Search

When joint inventory positions in an assemble-to-order system are irreducible, it has been proved that the evaluation on order-based backorders can be based on a set of systems under the base stock policy. We provide a new necessary and sufficient condition for the irreducibility of the joint inventory positions where the item inventory is controlled by an ( r , n Q ) policy. The computation complexity of applying this new condition is much lower than that of verifying the previous condition.

In this study, we design a novel thermo- and photo-responsive nanocomposite film prepared by depositing indium tin oxide nanocrystals via the coating of amphiphilic copolymer on polycaprolactone substrates (INCP). The INCP film shows reversible surface morphology change properties by changing temperature as well as turning ON/OFF NIR laser. Especially, as the temperature changes from 25 to 75 °C, the film could regulate light transmittance from 75 to 90% across the visible and near-infrared region (500–1,750 nm). In addition, the film also exhibits excellent recycle and thermal stability at different temperature. Our results reveal that reversible surface morphology change properties are caused by curvature adjustment of film, which is owing to the coupling effect between copolymer and PCL with different thermal expansion strains. Our results suggest a possible strategy for the preparation of smart responsive materials in the future, which provides a reference for the development of new energy-saving materials.

Fiber metal laminate (FML) is a sandwich combination of thin metal and a composite layer which possess high fatigue, creep, and corrosion resistance. The performance of FML depends on the bonding behavior between the metal and composite interface (MCI). Introducing Redux 335k polymer interleaf can improve MCI, but cannot retain the mechanical properties after its first delamination. Toughened self-healing co-polymer film EMAA (Ethylene-methacrylic acid) can be used as an alternative due to its self-healing property which can recover the mechanical property after each delamination. Double-cantilever-beam (DCB) test is carried out by supporting a thick CFRP composite as a backing beam to avoid the yielding of thin metal in FML to estimate the interlaminar fracture toughness (G1C) at the MCI. Results from the DCB test shows that the incorporation of EMAA thin film improves G1C at the MCI. However, G1C gradually decreases despite recovering its fracture toughness after each delamination when the self-healing reaction is thermally activated. The Mode I fracture toughness of EMAA before the first heal is 1.95 kJ/m2, which is higher due to its thermoplastic nature. This article emphasizes only on the recovery of Mode I self-healing efficiency of EMAA at MCI. However, the article also shows the fracture toughness at MCI by using non-self-healing film adhesive at MCI. This comparison is to understand that the standard structural adhesive (Redux 335K) cannot retain the mechanical properties after its first delamination, and also to understand the failure modes of both thermosetting and thermoplastic interleaf at MCI.

The understanding of the shell formation mechanism for the novel encapsulation technique via integrating microfluidic T-junction and interfacial polymerization is not only important to fabricate hi...

The fiber phase, matrix phase, and fiber/matrix interphase are different phases of fiber reinforced polymers (FRPs). FRP property such as mechanical strength is highly dependent on the adhesion level between the fiber and matrix for efficient load transfer. In this study, functionalized multiwalled carbon nanotubes (MWCNT) modified dopamine coating solution is coated on the fiber surface as additional sizing to enhance the interfacial bonding strength between ultra-high-molecular-weight polyethylene (UHMWPE) fiber and thermoplastic matrix (Elium®) which has resin infusion capability. The resultant of transverse fiber bundle tests shows that the polydopamine (PDA) coating of fiber with embedded 0.03% of MWCNT can improve the bonding strength of fiber/matrix about 42.50% compared with that of common composites. In contrast, the addition of carbon nanotubes into Elium® matrix shows a distinctly weaker bonding effect than the interphase between neat PDA coating and UHMWPE fiber. This discrepancy is because of densification of carbon nanotubes (CNT) forest grafted on the fiber surface during the nanocomposite coating process. When being compared to other surface modification process, CNT embedded dopamine surface modification is cost effective and less time consuming and has better performance than the modified matrix with the addition of CNTs.

Polymers are susceptible to small damage which is difficult to detect and repair and may lead to catastrophic failure if left unattended at the early stage. How to autonomously warn and repair the damage simultaneously is a promising yet challenging task, owing to the difficulty in integrating different functional elements for packaging and lack of suitable vehicles to carry a multirole trigger with high reactivity. Herein, inspired by human skin in the damage-healing process, we report a genuinely fully autonomous smart material that is capable of warning of and healing damage via simply incorporating dual microcapsules containing polyamine as a multirole trigger and epoxy monomer dyed with a pH indicator, respectively. Both microscopic "subcutaneous" damage and macroscopic surface damage can be warned of by a conspicuous red color, not only rapidly upon occurrence but also permanently after being repaired. Accompanied with the comprehensive warning, the smart material shows high healing performance upon dynamic impact damage with efficiency up to 100% without external interventions. This facile and ready strategy with fully autonomous warning and healing functions independent of the host matrix provides a new avenue to enhance the reliability and longevity of a wide variety of polymeric materials ranging from functional coatings to structural composites. We thank the SUG from HKUST (R9365) and Hong Kong Research Grants Council (Project No. N_HKUST631/18), the Key Program of National Natural Science Foundation of China (Grant No. 51435005), the National Instrumentation Program (Grant No. 2012YQ230043), the Science and Technology Program of Guangzhou (Grant No. 201607010240), and the Science and Technology Planning Project of Guangdong Province (Grant No. 2015B090904004 and 2018A030313264), for financial support.

