Improved organic-inorganic/graphene hybrid composite as encapsulant for white LEDs: Role of graphene, titanium (IV) isopropoxide and diphenylsilanediol Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-21 P. Madhusudhana Reddy, Chi-Jung Chang, Chun-Feng Lai, Min-Ju Su, Mei-Hui Tsai
Surface modification of PBO fibers by direct fluorination and corresponding chemical reaction mechanism Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-21 Longbo Luo, Dawei Hong, Lingjie Zhang, Zheng Cheng, Xiangyang Liu
Due to their excellent mechanical properties and heat resistance, Poly(p-phenylene benzobisoxazole) (PBO) fibers are applied as one of most potential reinforcement in resin matrix composite. However, the poor adhesion with resin limits their application in advanced composite materials. In this study, PBO fibers were first modified by direct fluorination to improve the interface adhesion between fibers and resin. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to characterize the change of chemical structure and surface topography of fluorinated fibers. The results show that polar groups of C-F and -COOH are produced and surface roughness is enhanced, which increases the interface bonding strength of PBO fibers/epoxy by 48%. The fluorination reaction mechanism of PBO fibers is investigated on the basis of chemical structure change. It's suggested that oxazole ring reacts with fluorine gas preferentially over benzene ring, and addition reaction dominates when fluorine reacts with benzene ring.
Chemical vapor deposition-based grafting of CNTs onto basalt fabric and their reinforcement in epoxy-based composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-19 Garima Mittal, Kyong Y. Rhee
Basalt fiber (BF) is considered to be a green industrial material, exhibiting outstanding environmental stability along with superior mechanical properties compared to E-type glass fiber. It is also less expensive than carbon fiber, making make it perfect for the mass-production of basalt fiber-reinforced polymer (BFRPs) composites. BFRPs are reinforced with nanomaterials to further enhance their performance. However, nanomaterials have the tendency to agglomerate because of their high surface energy, which hinders their efficient dispersion into the matrix. Hence, in this study, we grafted CNTs onto basalt fabric using chemical vapor deposition (CVD). Furthermore, CNT-grafted basalt fabric (BF-CNT) was sandwiched with epoxy via a hand lay-up technique. XRD, HR-RAMAN, FE-SEM, and thermogravimetric analysis (TGA) were performed to characterize BF-CNT. The properties of the fabricated BF-CNT/epoxy composites were also analyzed and compared with CNT-reinforced BF/epoxy composites. Based on our results, we found that the BF-CNT/epoxy composite shows improved properties.
The effect of polymer particle size on three-dimensional percolation in core-shell networks of PMMA/MWCNTs nanocomposites: Properties and mathematical percolation model Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-15 Seung Han Ryu, Hong-Baek Cho, Seil Kim, Young-Tae Kwon, Jimin Lee, Kee-Ryung Park, Yong-Ho Choa
Segregated highly conductive percolation networks in nanocomposites consisting of a polymethyl methacrylate (PMMA) core and multi-walled carbon nanotube (MWCNT)-shell were investigated experimentally as a means of exploring the relationship between the micro-dimensional size of spherical polymer particles and the number of coated MWCNT layers by a new theoretical approach of filler monolayer model. The measured electrical conductivity of the core-shell structured complex utilizing 20 μm PMMA spheres showed that percolation was achieved at a very low filler content of 0.0099 wt% MWCNTs, whereas 0.149 wt% MWCNT was required to achieve percolation when 5 μm PMMA spheres were utilized. The size of PMMA cores was attributed to the percolation threshold, and conductivity was enhanced by increased layers of MWCNT coating. The percolation behaviors based on the theoretical model and experimental data were elucidated. Furthermore, an advanced theoretical model for prediction of number of MWCNT monolayers was provided.
Uniformly dispersed polymeric nanofiber composites by electrospinning: Poly(vinyl alcohol) nanofibers/polydimethylsiloxane composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-15 Kentaro Watanabe, Tomoki Maeda, Atsushi Hotta
A method for the fabrication of homogeneous and well-dispersed polymeric nanofiber composites was investigated. Nanofiber fillers can be used to produce polymeric nanocomposites by mixing the fillers to base polymers, eventually enhancing the mechanical property of the matrix polymers. To produce such composites, nanofibers were usually sandwiched by molten matrix polymers at high temperature before molding. The traditional so-called sandwich method, however, was found to produce rather biased and inhomogeneous composites due largely to the solid entanglement of the nanofibers. In this work, unwoven polymer nanofibers were synthesized through electrospinning by controlling the electrostatic repulsion of the nanofibers. We modified the electrospinning apparatus for the direct synthesis of homogenous composites: nanofibers were electrospun and directly ejected from the electrospinning syringe to the matrix polymer solution (not in a solid state), where a regular metal electrode plate was replaced by an optimized metal container containing the base polymer solution. It was found that this new fabrication method could realize homogeneous mixing of the nanofibers that were eventually uniformly dispersed in the polymer solution. Poly(vinyl alcohol) (PVA) was used for nanofibers and polydimethylsiloxane (PDMS) was used for polymer matrix. The field emission scanning electron microscopy (FE-SEM) revealed the homogeneous and well-dispersed PVA nanofibers in the resulting PDMS composites. The composites also presented higher mechanical properties as compared with the composites fabricated by the traditional sandwich method.
Fabrication of a piezoelectric polyvinylidene fluoride/carbonyl iron (PVDF/CI) magnetic composite film towards the magnetic field and deformation bi-sensor Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-15 Min Sang, Sheng Wang, Mei Liu, Linfeng Bai, Wanquan Jiang, Shouhu Xuan, Xinglong Gong
In this paper, a versatile polyvinylidene fluoride/carbonyl iron (PVDF/CI) composite film was prepared by doping magnetic carbonyl iron (CI) particles into piezoelectric polyvinylidene fluoride (PVDF) matrix. Without influencing the piezoelectric structure of PVDF, CI particles enhanced the Young's modulus and maximum tensile strength of composite films. Due to the magnetic driven characteristic, PVDF/CI composite films exhibited distinct magnetic-mechanic-electric coupling properties. The piezoelectric charge signals could be generated by applying the bending deformation or magnetic field. Taking PVDF/CI-10% (CI content was 10 wt%) film as an example, the piezoelectric charges under 2, 4, 6, 8, and 10 mm bending displacement were 3.0, 9.6, 14.9, 18.6, and 24.6 pC respectively. Moreover, when the magnetic field varied from 0 to 600 mT, the generated magneto-electric charges of PVDF/CI-10% film increased from 0 to 676 pC. The quantitative relationship between magnetic field and magneto-electric charges was obtained by the polynomial fitting method and the correlation coefficient was up to 0.97. Owing to the high piezoelectric coefficient, excellent stability, light weight and desirable flexibility, PVDF/CI composite films showed promising applications in deformation sensor and magnetic field sensor.
Experimental determination of Through-Thickness Compression (TTC) enhancement factor for Mode II fracture energy Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-15 Xiaodong Xu, Michael R. Wisnom, Xiaoyang Sun, Tamas Rev, Stephen R. Hallett
Mode II fracture energy, GIIC, is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, ηG, for GIIC. A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined ηG can be successfully used to model the effect of TTC on delamination.
Inter-fibre failure of through-thickness reinforced laminates in combined transverse compression and shear load Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-13 Hao Cui, António R. Melro, Mehdi Yasaee
Extensive studies have been reported on the improvement of through-thickness reinforcement to inter-laminar performance of composite laminates; current understanding on the in-plane performance is relatively limited, although it is also concerned in industrial application. The influence of through-thickness reinforcement (Z-pinning) on the inter-fibre failure in compression of unidirectional laminates was investigated. Both unpinned and Z-pinned laminates were tested at four different off-axis angles, representing different combinations of transverse compression and in-plane shear stress. It was found that the stiffness of Z-pinned laminates decreased significantly in all off-axis angles. The failure strain and strength were reduced in shear dominated failure modes, while improved in the compression dominated failure modes by the presence of the Z-pins. A further investigation on the angle of failure plane was carried out and a comparison with analytical failure models is presented.
