The effects of weight concentration and molecular weight of PPTA, as well as operating temperature, on dynamic viscoelasticity of the PPTA-H(2)SO(4) LC solution system are discussed. The transition from a biphasic system to a single-phase LC occurs in the weight concentration range of SWNTs from 0.1% to 0.2%, in which complex viscosity reaches the maximum at 0.2 wt% and the minimum at 0.1 wt%, respectively, of SWNTs. With increasing SWNT weight concentration, the endothermic peak temperature increases from 73.6 to 79.9 degrees C. The PPTA/SWNT/H(2)SO(4) solution is in its plateau zone and storage modulus (G') is a dominant factor within the frequency (omega) range of 0.1-10 rad/s. As omega increases, the G' rises slightly, in direct proportion to the omega. The loss modulus (G'') does not rise as a function of omega when omega < 1 s(-1), then when omega > 1 s(-1) G'' increases faster than G', yet not in any proportion to the omega.