In this work, shear thickening fluid (STF) was fabricated and encapsulated by using three different encapsulation methods for the first time. The mechanical properties of individual STF capsules were investigated to obtain optimal encapsulation method and formula. Much more energy can be absorbed for STF capsules during impact than that of quasi-static compression. The introduction of ultraviolet (UV) curable resin can significantly improve the static strength of STF capsule and thus enhance the handleability of STF capsule. The STF capsules synthesized through the two-step polymerization method show an elastic shell which can stand multiple impacts without any damage. This STF capsule possesses higher static strength and absorbs more strain energy than capsules synthesized through the other two methods. Furthermore, incorporation of the STF capsules into silicone gel enhances the energy absorption capacity of matrix material up to 71.3%. Accepted version

Microencapsulated phase-change material (ME-PCM) employing octadecane as a core material has been practiced for thermal-energy-storage (TES) applications in buildings. However, octadecane as a hydrocarbon-based PCM is flammable. Herein, silica-shelled microcapsules (SiO2-MCs) and poly(urea-formaldehyde)-shelled microcapsules (PUF-MCs) were successfully prepared, loaded with octadecane/tributyl phosphate (TBP) as hybrid core materials, which not only exhibited good TES properties but also high-effective flame retardancy. SiO2-MC (ΔHm = 124.6 J g-1 and ΔHc = 124.1 J g-1) showed weaker TES capacity than PUF-MC (ΔHm = 186.8 J g-1, ΔHc = 188.5 J g-1) but better flame retardancy with a lower peak heat-release rate (HRRpeak) of 460.9 W g-1 (556.9 W g-1 for PUF-MCs). As compared with octadecane (38.7 kJ g-1), the reduction in total heat release (THR) for SiO2-MC was up to 22% (30.1 kJ g-1) with combustion time shortened by 1/6. SiO2-MC had a typical diameter of 150-210 μm, shell thickness of ∼6.5 μm, and a core fraction of 84 wt %. SiO2-MC showed better thermal stability with a higher initial evaporation/pyrolysis temperature than PUF-MC. The thermal decomposition of MCs with its mechanism of flame retardancy was significantly studied using thermogravimetric analysis/infrared spectrometry (TG-IR). The strategy presented in this study should inspire the development of microcapsules with PCMs/flame retardants as hybrid core materials for structural applications. Agency for Science, Technology and Research (A*STAR) Ministry of National Development (MND) The authors would like to acknowledge financial support from the Agency for Science, Technology and Research (A*STAR) -- Ministry of National Development (MND), Singapore (SERC132 176 0014).

As the scale of packages is increasing with the integrated devices on board, the stress, strain and damage induced by CTE (coefficient of thermal expansion) mismatch of package and substrate board dramatically enlarges during the process of thermal cycling test. Corner bond is a solution for the package performance since it can reduce the deformation of the system. In this work, the effect of interface behavior between the polymer material of the corner bond and the solder ball on the package reliability under a cyclic temperature loading was studied and demonstrated by a finite element model. The results show that a perfect bonding mechanism between the interfaces introduces another CTE mismatch followed by increasing stress and damage, while smooth interface behavior could avoid the issue by allowing for free deformation. This work offers suggestion on material selection and process design for the corner bond of BGA package.

Chalcogenide-based materials have attracted widespread interest in high-performance thermoelectric research fields. A strategy for the application of two types of chalcogenide for improved thermoelectric performance is described herein. Tin selenide (SnSe) is used as a base material, and Te nanoneedles are crystallized in the SnSe, resulting in the generation of a composite structure of SnSe with Te nanoneedles. The thermoelectric properties with various reaction times are investigated to reveal the optimum conditions for enhanced thermoelectric performance. A reaction time of 4 h at 450 K generated a composite Te nanoneedles/SnSe sample with the maximum ZT value, 3.2 times larger than that of the pristine SnSe. This result is attributed to both the reduced thermal conductivity from the effective phonon scattering of heterointerfaces and the improved electrical conductivity value due to the introduction of Te nanoparticles. This strategy suggests an approach to generating high-performance practical thermoelectric materials.

In this study, hollow glass bubbles (HGBs) of about 70 μm with through-holes of about 5 μm were successfully separated from a commercialized product and were used as targets to be sealed/covered by GO sheets of size about 24 μm. Firstly, these HGBs were treated with poly(ethyleneimine) (PEI) cross-linked polydopamine (PDA) to positively charge their outer surface. After treatment, the outer surface of HGBs was uniformly deposited with PDA nano-particles. During sealing/covering process, GO sheets were successfully attracted to the PDA modified HGBs by electrostatic force between the negatively charged GO sheets and positively charged HGBs introduced by the deposited PDA nano-particles, and were anchored by PDA nano-particles at the outer surface to avoid sucking of GO sheets into HGBs through the holes. While most of HGBs were tightly sealed/covered, some of them were partially sealed due to the fractured or collapsed GO sheets on the through-holes.

Twist has been well identified as an effective parameter to tune the mechanical behavior of carbon nanotube (CNT) fibers, e.g., tensile strength, strain, modulus and elastic-plastic behaviors. In this contribution, we uncover the twist-induced plastic deformation and failure behaviors of CNT fibers shrunk by ethanol (E-CNT fiber) and polyvinyl alcohol (P-CNT) solutions under low strain rate of 0.001 s−1 and high strain rate of 1300 s−1, which are essentially important for designing high-performance composites with respect to long term stability and short-term collision, respectively. It is found that the strain-induced microstructural evolution processes of CNT fibers depends on twist angle as a result of the strengthening effect of inter-CNT friction and the weakening effect of CNT obliquity. The tensile strength, failure strain and modulus of CNT fibers are more sensitive to strain rate as the twist angle increases. The optimum twist angle provides not only the higher tensile strength, but also the better data repeatability. The numerical results reveal that the brittle/ductile properties of filaments and their interfacial interaction will contribute to the plastic behaviors of a twist fiber. The empirical constitutive equations were built to describe the stress-strain curves of CNT fibers by taking the strain, helical geometry, twist-induced damage and strain rate into consideration.

Self-assembly strategies have been widely used to prepare aerogels from nanoparticles. It is challenging to assemble those nanoparticles whose surface is lack of abundant polar functional groups into aerogels, as the weak interface interactions among nanoparticles are not enough to maintain aerogel structures. Here we demonstrate a liquid extrusion strategy as a possible solution to this challenge, by using a small amount of large-sized graphene oxide and liquid extrusion devices. Large-sized graphene oxide sheets cover, wrap and assemble nanoparticles, and thus promote the assembly of nanoparticles. Extrusion devices are employed to control the shape and size of aerogels. Based on this strategy, a variety of nanoparticle, such as clay nanosheets, boron nitride nanosheets and carbon nanotubes, have been assembled into aerogels with designed shape and size even when there are few polar functional groups on nanoparticle surface. Detailed studies on clay aerogels show that the aerogels have porous structure and high performance, which can be proposed for applications in thermal insulation, fire retardation and absorption, etc. This liquid extrusion strategy can be thought of as effective, general and scalable approach to produce nanoparticle aerogels, particularly for those nanoparticles whose surface is lack of polar functional groups.