Nanodiamond decorated graphene oxide and the reinforcement to epoxy Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-11 Weixin Hou, Ya Gao, John Wang, Daniel John Blackwood, Serena Teo
Positively charged nanodiamond (ND) is used to decorate negatively charged graphene oxide (GO) to form a GO-ND hybrid nanomaterial by electrostatic force. Structural studies results showed that after the decoration, the aggregation of GO sheets is extensively hindered in both at the powder and dispersion states, with a clear reduction in the layer numbers in the latter. The mechanical properties of epoxy/GO, epoxy/ND and epoxy/GO-ND were investigated and compared. The results showed that the GO increased the ductility of epoxy, while the ND increased the rigidity. The best mechanical performance was found for the epoxy/GO-ND nanocomposites, at a GO:ND ratio of 1:5. The reinforcement mechanism of the nanophases was further illustrated by the fracture surface of SEM/optical images and TGA analysis. In addition, the anti-corrosion property of the thus developed epoxy nanocomposite coatings was revealed by electrochemical impedance spectroscopy (EIS), and the results demonstrated that the epoxy/GO-ND coatings exhibited better anti-corrosion property.
Exchangeable interfacial crosslinks towards mechanically robust elastomer/carbon nanotubes vitrimers Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-09 Min Qiu, Siwu Wu, Zhenghai Tang, Baochun Guo
Covalent bonds mediated interfaces are generally favorable for transferring interfacial stress and hence rationalizing the mechanical properties of the filled elastomeric composites. Aiming at reprocessable yet robust elastomeric composites, in this contribution, exchangeable interfacial crosslinks are introduced into the interfaces between epoxidized natural rubber (ENR) and multi-walled carbon nanotubes (MWCNTs). This is accomplished by functionalizing MWCNTs with carboxyl groups through diazo-coupling reaction and then incorporating the modified MWCNTs into diacid-cured ENR. Accordingly, covalent β-hydroxy ester bonds result in the interfaces between ENR and MWCNTs. The formation of covalent interfaces enables much uniform dispersion of MWCNTs and stronger interfacial adhesion. Comparing to the ENR filled with pristine MWCNTs, the modified composites exhibit much improved mechanical performance. Importantly, the exchangeable nature of interfacial β-hydroxy ester bonds has promoted effect on the reprocessibility of epoxy-MWCNTs vitrimers. Overall, we envision this interfacial strategy can provide an alternative avenue towards reprocessable yet robust elastomeric composites.
Strengthening carbon nanotube fibers with semi-crystallized polyvinyl alcohol and hot-stretching Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-09 Jialin Liu, Wenbin Gong, Yagang Yao, Qingwen Li, Jin Jiang, Yong Wang, Gengheng Zhou, Shuxuan Qu, Weibang Lu
The tensile mechanical properties of carbon nanotube (CNT) fiber, which is a one-dimensional assembly of ultra-strong CNTs, are still far short of our expectations. This is mainly due to their high porosity and relatively weak intertube load transfer efficiency. Previous studies have demonstrated that the fiber strength can be enhanced by the infiltration of polymer chains into the fiber. In this work, polyvinyl alcohol (PVA) was pre-infiltrated into loosely packed CNT ribbons, and the composite ribbons were then densified into the fiber form. This enabled a homogeneous dispersion of polymer chains within the CNT fibers. To enhance the mechanical properties of the CNT/PVA composite fibers, isothermal crystallization and ultrasonic treatments were implemented to increase the crystallization of PVA in the ribbon, and the composite fibers were hot-stretched to improve the alignment of both CNTs and PVA chains within the fibers. It was found that the tensile strength and modulus of the final composite fiber were 210% and 193.6% higher than those of the pristine CNT fiber. The structural evolution during these treatments and the mechanism of fiber strengthening were systematically investigated.
Enhancement of mechanical properties of buckypapers/polyethylene composites by microwave irradiation Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-08 Bo Qu, Dongxian Zhuo, Rui Wang, Lixin Wu, Xiuyan Cheng
Buckypapers (BPs) were generally laid up interleaved with polyethylene (PE) films to form BPs/PE composites after hot press. However, the mechanical properties of BPs/PE composites as-prepared were not good enough owing to poor impregnation and weak interfacial interactions between the matrix and carbon nanotube (CNT). In this paper, controlled microwave radiation treatment was applied on the BPs/PE composites. It is found that the microwave irradiation can effectively improve the tensile strength and stiffness of BPs/PE composites. Specifically, the tensile strength of BPs/PE composites increases from 20.9 MPa upto 34.1 MPa, 2.8 times that of pure PE, while the modulus increases from 880 MPa to 1778 MPa, 3.0 times that of pure PE. In addition, the structures (including fractured morphology, the interfacial composition between CNT and PE, structure of CNT and PE matrix, and crystallization) of BPs/PE nanocomposites with and without microwave irradiation were observed by SEM, FTIR, Raman, X-ray, and DSC, and then a mechanism of microwave irradiation to enhance the mechanical properties of BPs/PE composites was also proposed.
Electrically conductive GNP/epoxy composites for out-of-autoclave thermoset curing through Joule heating Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-07 Tian Xia, Desen Zeng, Zheling Li, Robert J. Young, Cristina Vallés, Ian A. Kinloch
The development of scalable Out-of-Autoclave (OoA) in-situ thermoset curing methods are required to overcome important drawbacks related to the autoclave-based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heating, emerges as a promising route to replace the conventional processing methods. In this work the electrical behaviour of both uncured and oven cured GNPs/epoxy composites with loadings of up to 10 wt.% were evaluated and electrical percolation thresholds were established for both. Above the critical loading found for oven cured materials (∼8.5 wt.%) the electrically conducting networks of GNPs formed in the matrix showed the ability to act as integrated nanoheaters when an electric current was passed through them, successfully curing the composites by Joule heating. Composites prepared by this OoA curing method (as an alternative to the traditional oven based one) at 10 wt.% loading of GNPs were also prepared and compared to the oven cured ones. They showed more compact composite structures, with less microvoids and a preferred orientation of the GNPs in the matrix relative to the oven cured material at identical loading, as revealed by electron microscopy and polarized Raman spectroscopy, respectively. This microstructure and anisotropy induced by the electrically-induced (i.e. OoA) cure led to GNPs/epoxy composites with superior electrical and mechanical properties (revealed by tensile testing). The well-distributed GNP nanoparticles acting as nanoheaters integrated in a thermosetting matrix, in combination with excellent mechanical and electrical performances achieved for the overall graphene/epoxy composites and the simplicity associated to the method, should open the door to novel industrial applications.
Transparent plywood as a load-bearing and luminescent biocomposite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-04 Qiliang Fu, Min Yan, Erik Jungstedt, Xuan Yang, Yuanyuan Li, Lars A. Berglund
Tailored glass fiber interphases via electrophoretic deposition of carbon nanotubes: Fiber and interphase characterization Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Qi An, Sandeep Tamrakar, John W. Gillespie, Andrew N. Rider, Erik T. Thostenson
Electrophoretic deposition (EPD) has been used to deposit carbon nanotubes (CNTs) onto glass fibers to strengthen the fiber/matrix interphase of glass/epoxy composites. CNTs were functionalized using an ultrasonicated-ozonolysis followed by polyethyleneimine (PEI) treatment, creating a stable, aqueous dispersion suitable for EPD. Single E-glass fiber filaments were successfully coated with the functionalized CNTs using EPD. Single fiber tensile and microdroplet debond tests were conducted to investigate the tensile properties of the CNT modified E-glass fibers and their interfacial structure and properties in an epoxy matrix, respectively. Weibull analysis of the fiber testing revealed no detrimental effects resulted from the CNT coating, with some evidence to suggest slightly improved strength. Microdroplet tests revealed changes in the fracture modes due to the application of the CNT coating. The interfacial shear-sliding shifted from the fiber/resin interface to the CNT/resin interphase for the CNT modified fibers. Higher effective interfacial shear strength corresponded to the results where fracture propagated deeper into the CNT-rich interphase layer, confirming the trends observed in previous model interphase studies.
Carbon nanotube-reinforced carbon fibre-epoxy composites manufactured by resin film infusion Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Mostafa Yourdkhani, Wenjiao Liu, Simon Baril-Gosselin, François Robitaille, Pascal Hubert
Effective dispersion of carbon nanotubes (CNTs) in the polymer matrix of fibre-reinforced composites is challenging due to the re-agglomeration and filtration of CNTs that occur during the processing of composite materials. In this study, resin film infusion (RFI) process is used for manufacturing composite laminates and investigating the degradation of CNT dispersion during high-temperature processing of a thermoset fibre-reinforced composite. Dispersion stability is investigated by studying the re-agglomeration of CNTs in the resin caused by variations in resin physiochemical properties. Filtration of CNTs by fibre tows is studied by investigating two layup strategies. The effect of CNT dispersion on the mechanical and electrical properties of composites is evaluated by performing compression-after-impact experiments and electrical conductivity measurements.
