Co-reporter:Guorui Wang, Xiaoli Li, Yanlei Wang, Zhiyue Zheng, Zhaohe Dai, Xiaoying Qi, Luqi Liu, Zhihai Cheng, Zhiping Xu, PingHeng Tan, and Zhong Zhang
The Journal of Physical Chemistry C November 22, 2017 Volume 121(Issue 46) pp:26034-26034
Publication Date(Web):November 7, 2017
DOI:10.1021/acs.jpcc.7b05771
It is fundamentally important to understand how the interlayer interaction of neighboring graphene sheets is influenced by chemical doping. Here we investigate the interlayer coupling of multilayer graphene doped with controlled boron content via the Raman-active in-plane shear mode. The experimental results reveal a remarkable decline in the interlayer shear modulus as boron content increases, which is a direct consequence of the enlarged interlayer spacing, further supported by the molecular dynamic (MD) simulations. Nanoindentation tests were conducted to clarify the influence of interlayer coupling behaviors on nanomechanical behaviors of boron-doped bilayer graphene. As the interlayer slippage is induced under shear deformations, the weakened shear resistance would lead to the reduced energy dissipation during sliding process. Our results provide valuable insight into fundamental mechanical properties of boron-doped graphene and its interfaces and potentially allows tailoring of interlayer coupling for low energy dissipation electromechanical devices.
Co-reporter:Guorui Wang, Enlai Gao, Zhaohe Dai, Luqi Liu, Zhiping Xu, Zhong Zhang
Composites Science and Technology 2017 Volume 149(Volume 149) pp:
Publication Date(Web):8 September 2017
DOI:10.1016/j.compscitech.2017.06.004
Interface failure is a common phenomenon for conventional composite materials when subjected to repeated mechanical loads, and it tends to be critical for nanocomposites due to several orders of magnitude enhancement in interfacial area. Herein, the graphene/poly(methyl methacrylate) (PMMA) interface when subjected to cyclic loading conditions exhibits obvious mechanical degradation through interfacial sliding, which has received little attention yet. Through a joint study of experimental tests and molecular dynamics simulations, the interface weakening is attributed to the formation of graphene buckles that not only reduces the interfacial contact area but also impairs the overall interfacial load transfer. However, reminiscent of the shape memory effect that is commonly triggered by temperature, conformational transition at the interfaces exhibits remarkable mechanical recovery under a moderate thermal stimulus, manifested by the interface reconstruction activated by van der Waals (vdW) forces. These findings elucidate the complex interactions between matrix and nanostructures in composite materials under cyclic loading conditions, and control over this mechanism could provide guidelines upon chemical design through tailoring the interfacial adhesion for specific applications.
Co-reporter:Weiwei Li, Mingji Chen, Zhihui Zeng, Hao Jin, Yongmao Pei, Zhong Zhang
Composites Science and Technology 2017 Volume 145(Volume 145) pp:
Publication Date(Web):16 June 2017
DOI:10.1016/j.compscitech.2017.03.009
A series of composite radar absorbing structures (RAS) with resistive frequency selective surface (FSS) have been designed and optimized in high efficiency using the transfer matrix method together with the adaptive genetic algorithm. The composite structures show broadband absorption property verified by both numerical simulation and experimental measurement. Especially, the optimal 5 mm-thick composite RAS inserted with a single layer of resistive FSS can produce 90% absorption bandwidth of around 11.8 GHz, which is much wider compared with the multilayered metallic metamaterial absorber with the same thickness. The composite RAS can be easily manufactured by dielectric substrates in combination with screen-printed resistive FSSs.
Co-reporter:Yan Tian, Hui Zhang, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2017 Volume 98(Volume 98) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.compositesa.2017.03.007
The effects of nanoparticles on interfacial properties between fiber and epoxy resin were evaluated based on micro- and macro-mechanical experiments, including micro-droplet, transverse fiber bundle tension and short-beam shear tests. All results indicated that the sol-gel-formed silica nanoparticles did improve the interfacial properties effectively. According to scanning electron microscope morphologies of fracture surfaces, these improvements were likely ascribed to the toughening effects of nanoparticles, i.e., nanoparticles offered better energy dissipation and more efficient stress transfer during fracture in the fiber/epoxy composites.
Co-reporter:Weiwei Li, Hao Jin, Zhihui Zeng, Liangpei Zhang, Hui Zhang, Zhong Zhang
Carbon 2017 Volume 121(Volume 121) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.carbon.2017.06.034
A type of flexible, broadband electromagnetic microwave absorber is designed, simulated, manufactured and characterized. The multilayer-structured absorber is composed of a screen-printed carbon-based resistive film sandwiched between two layers of silicon rubber/multi-walled carbon nanotube composites and in turn backed by aluminum foil. The theoretical analysis based on the equivalent circuit model and the electromagnetic simulations is instructive for the design of the absorbers with the desired operation frequency by simply tuning the thickness of the dielectric substrates and the utilization of the one carbon film. The absorber indicates a broadband absorption, with a 90% absorption bandwidth of 13.5 GHz, and the thickness of the dielectric substrate of 5 mm. The fabricated absorber also shows a flexibility that it can be bent, rolled and twisted without breakdown of the structure and degradation of the absorption performance.Download high-res image (313KB)Download full-size image
Co-reporter:Zhihui Zeng, Menglong Liu, Hao Xu, Yaozhong Liao, Feng Duan, Li-min Zhou, Hao Jin, Zhong Zhang, Zhongqing Su
Carbon 2017 Volume 121(Volume 121) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.carbon.2017.06.011
Strain sensing in an ultra-broadband frequency regime up to 400 kHz is obtained with developed lightweight and flexible carbon nanostructured polymer composites, in a frequency range far broader than any piezoresistive sensor previously reported. Various loadings, from static and low-frequency cyclic stretches, through high-frequency vibration, to ultrahigh-frequency ultrasonic guided waves, are applied for evaluation of the sensors' performance. Diverse content and type of carbon nanofiller, microstructure of the conductive network in the matrix, and electromechanical responses of the nanocomposites under broadband-frequency strain are discussed, in conjunction with dynamic mechanical analysis and a theoretical nanoscale model, to advance insight into the sensing mechanism of the sensors. Implementation of ultrasonic guided wave-based in-situ structural health monitoring using networked sensors made of carbon black/polyvinylidene fluoride nanocomposites indicates the significant application potential of the developed sensor to serve as an ultra-broadband and high-frequency responsive flexible strain sensor.Download high-res image (371KB)Download full-size image
Co-reporter:Weiwei Li;Mingji Chen;Hao Jin;Junchao Liu;Zhihui Zeng;Hui Zhang
Journal of Materials Chemistry C 2017 vol. 5(Issue 22) pp:5378-5386
Publication Date(Web):2017/06/08
DOI:10.1039/C7TC01091E
Flexible negative refractive index metamaterials (NIMs), composed of two conductive metallic layers separated by a 0.75 mm thick polyimide film, are fabricated using a simple and effective screen printing method. Benefiting from the ultra-high conductivity of the 3 μm silver (Ag) layers, the NIMs exhibit negative refraction on a wide frequency range of 3 GHz, whereas the thickness is only 0.756 mm. The NIMs show excellent flexibility with a minimum bending diameter of 20 mm without degradation of Ag layer, because of the strong adhesion between the Ag and the polymer substrate. Furthermore, these flexible NIMs show amazing stability at a temperature of 25 °C and a relative humidity of 30% for 10 months.
Co-reporter:