A new approach was developed to load 4,4′-bis-methylene cyclohexane diisocyanate in microcapsules, with outstanding stability in thermal and chemical environments, and excellent efficiency for both self-healing and self-lubricating uses. Well-dispersed microcapsules with diameter of 80 ± 22 µm and shell thickness of 3.8 ± 0.2 µm were produced with a core fraction of 74 ± 1.3 wt% as determined by titration. In thermal environments, the microcapsules started to lose 5% mass at 230 °C, which was higher than the boiling point of pure HMDI and thermal decomposition temperature of shell material. In chemical environments (hexane, xylene, ethyl acetate and water), the impermeable microcapsules reserved more than 90% of original core material after 20 days immersion. More interestingly, final microcapsules survived successfully in acetone losing only 25% of core material after 24 h. Parameters including microcapsules size, concentrations, immersion durations and solvent polarity were investigated systematically to obtain the stability of microcapsules in organic solvents. The smart coatings (10 wt% microcapsules) showed outstanding self-healing anticorrosion efficiency in sodium chloride solutions, and their friction coefficient decreased by 80% than control samples.

Materials that change color in response to external stimuli can cater to diverse applications from sensing to art. If made flexible, stretchable and weavable, they may even be directly integrated with advanced technologies such as smart textiles. A new class of engineered composite based on polydiacetylene (PDA) functionalized carbon nanotubes (CNT) shows tremendous potential in this regard. While the inherent multi stimuli chromatic response of the polymer (blue to red) is retained, the underlying conducting CNTs invoke electrochromism in PDA. Further, the fiber form factor of dry-spun CNT yarns facilitate direct weaving of large scale electrochromic fabrics, where current flow and thus color change can be accurately controlled. This review summarizes the fundamental aspects of CNT yarns and PDAs, focusing especially on their interaction chemistry which results in the scientifically and commercially appealing electrochromic transition in these hybrids.

Cheetah skin carbon nanotube, a novel periodically patterned nanocarbon on CNT synthesized as a highly effective filler for fabrication of high performance composites. The advantage of newly developed morphology lies in the fact that the size of nanocarbon on CNT and their distance can be fully controlled based on the application requirements. Cheetah skin CNT shows an excellent thermal stability and dispersibility in a high density polyethylene (HDPE) compared to pristine CNT/HDPE composite, making cheetah skin CNT a suitable candidate for fabrication of high performance HDPE based composite. The addition of cheetah skin CNT into HDPE resulted in a composite with improved thermomechanical properties. Compared with the pure HDPE and HDPE/pristine CNT, storage modulus and loss modulus of HDPE/cheetah skin CNT improved significantly at low temperatures even with very low content of cheetah skin CNT. Also, the thermal stability of the cheetah skin CNT/HDPE was found to be significantly higher than that of pristine CNT/HDPE composite in both isothermal and non-isothermal degradation performed for composites.

Healing is a vital factor of polymer materials. Herein, an investigation on the healing performance of Graphene-CNTs reinforced thermoplastic polyurethane (TPU) composites induced by microwave was carried out. The results show that the graphene sheet and CNTs formed a combined structure of Graphene-CNTs. This Graphene-CNTs may have a synergy effect on the coupling between microwave and Graphene-CNTs on the interface, and promote the fully healing of damaged composites. The tensile strength of the healed composites even exceeds the value of the virgin specimens. Simultaneously, there is a microwave focusing effect within the region of crack, and on the surfaces of graphene or CNTs that exposed on the fracture surfaces. This effect will also promote the healing of damaged composites, and can realize the preferential healing of crack as compared with the non-damaged regions. These results may help us to get a deeper understanding of healing mechanisms of some thermoplastic composites.

Encapsulation of polyamines for the practical application of self-healing epoxy is promising yet challenging due to their high reactivity and good solubility in water and most organic solvents. Herein, we developed an innovative method to directly synthesize microcapsules containing pure polyamine by integrating microfluidic emulsion and interfacial polymerization. Using this integration to make full use of the advantages and avoid the shortcomings of the involved two techniques, the properties of the fabricated microcapsules could be delicately tailored according to the practical demands of self-healing materials. The superiority of the obtained polyamine microcapsules was demonstrated via a dual-microcapsule high-performance self-healing system with fully autonomous recoverability, high thermal and long-term stability, relatively fast healing kinetics. The highest healing efficiency of 111 ± 12% in terms of recovered mode I fracture toughness was achieved at room temperature for 48 h without any external intervention. The high performance, environmental stability, and low cost and toxicity introduced by the robust microcapsules promote the potential practical application of this self-healing system.

The interfaces between the composite and metal in fiber metal laminates (FMLs) are vulnerable to the attacks of moisture and heat. Two surface treatment methods are introduced to improve the interlaminar performance of the FML made of titanium alloy (Ti) and carbon fiber-reinforced polymer (CFRP). The FML prepared using the anodized Ti plate and CF sheets grafted with multiwalled carbon nanotubes shows significantly increased interlaminar fracture toughness (1382%), compared with the FML fabricated with sandblasted Ti plate and untreated CF sheets. The exposure to long-term hygrothermal environment, i.e. 60-day immersion in simulated seawater at room temperature, reduces the performance of both treated and untreated FMLs. However, the treated maintains the improvement of interlaminar performance, and shows much higher interlaminar fracture toughness (25.5 times) than the untreated. This study provides a feasible solution to tune the interlaminar properties of the FMLs based on titanium alloy and carbon fibers for industrial applications.