Synergetic effects of thin plies and aligned carbon nanotube interlaminar reinforcement in composite laminates Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-09 Estelle Kalfon-Cohen, Reed Kopp, Carolina Furtado, Xinchen Ni, Albertino Arteiro, Gregor Borstnar, Mark N. Mavrogordato, Ian Sinclair, S. Mark Spearing, Pedro P. Camanho, Brian L. Wardle
Thin-ply carbon fiber laminates have exhibited superior mechanical properties, including higher initiation and ultimate strength, when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and delamination-prone interlaminar regions. In this study, we report the first experimental realization of aligned carbon nanotube interlaminar reinforcement of thin-ply unidirectional prepreg-based carbon fiber laminates, in a hierarchical architecture termed ‘nanostitching’. We synthesize a baseline effective standard thickness laminate using multiple thin-plies of the same orientation to create a ply block, and we find an ∼15% improvement in the interlaminar shear strength via short beam shear (SBS) testing for thin-ply nanostitched samples when compared to the baseline. This demonstrates a synergetic strength effect of nanostitching (∼5% increase) and thin-ply lamination (∼10% increase). Synchrotron-based computed tomography of post mortem SBS specimens suggests a different damage trajectory and mode of damage accumulation in nanostitched thin-ply laminates, notably the complete suppression of delaminations in the nanostitched region. Finite element predictions of damage progression highlight the complementary nature of positive thin-ply and nanostitching effects that are consistent with an ∼15% improvement in Modes I and II interlaminar fracture toughness due to the aligned carbon nanotubes at the thin-ply interfaces.
Quantized prediction of coefficients of thermal expansion of 3-D CNT-Graphene junctioned carbon nanostructures Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Sangwook Sihn, Ajit K. Roy, Barry L. Farmer
A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective coefficients of thermal expansion (CTE) of a novel three-dimensional carbon nanostructure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically having different geometric parameters of pillar length and inter-pillar distance in the PGS. Periodic boundary conditions were applied to periodic unitcell geometries to yield consistent results. Parametric study shows that both pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness CTEs. The PGS with smaller inter-pillar distance and larger pillar length yields higher in-plane CTEs, while that with larger inter-pillar distance and smaller pillar length yields higher through-thickness CTE. The calculation yields negative through-thickness CTE at low temperatures ( T < 100 K) for all sets of PGSs, which is associated with the curvature at the junction.
Computer-aided design of three terminal (3T-) zig-zag SWCNT junctions and nanotube architectures Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-31 Sushan Nakarmi, Vinu U. Unnikrishnan, Vikas Varshney, Ajit K. Roy
Construction of topologically accurate models of nanotube junctions is essential for the determination of its thermal, mechanical and electronic properties. Most of the earlier nanotube junction models have been based on molecular dynamics (MD) simulations and heuristic methods which are either computationally expensive or impossible to model large 3D structures. CAD based approach that uses triangular meshes with remeshing strategies and have desired mesh optimization capability are found to be ideal to generate 3T-nanotube junctions with generic predefined orientation of nanotubes and accurate topological features. These 3T-junctions can be considered as building blocks and can be replicated in multiple directions to build complex nanotube architectures, which are shown via two examples for generating 2D and 3D microstructures by replication, translation, and rotation of a fused 3T-junction.
Nitrile butadiene rubber composites reinforced with reduced graphene oxide and carbon nanotubes show superior mechanical, electrical and icephobic properties Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-02 L. Valentini, S. Bittolo Bon, M. Hernández, M.A. Lopez-Manchado, N.M. Pugno
In this article, we examine the effects of two different nanostructured carbons when they are incorporated in a rubber matrix in terms of mechanical and electrical properties as well as the icephobic behaviour of the nanocomposites when swollen. Nitrile butadiene rubber composites reinforced with thermally reduced graphene oxide or multiwalled carbon nanotubes or both of them were prepared and characterized. At a particular hybrid filler loading, tensile and electrical tests showed a significant improvement of the composite. From the swelling studies, after the immersion, the nanocomposites experienced a reduction of the cross-link density that promotes weakening of ice adhesion, being this effect more evident for those samples prepared with hybrid fillers. In view of the composite formulations, that utilize commercially available elastomers and fillers, these findings would be applicable to the automotive and aviation sectors, where the demand for multifunctional rubbers is increasing.
Mechanical enhancement effect of the interlayer hybrid CNT film/carbon fiber/epoxy composite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-10 Tianshu Li, Min Li, Yizhuo Gu, Shaokai Wang, Qingwen Li, Zuoguang Zhang
Floating catalyst chemical vapor deposition carbon nanotube (CNT) film was intercalated into carbon fiber (CF) prepregs to fabricate hybrid composites. The effect of CNT film thickness was studied by using a 25 μm thick film and an ultrathin 2 μm film respectively. The results showed that the ultrathin CNT film interlayer had dramatically improved the compression strength of hybrid composite by 34% compared with CF/epoxy control composite owing to the altered failure modes. The damping ratio of ultrathin CNT film hybridized composite was substantially increased by two orders of magnitude, due to the energy dissipation of numerous nanoscale interconnections and interfaces. Moreover, the interlaminar properties and water resistance of the hybrid composites were all improved. Since a small amount of CNT film can significantly enhance the mechanical properties of CF/epoxy composite, this type of hybrid composite has potential application in multifunctional lightweight structures.
Simulating the effects of carbon nanotube continuity and interfacial bonding on composite strength and stiffness Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-14 Benjamin D. Jensen, Gregory M. Odegard, Jae-Woo Kim, Godfrey Sauti, Emilie J. Siochi, Kristopher E. Wise
Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations. The simulation results quantify the dependence of composite mechanical properties on the number of nanotube-matrix interfacial covalent bonds. Furthermore, the mechanical impact of interfacial bonding was decomposed to reveal its effect on the properties of the CNTs, the interfacial layer of matrix, and the bulk matrix. For the composites with continuous reinforcement, it was found that any degree of interfacial bonding has a negative impact on axial tensile strength and stiffness. This is due to disruption of the structure of the CNTs and interfacial matrix layer by the interfacial bonds. For the discontinuous composites, the modulus was maximized between 4% and 7% interfacial bonding and the strength continued to increase up to the highest levels of interfacial bonding studied. Areas of low stress and voids were observed in the simulated discontinuous composites at the ends of the tubes, from which fracture was observed to initiate. Experimental carbon nanotube yarn composites were fabricated and tested. The experimental results illustrate the knockdown factors that reduce composite mechanical properties relative to those of the tubes themselves.
How can we make carbon nanotube yarn stronger? Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-15 Yeonsu Jung, Young Shik Cho, Jae Won Lee, Jun Young Oh, Chong Rae Park
There has been remarkable progress with regard to the fabrication of yarns based on high-performance carbon nanotubes (CNTs). However, the theoretically predicted tensile strength of CNTs has yet to be realized in practical CNT yarns or CNT-reinforced composites. Having considered that there are few systematic guidelines for preparing high-strength CNT yarns, we attempted to revisit the-state-of-the-art progress in the theories and yarn formation processes of CNT yarns and then draw possible correlations between the intrinsic and extrinsic structural parameters of elementary CNTs, yarn formation processes and the tensile strength of the resulting CNT yarns. On the basis of these considerations and discussions of advanced technologies and theoretical approaches, possible routes to improve the strength of CNT yarns further are suggested.
Mechanical behavior of carbon nanotube yarns with stochastic microstructure obtained by stretching buckypaper Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-16 A. Sengab, R.C. Picu
The development of yarns composed primarily from carbon nanotubes (CNTs) has been pursued recently with the intent of transferring to the yarn the exceptional mechanical and transport properties of individual nanotubes. In this work we study the process of yarn formation by dry stretching buckypaper, and the mechanical behavior of the resulting yarns, function of the CNT length and of the state of the CNT assembly before stretching. The analysis is performed using a coarse grained, bead-spring representation for individual CNTs. It begins with a random buckypaper structure composed from CNTs of diameter 13.5 Å. This structure is stretched to form a yarn. This occurs once the stretch ratio becomes larger than a threshold which depends on the CNT length. At the threshold, adhesion stabilizes a highly aligned packing of CNT bundles. Packing defects and pores, reminiscent of the initial structure of the buckypaper, are incorporated in the yarn. The yarn is further tested in uniaxial tension. The defects have little effect on the mechanical behavior of the resulting yarns. However, the behavior depends sensitively on the degree of packing of the CNTs in the sub-bundles forming the yarn. Therefore, the initial structure of the buckypaper has little effect on the performance of the yarn. Increasing the CNT length increases the yarn flow stress and this is associated with the residual tortuosity of the CNTs in the yarn. Decreasing the temperature or increasing the strain rate lead to a small increase of the flow stress. These results have implications for yarn design, which are discussed in the article.