Controlling the molecular assembling and nanomorphology of organic semiconductors is crucial to obtain high-performance electronic devices. In this work, we have first reported novel superlong salicylideneaniline nanobelts (mHBA) using the magnetic nanoparticle-assisted self-assembly process. Our results show that magnetic nanoparticles will obviously influence the self-assembly behavior, nanomorphology, and crystal structure of molecular HBA. Moreover, the intensity of fluorescence mHBA exhibits decreasing and increasing patterns, with the increase in temperature over a wide temperature range of 8 to 295 K. To elucidate the origin of tautomer forms, the ground and excited states of mHBA were experimentally and theoretically studied. Our results suggest that superlong HBA nanobelts provide a promising intelligent fluorescent thermometer and an organic field-effect transistor.

The planing trimaran possesses distinctive hybrid hydrodynamic and aerodynamic performance due to the presence of tunnel. The research described in this paper was carried out based on the observation of wave characteristics of a planing trimaran model in towing tests, in which the resistance drops as soon as the wave surface separates from tunnel roof. In order to gain a deeper insight into the relationship between wave flow and forces in tunnel region, a comprehensive series of viscous CFD simulations considering free-surface and 2-DOF motion of the hull (heave and pitch) have been performed for the tested model at the volume based Froude numbers ranging from 3.16 to 5.87. The calculated results were validated by comparison with experimental data and showed good agreement. Numerical results of wave contours, longitudinal wave cuts and lifting force distributions at the calculated speeds were presented for the analysis of ventilation process in tunnel region and the corresponding variation of tunnel forces. It is found that, for the speeds higher than Froude number of 4.52, the aerodynamic forces provide major tunnel lift and mainly act on the straight section of the tunnel. And, therefore, numerical simulations of two modified models have also been performed for the analysis of influence of straight section length on the hydrodynamic and aerodynamic performance of planing trimaran.

Unstable crack propagation behavior of carbon fiber reinforced plastic (CFRP) composites has a significant impact on the safety and reliability of structures in practical applications. Herein, we reported a method to improve the stability of crack growth by coating polydopamine (PDA) and graphene oxide (GO) on the surface of carbon fabric. The Mode I and Mode II tests were performed to study the delamination and crack behaviors of pure CFRP and modified CFRP. The crack propagation behavior can be tuned from unstable to stable manner without sacrificing the crack initiation during the opening mode test. It was revealed that the crack tended to fracture through the GO sheets, leading to the tearing and peeling of GO. The PDA&GO coated layers contributed to improving the load transfer between carbon fibers and polymer matrix, reducing the crack blunting degree, minimizing the unstable crack growth, and thus dissipating more energy. Keywords: Polydopamine, Graphene oxide, Carbon fiber reinforced plastic, Fracture toughness, Crack propagation

Herein, we report a smart coating with autonomous self-healing and self-reporting functions by simple integration of one-component microcapsules into the matrix without external intervention. The microcapsules containing hexamethylene diisocyanate (HDI) solution of aggregation-induced emission luminogens (AIEgens) were synthesized, and their properties, such as their composition, thermal stability, morphology, and damage-indicating ability, were investigated systematically. The AIEgen/HDI microcapsule-embedded coatings display adaptive self-repair of scratches and simultaneous high-contrast indication of the healed damage. Two commercialized AIEgens, tetraphenylethylene (TPE) and its derivative with dimethoxyl and benzylidene-methyloxazolone moieties (DM-TPE-BMO), were utilized as examples to demonstrate the feasibility of this concept in diverse polymer matrixes (including blue autofluorescent matrixes). It was found that the content of AIEgens can even be lowered to 0.05 wt %. This facile, economical, and feasible strategy toward the dual functions of self-repairing and self-sensing provides a new route for enhancing the longevity and reliability of polymer coatings, which is appealing and of great importance in practical applications.

Continuous shrinking of VLSI technology nodes brings us powerful chips with lower power consumption, but it also introduces many issues in manufacturability. Lithography simulation process for new feature size suffers from large computational overhead. As a result, conventional mask optimization process has been drastically resource consuming in terms of both time and cost. In this paper, we propose a high performance machine learning-based mask printability evaluation framework for lithography-related applications, and apply it in a conventional mask optimization tool to verify its effectiveness.

Corrosion and biofouling are two common unsolved problems in the marine industry, urging the need of innovative solutions to tackle both problems simultaneously. Herein, the fabrication of multifunctional microcapsules containing 8-hydroxyquinoline (8-HQ)as the corrosion inhibitors and clove oil as the natural antimicrobial compound is described to resolve both corrosion and biofouling problems simultaneously. Microcapsules containing 8-HQ and clove oil, featuring good mechanical properties, anticorrosion, and antibacterial properties, were successfully synthesized through in-situ polymerization of melamine-formaldehyde polymer. The fabricated microcapsules show antibacterial properties against Escherichia coli, Vibrio coralliilyticus and E. aestuarii, as revealed from the standard ASTM E2315 time-kill test. Multifunctional coatings with both antibacterial and anticorrosion features were fabricated by incorporating the fabricated microcapsules both onto and into the epoxy coatings. According to the zone inhibition test, the microcapsules-based multifunctional coating possesses antibacterial properties against the seawater bacteria. Manually scratched microcapsules-based multifunctional coatings possess anticorrosion properties, due to the formation of corrosion inhibition layer resulted from the reaction between the released 8-HQ compound and the mild steel substrate. Additionally, after 30 days of immersion in the salt water, the microcapsules-based coatings still possess anticorrosion properties by forming corrosion inhibition layer at the scratched region. Nanyang Technological University We are grateful to the support partially from the Hong Kong University of Science and Technology (Grant #: R9365). Chong acknowledges the research scholarship support from NTU.