Advanced carbon fiber composite out-of-autoclave laminate manufacture via nanostructured out-of-oven conductive curing Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-02-26 Jeonyoon Lee, Xinchen Ni, Frederick Daso, Xianghui Xiao, Dale King, Jose Sánchez Gómez, Tamara Blanco Varela, Seth S. Kessler, Brian L. Wardle
Next-generation composite manufacturing processes are needed to overcome several limitations of conventional manufacturing processes (e.g., high energy consumption). Here we explore, via experiments and modeling, the characteristics of the newly developed out-of-oven (OoO) curing technique that cures a composite laminate via resistive heating of a carbon nanotube film. When compared to oven curing of an aerospace-grade out-of-autoclave (OoA) carbon fiber prepreg advanced composite laminate, the OoO curing reduces energy consumption by over two orders of magnitude (14 vs. 0.1 MJ). Thermophysical and mechanical tests including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), short beam shear (SBS), and ex-situ and in-situ double-edge notch tension (DENT) indicate that the physical and mechanical properties of OoO-cured laminates are equivalent to those of oven-cured (baseline) laminates. In addition to energy savings, the OoO curing process has the potential to reduce part-to-part variations through improved spatiotemporal temperature control.
Strong process-structure interaction in stoveable poly(urethane-urea) aligned carbon nanotube nanocomposites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-03 Jeffrey L. Gair, Robert H. Lambeth, Daniel P. Cole, Dale L. Lidston, Itai Y. Stein, Estelle Kalfon-Cohen, Alex J. Hsieh, Hugh A. Bruck, Mark L. Bundy, Brian L. Wardle
The exceptional static and dynamic physical properties of poly(urethane-urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a >3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications.
Multiscale modeling of carbon fiber/carbon nanotube/epoxy hybrid composites: Comparison of epoxy matrices Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-09 M.S. Radue, G.M. Odegard
This study addresses the multiscale modeling of hybrid composites composed of carbon fibers (CFs), carbon nanotubes (CNTs), and three different epoxy systems (di-, tri-, and tetra-functional resin epoxies). Molecular dynamics (MD) simulations are performed to predict the molecular-level interfacial and mechanical behavior of CNT embedded in epoxy. Micromechanics calculations are implemented to translate the molecular phenomena observed to predict the mechanical properties of CNT/epoxy composites with randomly oriented CNTs and CF/CNT/epoxy systems with aligned CFs and randomly oriented CNTs. The model is validated with experimental Young's modulus values for CNT/epoxy available in the literature. The results demonstrate that the tri- and tetra-functional resin epoxies demonstrate comparably high moduli over the di-functional resin for CNT concentrations up to 5 wt%. For higher CNT loadings, the tri-functional resin epoxy is predicted to outperform the other resins with respect to stiffness due to its strong interaction with CNTs and high bulk stiffness.
Grafting carbon nanotubes onto carbon fibres doubles their effective strength and the toughness of the composite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-14 Luca Lavagna, Daniele Massella, Maria F. Pantano, Federico Bosia, Nicola M. Pugno, Matteo Pavese
Bioinspiration can lead to exceptional mechanical properties in a number of biological materials as a result of their internal structure. In particular, the hierarchical arrangement of nano-to macro-components can bring to complex energy dissipation mechanisms and unprecedented resistance to crack growth. In this work, we propose to exploit this approach, combining in a multiscale composite structure carbon nanotubes with conventional carbon fibre reinforcements in a polyvinyl butyral matrix. We show that grafting the nanotubes onto the carbon microfibres improves their interface properties with the matrix considerably, effectively doubling their apparent strength. At the same time, the addition of nanotubes to microfibre reinforcements helps to improve the composite toughness, reaching more than twice the value for the conventional, non-hierarchically reinforced composite. Numerical simulations and fracture mechanics considerations are also provided to interpret the results.
Mesoscopic modeling of the uniaxial compression and recovery of vertically aligned carbon nanotube forests Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-14 Bernard K. Wittmaack, Alexey N. Volkov, Leonid V. Zhigilei
Vertically aligned carbon nanotube (VACNT) arrays or “forests” represent a promising class of mechanically strong and resilient lightweight materials, capable of supporting large reversible deformation and absorbing mechanical energy. The mechanical response of VACNT forests to uniaxial compression is defined by various factors, including the material microstructure, its density, height, rate of deformation, and the nature of interaction between carbon nanotubes (CNTs) and the compressing indenter. In this paper, we use a coarse-grained mesoscopic model to simulate the uniaxial compression of VACNT samples with different densities and microstructures (bundle size distribution and degree of nanotube alignment) to obtain a clear microscopic picture of the structural changes in networks of interconnected CNT bundles undergoing mechanical deformation. The key factors responsible for the coordinated buckling of CNTs, reversible and irreversible modes of deformation in VACNT arrays undergoing uniaxial compression, as well as hysteresis behavior in VACNT arrays subjected to five loading–unloading cycles are investigated in the simulations. The simulation results reveal the important role of the collective buckling of CNTs across bundle cross-sections as well as a complex deformation behavior of VACNT arrays defined by an interplay of different modes of bundle deformation. The loading rate and the CNT attachment to the indenter are found to have a strong effect on the deformation mechanisms and the overall mechanical behavior of VACNT forests. A good agreement with experimental data from in situ mechanical tests is observed for the general trends and magnitudes of loss coefficients predicted in the simulations. The forest morphology can strongly alter the mechanical behavior of VACNT arrays with nominally the same general characteristics, such as CNT radius, length, and material density, thus suggesting the opportunity for substantial enhancement of the mechanical properties through the microstructure modification.
Multiscale modeling of photomechanical behavior of photo-responsive nanocomposite with carbon nanotubes Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-27 Junghwan Moon, Hyunseong Shin, Kyungmin Baek, Joonmyung Choi, Maenghyo Cho
We propose a scale-bridging methodology to link the microscopic photoreaction of an azobenzene-containing liquid crystalline polymer (LCP) and the macroscopic interfacial and elastic properties of carbon nanotube (CNT)-reinforced photo-responsive nanocomposites. The photo-isomerization of the azobenzene moieties is described by implementing a photo-switching potential that represents the light-excited energy transition path. The relevant time evolution of the molecular shape and the concurrent changes in the interfacial morphology are observed using molecular dynamics (MD) simulations. Finally, the effective elastic properties of the photo-responsive polymer (PRP) nanocomposite with respect to the isomerization ratio are numerically derived using the micromechanics-based homogenization method. It is verified that the size of the CNT and the photo-deformation of the azobenzene molecules influence the intermolecular interactions and the nematic phase of the LCP at the interfacial region. The continuum-scale finite element (FE) model, which reflects the microscopic information, clearly predicts the reinforcing effect of the CNT filler on the elastic properties of the composite and their variation under photo-actuation. We expect our results to shed light on designing the photomechanical energy conversion efficiency of nano-sized soft actuators composed of CNT-reinforced composites.
Machine learning electron density in sulfur crosslinked carbon nanotubes Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-03-29 John M. Alred, Ksenia V. Bets, Yu Xie, Boris I. Yakobson
Mechanical strengthening of composite materials that include carbon nanotubes (CNT) requires strong inter-bonding to achieve significant CNT-CNT or CNT-matrix load transfer. The same principle is applicable to the improvement of CNT bundles and calls for covalent crosslinks between individual tubes. In this work, sulfur crosslinks are studied using a combination of density functional theory (DFT) and classical molecular dynamics (MD). Atomic chains of at least two sulfur atoms or more are shown to be stable between both zigzag and armchair CNTs. All types of crosslinked CNTs exhibit significantly improved load transfer. Moreover, sulfur crosslinks show evidence of a cooperative self-healing mechanism allowing for links to rebond once broken leading to sustained load transfer under shear loading. Additionally, a general approach for utilizing machine learning for assessing the ground state electron density is developed and applied to these sulfur crosslinked CNTs.