Robustness of microcapsule shells determined the service life and application areas of final smart materials including self-healing composites, anticorrosion coatings, smart concretes, and so on. Herein, we designed and synthesized metal microcapsules by conducting electroless plating directly on liquid droplet surfaces, and metal shells showed superior stability in thermal (600 °C) and polar solvents (acetone and N,N-dimethylformamide) environments. More interestingly, the mechanical strength of metal shells was ten times higher than those of all published microcapsules. Besides, the smart epoxy composites remained stable mechanical properties with metal microcapsule concentrations, and this is the first time to report such results. For engineering materials, mechanical properties played an important role in practical applications, and a higher strength usually accompanied with better safety and longer service life. The microcapsules with designable structures could be synthesized by adjusting shell thickness and core fractions for practical requirements. The metal microcapsules had great potentials to be applied in a smart metallic matrix, conductive multifunctional materials, and pH-responsive materials. In addition, the electroless plating technique was also first applied to liquid surfaces pushing the development of novel smart materials. This work was supported by the Startup Fund from HKUST (grant no. R9365).

Despite wide applications of reduced graphene-oxide (GO)-reinforced polymer-based composites, the necessity of the reduction procedure toward GO is still controversial. In this article, thermoplastic polyurethane (TPU) composites incorporated with GO and thermally reduced graphene oxide (TGO) were fabricated. GO and TGO exhibited different effects on crystallization behaviors, and mechanical and thermal properties of the TPU matrix. With 2.0 wt % filler loading, TPU composite reinforced by GO (TPU-GO-2 wt %) exhibited better thermal stability than that reinforced by TGO (TPU-TGO-2 wt %). The interfacial interaction between the nanofillers and the TPU matrix as well as their influence on the mobility of TPU chains were investigated, which proved that GO is superior to TGO in improving interface adhesion and maintaining crystallization of the TPU matrix. Compared with TPU-TGO-2 wt %, improved mechanical properties of TPU-GO-2 wt % were also evidenced owing to more oxygen-containing groups. This work demonstrates that the reduction of GO is not always necessary in fabricating polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47745. The authors acknowledge financial support from the Start-upGrant from HKUST (R9365) and the Natural Science Foundationof China (Grant No. 51703248)

This study investigates the effects of fiber type, resin type, and stacking sequence on the dynamic response of fiber-reinforced polymer composite (FRPC) laminates under low-velocity impact (LVI) tests. Novel thermoplastic (TP) laminates are fabricated with a newly developed liquid methyl methacrylate thermoplastic resin, Elium® 188, at room temperature. FRPCs comprising woven ultra-high molecular weight polyethylene (UHMWPE) fabrics, woven carbon fabrics, and two different hybrid systems with alternative stacking sequences of those fibers are fabricated by the vacuum-assisted resin infusion (VARI) method. Besides, equivalent thermosetting-based (TS) composites with two epoxy systems are fabricated to compare the role of matrix type. Impact tests at different energy levels are performed on the TP and TS laminates to investigate the impact characteristics, namely contact force, deflection, energy attributes, structural integrity, and failure/damage modes. Besides, the mechanics of structure genome (MSG) and the commercial finite element code ABAQUS are used to verify the experimental results for one of the developed laminates. The results demonstrate that the hybrid system with UHMWPE fibers on the sides exhibits lower structural loss up to 47% and lower absorbed energy by 18% compared to those presented by the other type of hybrid system comprising carbon fabrics on the sides. Besides, it is found that the newly developed TP laminate underwent extended plasticity and presented a ductile behavior. The newly developed TP laminate demonstrated lower structural loss up to 200%, lower contact force by 14%, and lower absorbed energy by 48% compared to those of TS counterparts.

Reducing filler content in microwave-absorbing composites is of great significance and challenging. Via a facile dip-coating method followed by a pyrolysis process, a new type of melamine foam (MF) derived carbon aerogel with in situ grown nitrogen-doped carbon nanotubes was fabricated, without using any externally introduced carbon source. Owing to the formed hierarchical and cellular structures, the prepared composites impregnated with epoxy (MF@GMC/epoxy) exhibit excellent microwave-absorption performance at a low filler ratio. The minimum reflection loss of a 3 mm MF@GMC/epoxy sample reaches −47.5 dB at 12.20 GHz. The effective absorption bandwidth achieves 6.72 GHz (9.22–15.94 GHz) while the filler loading is only 1.3 wt%. The development of MF@GMC/epoxy may pave a new avenue for the high-efficiency microwave absorption materials with extra-low filler loading.

Linear two-dimensional materials have recently attracted an intense interest for supercapacitors because of their potential uses as electrodes in next-generation wearable electronics. However, enhancing the electrochemical properties of these materials without complicated structural modifications remains a challenge. Herein, we present the preparation of a hybrid electrode system via polydiacetylene (PDA) cloaking on the surface of aligned multiwall carbon nanotubes (MWCNTs) through self-assembly based in situ photopolymerization. This strategy eliminates the need for initiators and binders that hinder electrochemical performance in conventional conducting polymer based composite electrodes. As noncovalent PDA cloaking did not alter the chemical structure of MWCNTs, high inherent conductivity from sp2 hybridized carbon was preserved. The resulting hybrid microfiber (MWCNT@PDA) exhibited a significant increase in specific capacitance (1111 F g–1) when compared to bare MWCNTs (500 F g–1) and PDA (666.7 F g–...

Dispersion systems such as solutions, suspensions and composites are frequently studied in the field of graphene and two-dimensional materials. The rapid development of these materials demands comprehensive insight into their dispersion systems. Here we present an innovative and systematic investigation on the dispersion systems of graphene-like two-dimensional materials. It is found that different dispersion systems exhibit similar fundamental laws which can be described based on a Most Probable Percolation Threshold (MPPT) theory. Two-dimensional sheets contact with their neighboring ones at around their MPPT concentrations and thus lead to sudden changes in various properties of dispersion systems, such as liquid crystal behavior, viscosity, mechanical strength, electrical conductivity and thermal properties. Starting from the MPPT theory, six new strategic guidelines for the engineering of dispersion systems are established. Based on these studies, we find that, appropriate size, appropriate thickness, and appropriate concentration, are the keys to the success of 2dMs dispersion systems in practical applications, and the MPPT theory could tell where it is appropriate. These investigations provide new theories, methodologies and guidelines for the science, engineering and developments of graphene and two-dimensional materials.