Enhanced energy storage performance of ferroelectric polymer nanocomposites at relatively low electric fields induced by surface modified BaTiO3 nanofibers Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-06-02 Zeyu Li, Feihua Liu, Guang Yang, He Li, Lijie Dong, Chuanxi Xiong, Qing Wang
Polymer nanocomposite dielectrics with high energy densities have shown great potential in electrical energy storage applications. However, these high energy densities are normally achieved at ultrahigh applied electric fields (≥400 MV/m), which is inconvenient for certain applications such as aerospace power systems and microelectronics. In this study, uniform BaTiO3 nanofibers (BT nfs) with a large aspect ratio were prepared via the electrospinning method, surface modified by poly(vinyl pyrrolidone) (PVP) and utilized as the fillers in the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanocomposites. It is found that the nanocomposite with 3 vol% BT nfs possesses a much enhanced discharged energy density of 8.55 J/cm3 at an applied electric field of 300 MV/m, which is 43% higher than that of the neat polymer matrix (i.e. 5.98 J/cm3) and more than four times that of the commercial biaxial oriented polypropylene dielectric (2 J/cm3 at over 600 MV/m). Comparative studies have been performed on the corresponding nanocomposites with BT nanoparticle fillers and pristine BT nfs. The improved energy storage performance is ascribed to the synergetic effects of surface modification and large aspect ratio of BT nfs. Our research provides a facile and effective approach to high-performance electrical energy storage materials which work efficiently at relatively low operating voltages.
Imidazolium-grafted graphene oxide via free radical polymerization: An efficient and simple method for an interpenetrating polymer network as electrolyte membrane Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-31 Amina Ouadah, Tianwei Luo, Jing Wang, Shuitao Gao, Xing Wang, Xin Zhang, Zhou Fang, Zeyu Wu, Jie Wang, Changjin Zhu
Surface modification of carbon fibers by microwave etching for epoxy resin composite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-31 Jian-Min Yuan, Ze-Fu Fan, Qing-Cheng Yang, Wei Li, Zhen-Jun Wu
Microwave irradiation was applied to modify the carbon fibers immersed in water. The surface chemical composition and morphology of treated carbon fibers were investigated in detail. It showed that great numbers of oxygen-containing groups were introduced in treated carbon fiber surfaces and nitrogen heterocyclic rings of carbon fiber bulk exposed for the exfoliation of surface layers. The surface roughness of carbon fibers was enlarged by oxidative etching of microplasma excited by microwave irradiation, and some nano humps were formed on carbon fiber surfaces. Although the tensile strength of treated carbon fibers were slightly deteriorated, the interfacial shear strength of treated carbon fibers/epoxy resin composite, as compared with that of untreated carbon fibers/epoxy resin composite, was significantly enhanced. The modification mechanism is that the microplasma and the exfoliation of monolayer graphene oxide sheets lead to the variations of chemical structure and physical morphology in carbon fiber surfaces.
Interfacially reinforced unsaturated polyester carbon fiber composites with a vinyl ester-carbon nanotubes sizing agent Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-31 Zijian Wu, Hongyu Cui, Lei Chen, Dawei Jiang, Ling Weng, Yingyi Ma, Xuejiao Li, Xiaohong Zhang, Hu Liu, Ning Wang, Jiaoxia Zhang, Yong Ma, Mingyan Zhang, Yudong Huang, Zhanhu Guo
A amino-functionalized carbon nanotubes (CNTs)-containing sizing agent was prepared for improving the interface bonding and impact toughness of carbon fibers (CFs) reinforced unsaturated polyester (UP) composites. More reactive groups and better interfacial compatibility with UP make vinyl resin M7270 a more suitable polymer for preparing sizing agent for CF/UP composites when compared to epoxy, MR13006 and R806. The surface characteristics of CFs and the interfacial properties of the composites before and after surface modification were investigated. The observed uniformly dispersed CNTs-containing sizing agent on the CF surface obviously increased the surface roughness. The amount of polar functional groups and the wettability of CFs were significantly enhanced after the coating treatment. The interlaminar shear strength (ILSS) and impact toughness were enhanced by 32.3 and 55.2%, respectively. The sizing agent effectively enhanced the interfacial adhesion by improving the surface energy, and increasing chemical bonding and mechanical interlocking.
Effect of PA6T on morphology and electrical conductivity in PA66/PA6T/PPE/multiwalled carbon nanotube nanocomposites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-30 Minho Lee, Kwonsang Son, Jeongyup Kim, Donghyeon Kim, Byong Hun Min, Jeong Ho Kim
Nanocomposites made of blends of polyamide (PA66), polyphthalamide (PA6T), and poly(2,6-dimethyl-1,4-phenylene ether) (PPE) with multi-walled carbon nanotubes (CNTs) were investigated. At 1 wt% CNT loading, the electrical conductivities of PA66/PA6T/PPE/CNT nanocomposites were around four orders of magnitude larger than those of PA66/PPE/CNT nanocomposites without PA6T. Line mapping images and spot spectrum results from transmission electron microscopy/energy dispersive spectroscopy analysis showed that the continuous phase contained PA66 and PA6T with dispersed PPE domains. Phase inversion was observed as the CNT content of PA6T/PPE/CNT increased. Depending on the polymer composition, alignment of some of CNTs at the interface was observed. Using the wetting coefficient analysis and the Hansen solubility parameter, the morphologies of the nanocomposites and the resulting electrical conductivities were found to be affected by the compatibilizing effect of PA6T on PA66 and PPE as well as the higher affinity of CNTs for PA6T than for PPE or PA66. CNTs were observed to help maintain the integrity of the PA66/PA6T continuous phase by dynamic mechanical analysis.
Flexible, conductive, and highly pressure-sensitive graphene-polyimide foam for pressure sensor application Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-30 Jiayi Yang, Yusheng Ye, Xiaoping Li, Xiaozhou Lü, Renjie Chen
Three-dimensional porous graphene foams have received increasing attention in the fields of sensors, flexible conductors, and energy storage. Mechanical stability, flexibility, and electrical conductivity are prerequisites for materials used in these fields. In this paper, novel polyimide-based graphene foam was prepared by dip-coating a polyimide foam template followed by chemical reduction and thermal reduction. The prepared foam displayed excellent mechanical stability and flexibility (elastic modulus: ∼5 kPa). The synergistic effects of chemical and thermal reduction led to a foam with high electrical conductivity of ∼0.4 S m−1. By controlling the dip-coating times, the foam achieved a high pressure sensitivity of 0.36 kPa−1. Experiments show that the prepared foam can be used as effective pressure sensor to measure heartbeat, joint activity, and airflow.
A three-dimensional unit cell model with controllable crimped structure for investigating finite strain response of collagen fiber reinforced biological composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-30 Li Liu, Dean Hu, Xu Han
Composite materials reinforced by crimped fibers, such as collagen fibers, have a widely application in the advanced structures. Therefore, an effective and achievable model is significant for explicitly describing the geometry of the crimped fibers and evaluating their mechanical behaviors. Aiming at this purpose, a three-dimensional (3D) unit cell model (UCM) is developed based on the microstructure of the collagen fibers, in which a controllable modified sinusoidal waviness fiber is explicitly embedded into the soft matrix, and an effective periodic boundary condition is applied on the proposed 3D UCM by using the multi-points constraint equations. The accuracy and validity of the proposed model are verified by comparing with the existing experimental results. For investigating the influence of the geometric parameters on the mechanical responses of the crimped fiber reinforced composites, several numerical UCMs with different geometric parameters are presented. The obtained results reveal that the parameters of crimp amplitude H and waviness χ of the fibers mainly contribute to the flexibility of the materials. The parameter ω for characterizing the roughness of the fibers is associated with the size and position of largest stress region. Moreover, the fiber radius R plays an important role in determining the bearing capacity of the materials and an excellent mechanical property, e.g., not only withstands the large initial tensile load but also has a special ability to guarantee the flexibility of the materials, may be achieved by controlling the number of the fibers with big and small radii.