Weavable color-change materials are useful in smart textiles. Here we demonstrate static and programmable color change on flexible polydiacetylene (PDA) coated carbon nanotube (CNT) yarns through 3D hopping-conduction-induced electrochromism. The color change could be achieved using pre-patterning and further specified through defining the current paths. Mild heating before polymerization was used to gain control over the critical transition voltage and ZnO nanoparticles were introduced to anchor PDA and facilitate reversibility of the electrochromic transition. In-situ absorbance and Raman spectroscopy, Raman mapping and surface characterization with X-ray spectroscopy revealed that mild heating increased the critical transition voltage while PDA anchoring on ZnO improved the reversibility. The ability to tune CNT/PDA electrochromism through inexpensive structural alterations is promising for applications in smart textiles where complex patterns can be instantaneously realized and controlled with electrical stimulus.

Hollow Glass Microspheres (HGM) filled polymers are widely used in marine, aerospace and civil engineering. In this work, the mechanical properties of HGM filled polymers were investigated under low strain rate tests for compressive and tensile behaviors, and high strain rate tests for compressive behaviors. Systematic investigations are carried out to study the mechanical responses, energy absorption and failure modes of HGM filled polymers with different volume fractions of glass microspheres subject to different loading conditions. HGM filled polymers showed strong strain rate effect and the strain rate sensitivity factor increased with the increase of strain rate while decreased with the increase of filler volume fraction. HGM filled polymer absorbed more energy at Vf around 7.5% under low strain rate compression. Different fracture modes were discovered for HGM filled polymers under low and high strain rate loadings by using Computed Tomography (CT) scan and Scanning Electron Microscope (SEM). The numerical results obtained from finite element analysis fitted well with the experimental data. In addition, a convenient generalized model was proposed to depict and predict the compressive strength of HGM filled polymers in the observed range of strain rates.

Rate-dependent mechanical properties of individual carbon nanotube (CNT) fibers are essential for developing advanced anti-collision composites. In this work, a free-falling Hopkinson tension bar was designed to measure the dynamic tensile strength of CNT fiber. The strength of pure CNT fiber is found to be more sensitive to strain rate than that of composite CNT fiber. The dynamic failure morphologies of pure and composite CNT fiber were compared with their quasi-static responses. It was observed that the pure CNT fiber tends to break off at the weakest point, leading to unraveling of fiber along the twisted direction. On the other hand, the infiltrated polymer tends to change the failure mode and rate sensitivity of CNT fibers. Furthermore, high speed deformation analysis under dynamic loading revealed that pure CNT fiber tends to fail at the weakest point while the composite CNT fiber breaks into several fragments.

In order to get a strong Ti-epoxy bond, nano-silica was added to epoxy as the reinforcement, and the effects of the presence of nano-silica on the properties of epoxy nanocomposites and Ti-epoxy assembles were investigated. The results showed that, although glass transition temperature of nanocomposites decreased with the increase in silica addition, mechanical properties of the nanocomposites such as flexural strength, fracture toughness, and hardness rose to the highest values when silica content was 15 wt%. However, the shear strength of the Ti-epoxy assemble was 45.38 MPa when the silica content was 2.5 wt%, from a low of 31.75 MPa for pure epoxy bonded assemble, increasing by 42.9%. With further increase in silica content, the shear strength decreased gradually. The remarkable increase in the shear strength with 2.5 wt% silica addition should be attributed to the improved wettability between epoxy and Ti surface, which resulted in much higher bonding strength between them.

Double-shelled microcapsules containing liquid 4,4′-bis-methylene cyclohexane diisocyanate (HMDI) with outstanding water resistance are successfully synthesized via combination of interfacial and in-situ polymerization reactions in an oil-in-water emulsion. The diameter and shell thickness of microcapsules increased under lower agitation rate. The relative residue of core content of microcapsules remains more than 90% after 24 days in both ambient open air and water. Manually scratched polymer coatings with both fresh and conditioned microcapsules showed satisfactory anticorrosion performance in salt water via self-healing functionality. In addition, self-healing coatings with fresh microcapsules after immersion in ambient water for 30 days still possessed superior anticorrosion performance.

We report the first use of spark plasma sintering (SPS) as a single-step process to achieve superhydrophobic reduced graphene oxide (rGO). It was found that SPS was capable of converting smooth and electrically insulating graphene oxide (GO) sheets into highly electrically conductive rGO with minimum residual oxygen and hierarchical roughness which could be well retained after prolonged ultrasonication. At a temperature of 500 °C, which is lower than the conventional critical temperature for GO exfoliation, GO was successfully exfoliated, reduced, and hierarchically roughened. rGO fabricated by only 1 min of treatment at 1050 °C was superhydrophobic with a surface roughness (Ra) 10 times as large as that of GO as well as an extraordinarily high C:O ratio of 83.03 (atom %) and water contact angle of 153°. This demonstrates that SPS is a superior GO reduction technique, which enabled superhydrophobic rGO to be quickly and effectively achieved in one single step. Moreover, the superhydrophobic rGO fabricated by SPS showed an impressive bacterial antifouling and inactivation effect against Escherichia coli in both aqueous solution and the solid state. It is envisioned that the superhydrophobic rGO obtained in this study can be potentially used for a wide range of industrial and biomedical applications, such as the fabrication of self-cleaning and antibacterial surfaces. Accepted version

Contributed by the highly reactive, antibacterial, and readily reducible polyethylenimine (PEI), polyurethane (PU) composites incorporated with slightly reduced graphene oxide (SRGO) modified with PEI (SRGO-PEI) were prepared by in situ polymerization. X-ray photoelectron spectroscopy confirmed that SRGO-PEI was only slightly reduced under mild reducing conditions, because the carbon-to-oxygen atomic ratios increased slightly, from 2.56 to 4.00. The Fourier transform infrared spectra and the results of X-ray diffraction indicated that the PEI on SRGO-PEI were not only covalently grafted but also intercalated into SRGO interlayers. The mechanical properties and thermal stability of PU/SRGO-PEI were highly enhanced because of the chemical bonds formed between SRGO-PEI and PU matrices. With the incorporation of 1.0-wt% SRGO-PEI, the elongation at break, tensile strength, and Young's modulus of PU/SRGO-PEI increased by 32.7%, 251.1%, and 172.7%, respectively. Moreover, the adhesion of bacteria on functionalized GO/PU composites was reported for the first time. The PU/SRGO-PEI composites exhibited enhanced bacterial antiadhesive property when compared with that of pure PU and PU/GO. This desirable antibacterial property of SRGO-PEI is proposed to be mainly contributed by the presence of high-density amine groups in the PEI chains.