Largely enhanced fracture toughness of the PP/EPDM blends induced by adding carbon nanofibers Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-30 De-xiang Sun, Chao-jin Yang, Xiao-dong Qi, Jing-hui Yang, Yong Wang
In this work, a small quantity of carbon nanofibers (CNFs) were incorporated into polypropylene/ethylene-propylene-diene terpolymer (PP/EPDM) blends. The effects of CNF content on the processing flowability, the microstructure of PP matrix and the morphology of elastomer particles were investigated. The results showed that the processing flowability of the material was not apparently influenced. The straight CNFs selectively located in the PP matrix and exhibited oriented dispersion along the flow direction of melt during the injection molding processing. CNFs exhibited nucleation effect on crystallization of PP. Homogeneous EPDM particles with smaller particle diameters were obtained in the blend composites. Mechanical properties measurements showed that the largely enhanced fracture toughness was achieved for the blend composites and the brittle-ductile transition was induced at lower EPDM content. Specifically, incorporating only 0.2 wt% CNFs into the PP/EPDM (85/15), the impact strength was enhanced about 246%. Further results showed that for the blend which exhibited brittle-fracture feature, the brittle-ductile transition could also be induced with increasing CNF content. The toughening mechanisms were then proposed.
Effect of tunable styrene content on achieving high-performance poly(styrene-b-ethylene-ran-butylene-b-styrene)/graphene oxide nanocomposites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-28 Jianfeng Wang, Xiuxiu Jin, Xiaomeng Zhang, Hong Wu, Shaoyun Guo
In this paper, two poly(styrene-b-ethylene-ran-butylene-b-styrene) (SEBS) with different styrene segment content were adopted to explore the relationship between varying π-π stacking interaction and the mechanical performance of polymer composites. The results showed that the high styrene content on SEBS (SEBS-30, 30 wt% styrene segment) endows SEBS a stronger π-π stacking interaction with GO and a better dispersion of GO in the matrix than that in SEBS with low styrene content (SEBS-12, 12 wt% styrene segment), resulting in a high efficiency on enhancing the performance of SEBS. By adding 0.5 wt% GO, the tensile strength and modulus of SEBS-30 was increased by 44% and 64%, respectively, while that of SEBS-12 was increased by 24% and 39%. Furthermore, the GO also exhibited the ability to toughen SEBS via forming microcrack and GO-induced fibrillation of SEBS during the fracture process. The elongation at break and fracture toughness of SEBS-30 was increased by 10% and 64%, respectively. This study gives us a deep insight into the influence of varying π-π stacking interaction between graphene oxide (GO) and polymer on achieving high-performance polymer nanocomposites.
One-pot method to reduce and functionalize graphene oxide via vulcanization accelerator for robust elastomer composites with high thermal conductivity Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-29 Huanhuan Dong, Zhixin Jia, Yongjun Chen, Yuanfang Luo, Bangchao Zhong, Demin Jia
A high-efficiency and rapid one-step approach was developed to simultaneously reduce and functionalize graphene oxide (GO) with vulcanization accelerator 2-mercaptobenzothiazole (M) under mild conditions (2 h, 80 °C, neutral and non-toxic environmental condition). The reduced GO chemically grafted with ca. 25 wt% M (M-G) not only eliminated the harmful blooming of vulcanization accelerator but also reduced the irreversible graphene agglomerates and improved the compatibility between graphene and elastomer, aiding the uniform dispersion of M-G nanosheets in elastomer matrix and enhancing the graphene-elastomer interfacial interaction. As a result, elastomer composites with M-G nanosheets showed much better combination of high tensile strength, large extensibility and superior thermal conductivity than elastomer composites with hydrazine hydrate reduced GO containing equal filler and vulcanization accelerator contents. The approach of using rubber additives to reduce and functionalize GO may provide some new insights in the green production of organically modified graphene and in the designing of high performance rubber/graphene materials.
Highly thermal conductive and electrically insulating polymer composites based on polydopamine-coated copper nanowire Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-29 Hao Yuan, Yang Wang, Ting Li, Piming Ma, Shengwen Zhang, Mingliang Du, Mingqing Chen, Weifu Dong, Weihua Ming
Fabrication of a bulk superhydrophobic conductive material by mechanical abrasion Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-25 Zhiming Cai, Lie Shen, Xiaojing Wang, Qipeng Guo
A Ketjen black (KB)-vapour-grown carbon fibre (VGCF)/polypropylene (PP) bulk superhydrophobic conductive material was prepared by processing the mixture with a range of roughnesses of abrasive paper. The difference in abrasion resistance between fillers and resin induces surface roughness during abrasion. SEM images showed hierarchically structured roughness that consists of heaves with fillers. The influence of the loading and ratio of the fillers was investigated. When the loading of the fillers was 33.3 wt% and the ratio of KB to VGCF was 4:1, the surface showed a static water contact angle of approximately 167.5°, a sliding angle below 1°, and a volume resistivity of approximately 0.8 Ω cm. The superhydrophobicity of the material was stable over a wide range of pH, temperature and appropriate mechanical abrasion. The bulk material is environmentally friendly, easy to scale up for large-scale applications and may be useful for anti-icing applications or self-cleaning.
Synthesis of novel multilayer composite microcapsules and their application in self-lubricating polymer composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-24 Haiyan Li, Yingjie Ma, Zhike Li, Yexiang Cui, Huaiyuan Wang
Novel lubricant oil-loaded multilayer composite microcapsules with poly(urea-formaldehyde) (PUF) shells assembled with polydopamine-functionalized oxidized carbon nanotubes (CNTs-o-PDA) are fabricated. Results indicate that the PUF microcapsules show spherical shape structure with a mean diameter of 110 μm and an encapsulation capacity of 83.5%. CNTs are successfully assembled on the surface of lubricant oil-containing PUF microcapsules (LPMs). Thermal stability tests reveal the initial decomposition temperature of microcapsules elevated by 75 °C. Furthermore, the microcapsules are embedded into epoxy to prepare self-lubricating composites. The coefficient friction and wear rate of self-lubricating composites incorporating 20 wt% CNTs-o-PDA assembled LPMs are 33.79% and 74.28% lower than that of composites incorporating LPMs, and which are 64.07% and 99.54% lower than that of the pure epoxy resin, respectively. Further studies confirm that the interface bonding strength between epoxy and microcapsules is effectively improved by the introduction of CNTs-o-PDA on the surface of PUF microcapsules. The synergistic effect between microcapsules containing lubricant oil and CNT layer played an important role in improving the tribological properties of polymer composites.
Facile method to functionalize graphene oxide nanoribbons and its application to Poly(p-phenylene benzobisoxazole) composite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-23 Mingqiang Wang, Chunyan Wang, Yuanjun Song, Chunhua Zhang, Lu Shao, Zaixing Jiang, Yudong Huang
Graphene oxide nanoribbons (GONRs), as a new member of carbon family, attracted extensive attention in industry and science field. It has considered to be as a promising nanomaterial for applications in the field of materials science, energy storage and optics science due to its extraordinary mechanical, electrical and thermal properties. Hence, in this study, we carried out a facile and efficient strategy for preparing poly (phenylene benzobisoxazole) (PBO)/GONRs(PGR) composite fibers via one-pot in situ polycondensation method for enhancement in mechanical and thermal properties. The GONRs sheets in this work were obtained by unwrapping multi-walled carbon nanotubes (MWCNTs) side walls, and then directly reacted with PBO monomer 4,6-diaminoresorcinol(DAR) and covalently grafted on PBO molecular chains. The structure and morphology of GONRs and modified GONRs were well demonstrated by the FT-IR, XPS and TEM analysis for confirming the formation of chemical bond between GONRs and PBO molecular chains. The mechanical and thermal properties of PGR composite fibers were also investigated. It was found that the performance of composite fibers about 32.1% improvement in tensile modulus, 24.2% in tensile strength and 10.5% thermal stability, respectively.
Fabrication and mechanical properties of CFRP composite three-dimensional double-arrow-head auxetic structures Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-22 Xin-Tao Wang, Bing Wang, Zhi-Hui Wen, Li Ma
In recent years, 3D structures with negative Poisson's ratio (auxetic) have attracted great interest. Many polymer and metal 3D auxetic structures have been manufactured using additive manufacturing technology, however composite 3D auxetic structures are rarely reported. Auxetic structures are normally of low stiffness which causes limitations on the structural applications of them. The specific stiffness and strength of auxetic structures can be significantly improved by making them from high-performance fibre reinforced polymer (FRP) composites. Consequently, research of composite 3D auxetic structures made from FRP should be conducted. This paper presents the composite 3D double-arrow-head (DAH) auxetic structure made from carbon fibre reinforced polymer (CFRP) using an assembly method. Experimental, finite element and theoretical methods are adopted to study the mechanical properties of the composite 3D DAH auxetic structures. Results show that the Poisson's ratios and effective compression moduli of the composite 3D DAH auxetic structures vary depending on the compression strain amplitude, and the structures become more auxetic and stiffer with the increase of the compression strain. The specific stiffness of the composite 3D DAH structure is much higher than that of the metal structure. In addition, the dependences of the structure's Poisson's ratio and effective compression modulus on the geometry parameters have also been given. Making auxetic structures from high-performance FRP composites can significantly improve their mechanical properties which will enable them to have a much wider variety of applications.