Spills or leakages of hazardous chemicals involve high safety, health and environmental risks. Absorption of hazardous chemicals using absorbent materials is an advanced and efficient strategy for cleaning up hazardous chemical spills. Here, we report a new form of carbon-based macrostructure, graphene oxide beads with core/shell structures, for fast clean-up of hazardous chemicals. Graphene oxide beads are produced by one-step self-assembly of graphene oxide in a coagulation bath. The core of the beads is graphene oxide foam, while the shell is a graphene oxide membrane. The amphipathic and porous core provides a large absorption capacity for a broad range of hazardous chemicals. By incorporating layered silicates, graphene oxide beads become highly fire retardant, hence are especially suitable for cleaning up chemicals with accompanying fire risks. The millimeter-level size and spherical morphology of the beads offer high convenience in practical usage. Moreover, the beads can also be used in many other applications, such as heat energy storage and sustained release.

The concentration of glucose in biological fluids is in the micromolar range, the detection of which requires devices with high sensitivity and low limit of detection (LOD). Here, we report the real-time electronic detection of glucose using an antioxidant found in green tea, namely, epigallocatechin gallate (EGCG), decorated on carbon nanotubes (CNTs) and tested in a chemiresistor configuration. The detection principle relies on the spontaneous reaction of EGCG with hydrogen peroxide, a reactive oxygen species released during glucose oxidation, which is translated electrically as a change in CNT conductance. Our results suggest that the response of EGCG decorated CNTs was far superior to that of the bare CNT based device. The sensor detected glucose ranging from 10 nM to 1 μM with LOD of ∼8.7 nM, which is much lower than the commercially available finger-pricking based glucose sensors. This could pave the way for developing simple resistivity-based sensors capable of glucose detection in biological fluids other than blood, such as sweat and saliva. MOE (Min. of Education, S’pore)

Photoactive materials that are triggered by the irradiation of light to generate an electrical response provide an ecofriendly platform to afford efficient power sources and switches. A chemical assembly of well-known elements with aligned carbon nanotube bundles is reported here, which was employed to form an efficient photo-induced charge transfer device. The primary elements of this device are ultra-long multi-walled carbon nanotube (MWCNT) bundles, polyaniline (PANI) thin film coating, and CdSe quantum dots (QDs). Highly ordered and horizontally aligned MWCNT bundles were coated with PANI to enhance charge transfer properties of active QDs in this platform. The obtained device (CdSe-MWCNT@PANI) constructed on a silicon base exhibits highly efficient power conversion capabilities owing to the aligned MWCNT bundle assisted enhanced charge transport pathways generated within the device. The device also shows a short circuit current density (Jsc) of 9.81 mA cm(-2) and an open circuit voltage (Voc) of 0.46 V. The power conversion efficiency (PCE) of the device is 5.41%, and the current response is quite stable, highly responsive, and reproducible.

Thermoplastic fiber-reinforced polymer (FRP) composites play a significant role in industrial applications due to their high energy absorbing capability. Combining ultra-high-molecular-weight polyethylene (UHMWPE) fiber/fabric and infusible thermoplastic methyl methacrylate (MMA) based matrix forms a complete thermoplastic composite system, which can fulfil the demands of being lightweight and high energy absorption during an impact loading. Among many different parameters, the interfacial bonding strength between fiber and matrix plays an important role in determining the impact performance of a composite system. In this study, the interfacial bonding strength between UHMWPE fibers and MMA thermoplastic matrix is improved by a simple deposition of polydopamine (PDA) surface treatment (on the fiber surface) with the addition of 0.03 wt% of functionalized multiwalled carbon nanotubes (MWCNT). Experimental investigations were carried out to determine the low-velocity impact behavior on the pristine and PDA surface-treated thermoplastic composites at three different impact energies of 26 J, 32 J, and 50 J. The results after the impact test revealed that PDA and PDA with MWCNT fiber surface-treated composites offer less structural damage, thanks to the improved delamination resistance at the fiber and matrix interface when compared to that of the pristine composite at all different impact energies.

In the current study, the mechanical characteristics of a new generation of thermoplastic fiber metal laminates (FMLs) manufactured by vacuum-assisted resin infusion (VARI) at room temperature are investigated. For this end, Ti-6Al-4V alloy sheets, ultra-high molecular weight polyethylene (UHMWPE) fabric, carbon fabric, and two hybrid laminates with different layups are manufactured by a novel liquid methyl methacrylate (MMA) thermoplastic resin, Elium®. Prior to fabricating and testing, a multi-step surface treatment is followed to improve the bonding strength between the titanium alloy sheets and fiber-reinforced polymer composite (FRPC) laminates. ASTM standard tests are conducted in tension, compression, shear (both intralaminar and interlaminar) as well as flexural to evaluate the mechanical characteristics of the newly developed hybrid titanium composite laminates (HTCLs). The results are compared with those of equivalent monolithic composites as well as traditional FMLs in the literature to determine the possibility of replacing epoxy resins with Elium® for fabricating different types of FMLs, namely HTCLs. In addition, the results are verified by a recently developed homogenization method, that is the mechanics of structure genome (MSG), which is used in parallel with the rule of mixture (ROM) to verify the experimental results of HTCLs and their constitutive FRPC laminates. The results show equivalent mechanical properties of the newly developed HTCLs compared to those of traditional thermoplastic HTCLs with the advantages of fabricating at room temperature, increasing the production rate, eliminating the residual thermal stresses, and the requirement for post-stretching HTCL panels.

As the operating speed and efficiency of electronic devices increase continuously, developing their thermal management and electromagnetic shielding capabilities has become extremely important. In this study, we prepared a paraffin wax/carbon nanotube sponge (PW@CNS) composite with simultaneous high-efficient thermal management and electromagnetic interference shielding functions via the simple vacuum impregnation method. The PW component functions as the phase change working substance for thermal management applications, and whereas the three-dimensional electrically conductive CNS component forms the matrix supporting the PW and a shielding structure against electromagnetic waves. The properties of PW@CNS are characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Its latent heat and relative enthalpy efficiency during melting and freezing process are as high as 248.8 J/g and 247.7 J/g, and 96.2% and 96.3%, respectively. After 100 thermal cycles, the latent heat remained nearly constant, and the prepared PW@CNS exhibited the excellent thermal management behavior and electromagnetic interference (EMI) shielding effectiveness (SE). All the results indicate that this PW@CNS has great potential as a thermal management and electromagnetic interference shielding material for electronic devices.

It is a great challenge to develop a scalable and cost-effective strategy for fabricating porous polymer-based piezoresistive devices. Here we presented a sort of conductive porous thermoplastic urethane (TPU) composites incorporated with carbon nanotubes by a vapor-induced phase separation method. By the introduction of carbon nanotubes (CNTs), the TPU composite exhibits moderate electric conductivity and improved compressive property. TPU composites are demonstrated to be highly sensitive sensors for monitoring both compression and bending strain. The value of ΔR/R0 changed from 90.0 to 98.7% while the gauge factor varied from 1.98 to 9. Further study on the dynamic mechanical performances indicates the produced TPU composites are strain-rate sensitive and the addition of CNTs can improve the anti-impact performances of TPU foam. The strategy adopted to fabricate TPU/CNT composite will pave the way for the development of low-cost and wearable sensors in practical applications of health monitor and sports.

Polymeric materials are susceptible to the chain re-conformation, reorientation, slippage, and bond cleavage upon mechanical stimuli, which are likely to further grow into macro-damages and eventually lead to the compromise or loss of materials performance. Therefore, it is of great academic importance and practical significance to sensitively detect the local mechanical states in polymers and monitor the dynamic variations in polymer structures and properties under external forces. Mechanochromic fluorescent polymers (MFP) are a class of smart materials by utilizing sensitive fluorescent motifs to detect polymer chain events upon mechanical stimuli. Taking advantage of the unique aggregation-induced emission (AIE) effect, a variety of MFP systems that can self-report their mechanical states and mechano-induced structural and property changes through fluorescence signals have been developed. In this feature article, an overview of the recent progress on MFP systems enabled by AIE process is presented. The main design principles, including physically doping dispersed or microencapsulated AIE luminogens (AIEgens) into polymer matrix, chemically linking AIEgens in polymer backbones, and utilizing the clusterization-triggered emission of polymers containing nonconventional luminogens, are discussed with representative examples. Perspectives on the existing challenges and problems in this field are also discussed to guide future development.

Bionic structural material is a new type of high-performance material that has promising applications in the fields of aerospace, bio-medicine, etc. Herein, an investigation on the easy scale-up process and mechanical behavior of large-sized three-dimensional graphene oxide-based bioinspired nacre bulk materials with excellent mechanical properties was carried out. These bulk materials could be prepared by a lamination assembly strategy based on mass of two-dimensional graphene oxide nacre-mimetic films that fabricated by the continuous dry-spinning assembly technology. The mechanical mechanisms analysis showed that the lamination assembly process could control the interface bonding, and regulated the interface load transfer and failure models of the hierarchical structures, then optimized the combination of strength and energy absorption of the materials to meet different application requirements. These results may provide useful guidance for the efficient and controllable production of high-performance artificial nacre structure materials in application.

Thermoplastic fiber metal laminate (T-FML) is a new hybrid composite material, which is a combination of sandwiched metal and complete thermoplastic fiber reinforced polymer (FRP). Due to its superior properties contributed from the unique combination of metal and FRP's, it has been applied in various advanced fields, like aerospace, and automotive. However, poor adhesion between inhomogeneous material surfaces of fiber, metal, and matrix in T-FML makes the whole system weaker. In this work, the Ti6Al4V (titanium alloy) and ultrahigh molecular weight polyethylene fiber (UHMWPE) reinforced thermoplastic (Elium®) polymeric composite were combined together to form a T-FML. Fiber surface functionalization by PDA (polydopamine) coating with MWCNT (Multiwalled carbon nanotubes) has been adopted to enhance the bonding between the fiber and matrix. Ti6Al4V metal surface treatment by anodization with postprocessing of etching and annealing process has been adopted to enhance the interfacial bonding between metal thermoplastic composite interface (MTCI). The double cantilever beam test was utilized to evaluate the G1C (Mode I interlaminar fracture toughness at MTCI) for the T-FML sample with fiber surface functionalization and metal surface treatment. The result shows, after metal surface treatment, the average G1C can be immediately increased from 0.25 kJ/m2 (pristine titanium alloy with pristine fiber) to 1.57 kJ/m2 for surface-treated titanium alloy with pristine fiber. The PDA only coating for UHMWPE fiber enhanced the G1C from 1.57 kJ/m2 to 1.84 kJ/m2. PDA fiber surface functionalization with MWCNT coating enhanced the G1C further to 2.54 kJ/m2.

This paper reviews fiber metal laminates (FMLs) with a focus on hybrid titanium composite laminates (HTCLs). FMLs are high-performance hybrid structures based on alternating stacked arrangements of fiber-reinforced polymer composite (FRPC) plies and metal alloy sheets. The mechanical performance potential of FMLs inspired an investigation into new composites, metals, and adhesive systems to further improve their mechanical properties and to reduce the weight of these structures. HTCLs offer better advantages when compared to traditional FMLs and FRPCs, especially in aeronautical, marine, military, and offshore applications both at room and elevated temperatures as well as harsh environmental conditions. They are outstanding in terms of stiffness, yield stress, fatigue, and high-velocity impact properties; however, there are some challenges regarding fabrication, surface treatment, and mechanical properties of such structures, which need to be further addressed. Due to the lack of consolidated research surrounding HTCLs, a review is necessary for effective comparison.