Mechanical properties of polypropylene by diversely compatibilizing with titanate whiskers in composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-21 Xuechun Wang, Renfeng Song, Yinjie Chen, Yunhui Zhao, Kongying Zhu, Xiaoyan Yuan
Isotactic polypropylene (PP)/titanate whisker composites were tailored by two component blends, in which PP and the titanate fillers were processed with maleic anhydride grafted polypropylene (PP-g-MAH) and maleic anhydride grafted polyethylene (PE-g-MAH) as compatibilizing agents, respectively. The whiskers modified with silica and 3-aminopropyl triethoxysilane ensured the hybrid interfacial conceivement, and the usages of the diverse compatibilizers were intended for toughening effect and balanced mechanical properties of PP. Positively compatible PP-g-MAH and anti-compatible PE-g-MAH endowed the composites of PP/titanate whiskers with remarkable rise in notch impact strength of 7.4 ± 0.1 kJ/m2, which was significantly higher than 3.1 ± 0.4 kJ/m2 for PP with trivial deterioration to both tensile and flexural strengths. Differential scanning calorimetry results demonstrated the presence of β-form crystals in the composite, favoring the extra improvement of impact toughness. Variations of glass transition temperature and storage energy detected by dynamic mechanical analysis also revealed both of the compatibilizing agents worked in the composites for reinforcement. With the greatly improved tenacity as well balanced tensile and flexural properties in the composite, PP could find its potentials as impact plastic materials.
Effect of hierarchical structure on electrical properties and percolation behavior of multiscale composites modified by carbon nanotube coating Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-21 Jie Zhang, Alexei A. Bokov, Shang-Lin Gao, Nan Zhang, Jian Zhuang, Wei Ren, Zuo-Guang Ye
The hierarchical composites integrated by micro-/nano-fillers have been considered to be the multifunctional materials of the next generation. However, the effects of the hierarchical architecture on the electrical properties of composites remains poorly understood. Here, the fabrication of polymer-based multiscale composites with hollow glass fibers coated by carbon nanotubes (CNTs) and the investigation of their morphology, conductivity and dielectric properties are reported. Owing to CNTs introduced into the interfaces, various electrical parameters of the composites are obviously improved. The composite exhibits a stronger anisotropy than that of carbon fiber or CNTs filled composites and an ultralow percolation threshold. These unique behaviors are shown to be related to the hierarchical morphology giving rise to the existence of two percolation levels with different thresholds: a local threshold in the nanoscale CNT networks at the fiber-polymer interfaces and a global threshold in 3D network formed by the fibers. Furthermore, we find and explain some behaviors uncharacteristic of binary composites and the other hierarchical composites. This work provides a deeper understanding of the relationship between the structure and properties of multiscale composites and other complex percolating systems, potentially opening up new ways for designing novel materials.
Self-healing, recoverable epoxy elastomers and their composites with desirable thermal conductivities by incorporating BN fillers via in-situ polymerization Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-21 Xutong Yang, Yongqiang Guo, Xian Luo, Nan Zheng, Tengbo Ma, Jiaojun Tan, Chunmei Li, Qiuyu Zhang, Junwei Gu
Thiol-epoxy elastomers were firstly prepared by thiol-epoxide nucleophilic ring-opening reaction, and the micron boron nitride (mBN) fillers were then introduced into the above system via in-situ polymerization, finally to prepare the highly thermally conductive, self-healing and recoverable mBN/thiol-epoxy elastomer composites by hot-pressing method. Results revealed that the thiol-epoxide reaction was highly efficient and stable. The obtained mBN/thiol-epoxy elastomer composite with 60 wt% mBN fillers presented the optimal thermal conductivity (λ of 1.058 W/mK), excellent self-healing effect & efficiency which is achieved via transesterification reaction (Tensile strength after self-healing could maintain at more than 85% compared to that of original composites), wonderful recoverable performance (Tensile strength after post forming could maintain over 70% compared to that of original composites) and good thermal stability (Theat-resistance index, THRI of 149.9 °C). And the improvement in λ value of the mBN/thiol-epoxy elastomer composites was beneficial to the promotion of the self-healing systems relying on thermal response.
A novel stiffener skeleton strategy in catalytic carbonization system with enhanced carbon layer structure and improved fire retardancy Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-22 Dongsheng Wang, Xin Wen, Xuecheng Chen, Yunhui Li, Ewa Mijowska, Tao Tang
Catalyzing carbonization of polymer itself to form a protective carbonaceous layer has been proven to be an effective way to improve polymer's flame retardancy, but there is still a great challenge to achieve synchronous enhancement in traditional test standards (such as LOI and UL-94 testing). In this study, a stiffener skeleton strategy combined with catalyzing carbonization was proposed to improve the flame retardancy of polycarbonate (PC). The synergistic effect of nanosized carbon black (CB)/Ni2O3 on carbon yield and combustion properties of PC were investigated. An improvement with 31.4% in LOI, V0 in UL-94, and 50% reduction for PHRR in cone calorimeter test was achieved. According to char morphology and structure analysis, the flame retardancy mechanism was attributed to the enhanced barrier effect of carbon layer with interconnected structure and self-supporting capacity, which was promoted by the formation of carbon skeleton framework from PC and the catalytic carbonization from combined catalysts.
Enhancement in thermal conductivity of polymer composites using aligned diamonds coated with superparamagnetic magnetite Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-22 Mingqi Sun, Bing Dai, Kang Liu, Kaili Yao, Jiwen Zhao, Zhijun Lyu, Peng Wang, Yujie Ding, Lei Yang, Jiecai Han, Jiaqi Zhu
We report magnetic alignment of single-crystalline microdiamonds with aid of superparamagnetic magnetite in polymeric composites and their material properties. The silicone composite containing aligned microdiamonds shows interesting properties in alignment direction, including enhancement of thermal conductivity, 250% higher than that of randomly dispersed counterpart at a low loading of 5.1 vol%. Composites with aligned diamond exhibited enhanced thermal conductivity and electrical insulation compared with matrix, and are attractive for application as thermal interface materials in the semiconductor industry, though the introduction of magnetite had part of negative effect on electrical resistivity of composites. A two-level model that accounts first-order interaction between particles to calculate effective thermal conductivity of composites with aligned microdiamonds, is found to fit accurately absolute value and tendency of thermal conductivity for composites with aligned particles. Utilizing the modeling procedure, the volume fraction of microdiamonds within chains is 0.3, which is smaller than 0.698 predicted for ideal body-centered-tetragonal arrangement of particles. This suggested that thermal conductivity of composites can be enhanced further by improving microstructures within particle chains.
Anti-icing and de-icing coatings based Joule's heating of graphene nanoplatelets Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-19 O. Redondo, S.G. Prolongo, M. Campo, C. Sbarufatti, M. Giglio
Epoxy coatings doped with graphene nanoplatelets (GNP) with average thickness close to 200 μm have been manufactured on glass fibre laminate substrate. Their electrical conductivity was close to 0.001–0.01 S/m because the GNP percentages added (8–12 wt% GNP) were higher than the electrical percolation threshold of this GNP/epoxy system. The electrical current increases exponentially with the applied voltage due to the self-heating of the samples. Therefore, these materials don't follow the Ohm's law. Interestingly, the electrical resistance remains constant, or even decreases, at cryogenic temperatures. Self-heating of GNP/epoxy coatings due to Joule's effect was also studied, analysing the effect of the applied voltage. The coating doped with the highest GNP content presented more efficient heating due to its higher electrical conductivity and therefore higher transported electrical current. The application of a relatively high voltage, 750–800 V, induced the self-heating of materials, which was used for anti-icing and de-icing applications. Different thermoelectrical tests at low temperatures, between −10 and −30 °C, have been designed and carried out, confirming the high efficiency of these materials as an anti-icing and de-icing system (ADIS) which required low electrical power, close to 2.5 W, showing a short time to melt the ice and high reproducibility.
Failure load prediction for fiber-reinforced composites based on acoustic emission Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-20 Markus G.R. Sause, Stefan Schmitt, Sinan Kalafat
In the design and quality control of fiber-reinforced structures, testing on coupon level and structure level are frequently carried out. In order to accept or reject a final product or material charge, means of quality control are carried out. In safety relevant structures, this is often based on holding a certain proof load. Acoustic emission is already used for the monitoring during proof load testing, but is only used for simple accept/reject diagnosis. For the accepted components typically no assessment is made for the expected residual capacity. We propose an acoustic emission based approach able to perform prediction of the ultimate strength values and to evaluate the materials present stress exposure while being tested. We base our approach on accepted acoustic emission measures, such as the Felicity ratio or the Shelby ratio to assess the structural integrity. Using a combination of an artificial neural network to predict the materials present stress exposure and a simple linear extrapolation we are able to predict the failure strength within the margin of prediction error for all test cases studied. The approach is benchmarked for three types of specimens, systematically changing test volume and load condition. We used tensile tests on fiber-reinforced thermoplastic tape samples, classical tensile test samples and bearing strength samples, all made from the same material.
Aging resistant TiO2/silicone rubber composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-20 Monika Bleszynski, Maciej Kumosa
We have recently shown [1,2] that one component room temperature vulcanized (RTV-1) silicone rubbers (SIR) based on polydimethylsiloxane (PDMS) can be rapidly degraded by low voltage (LV) energized aqueous salt solutions by previously unreported aging mechanisms related to the formation of hypochlorous acid in high voltage (HV) transmission line applications. In this study, we are showing how to improve the resistance of the rubbers to extreme environmental aging by embedding TiO2 micro-particles. Molecular dynamics (MD) simulations were conducted to determine the combined effect of TiO2 and different concentrations of hydrophobic PDMS methyl groups on surface hydrophobicity of a TiO2/PDMS composite. In addition, the effects of both TiO2 and silica on the diffusivities of LV aqueous salt components in the PDMS were predicted and related to unique interfacial interactions between the particles and the methyl groups of the PDMS. Rutile TiO2 reoriented methyl groups away from the particles reducing the diffusivities of water and hypochlorous acid. This effect shielded the PDMS network against environmental chain scissions. On the other hand, silica attracted the groups accelerating acid and water migrations and thus enhancing damage to the network. In the experimental part, TiO2/RTV was subjected independently to hypochlorous acid and electrolyzed LV aqueous salt. As expected, TiO2 greatly increased the contact angle, reduced the surface energy and improved the hydrophobicity of the composite, mitigating the negative effect of the reduced concentrations of methyl groups. As a result, aging damage to the rubber was dramatically reduced by about 50% in highly oxidative environments.
Core-shell nanoparticles toughened polylactide with excellent transparency and stiffness-toughness balance Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-19 Yuan Chen, Mingwang Pan, Yue Li, Jia-Zhuang Xu, Gan-Ji Zhong, Xu Ji, Zheng Yan, Zhong-Ming Li
Compatibilization of multicomponent composites through a transitioning phase: Interfacial tensions considerations Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-19 J.Justin Koh, Xiwen Zhang, Junhua Kong, Chaobin He
A novel interfacial compatibilization technique for incompatible polymer blends or composites is proposed, in which a transitioning layer was introduced between the matrix and the dispersed phase of the otherwise incompatible components. The transitioning phase should have good interactions with both the components, resulting in lower interfacial energy between the phases. Theoretically, it is hypothesized that if the sum of the interfacial tension between the transitioning phase and both the components of the composite is smaller than the interfacial tension between the two components, the encapsulation of the dispersed phase by the transitioning phase is spontaneous, which will lead to better interphase interfacial interactions. Since this compatibilizing technique relies purely on judicial selection of a polymer with suitable surface energy as the transitioning layer, no tedious chemical synthetic processes are required. To illustrate the proposed technique, incompatible Poly(lactic acid)/Thermoplastic Starch (PLA/TPS) blend is compatibilized with Poly(butylene succinate) (PBS) as the transitioning layer in this paper. With PBS encapsulating the dispersed TPS phase, PLA/PBS/TPS 60/10/30 wt% demonstrate a better mechanical synergy, with significant improvement in strength, ductility and toughness as compared to PLA/TPS 70/30 wt%. This technique can also be applied to design other multicomponent blends or composites.
A bioinspired multilayer assembled microcrack architecture nanocomposites for highly sensitive strain sensing Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-19 Zhenming Chen, Xuehui Liu, Shuman Wang, Xinxing Zhang, Hongsheng Luo
Despite the wide applications of strain sensor in wearable devices and electronic skins, the poor flexibility, low sensitivity and repeatability, as well as the utilization of noxious agents dramatically restrict its large-scale application. Herein, a simple and efficient strategy is demonstrated to fabricate flexible, ultrahigh sensitive and reproducible strain-sensing platforms via an eco-friendly water-based layer-by-layer assembly method. Specifically, renewable and biocompatible cellulose nanocrystals with electronegativity were used as the stabilizer to disperse multiwall carbon nanotubes (MWCNTs), meanwhile chitosan solution with rich positive charges was used as the effective “gluing” to enhance the interaction force between the monolayer MWCNTs. The resulting multilayer cracking-structured nanocomposites exhibited ultrahigh sensitivity with a gauge factor ∼359 and detection limit of ε = 0.5%. The samples maintained similar sensitivity even after 200 cycles of stretching/releasing. The high sensitivity is attributed to the disconnection-reconnection of the bioinspired spider-like microcrack junctions in MWCNTs layer. Moreover, the obtained strain sensor showed the abilities to detect not only large-scale body motions (finger bending) but also small-scale physiological strains induced by minute movements of muscles upon swallowing and smiling. It is promising to integrate this kind of strain sensors with human beings in future wearable devices and electronic skins.
3D-printed PEEK-Carbon Fiber (CF) composites: Structure and thermal properties Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-19 А.А. Stepashkin, D.I. Chukov, F.S. Senatov, A.I. Salimon, A.M. Korsunsky, S.D. Kaloshkin
CF-PEEK composites were manufactured by 3D-printing using a novel FDM methodology and customized printer and were compared with their cast counterparts. The characterization of composite thermal properties in the range 25–300 °C revealed that 3D-printed CF-PEEK composites manifest 25–30% lower thermal conductivity than cast composites. Short carbon fibers used for reinforcement showed orientation along the polymer flow both in cast and 3-D printed samples causing the anisotropy of thermal properties. The hierarchical nature of 3DP CF-PEEK porosity was observed by SEM imaging, which allowed the identification of large scale inter-layer gaps and cracks, and fine scale intra-layer defects that are likely to be induced by the thermal and mechanical gradients within the deposit that arise during fabrication. Purpose lay-up of long continuous carbon fibers during 3D-printing opens a way to fabricate tailored mechanical parts with desired anisotropy of thermal properties.
A novel approach to align carbon nanotubes via water-assisted shear stretching Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-17 Yingying Yu, Changhao Zhao, Qingwen Li, Jianying Li, Yuntian Zhu
Floating catalyst chemical vapor deposition (FCCVD) can produce buckypaper, a kind of CNT film, at large-scale with low cost. However, individual CNTs in the buckypaper are mostly randomly oriented, which significantly limits their electrical and mechanical properties. Here we report an innovative approach, water-assisted shear stretching (WASS), which can significantly improve CNT alignments and consequently enhance the electrical and mechanical properties. In addition, we define a unique “alignment factor” to quantify the alignment degree, and to estimate the effect of alignment on the mechanical and electrical properties of CNT assemblies. The high mechanical strength and excellent electrical conductivity of the WASS-processed buckypaper enhance their potential for applications in new electronic technologies and high-strength lightweight aerospace structures.
Synthesis of anhydrous manganese hypophosphite microtubes for simultaneous flame retardant and mechanical enhancement on poly(lactic acid) Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-05-16 Wei Yang, Wen-Jie Yang, Benjamin Tawiah, Yang Zhang, Li-Li Wang, San-E. Zhu, Timothy Bo Yuan Chen, Anthony Chun Yin Yuen, Bin Yu, Yun-Feng Liu, Jing-Yu Si, En-Zhu Hu, Hong-Dian Lu, Kun-Hong Hu, Qing Nian Chan, Guan Heng Yeoh
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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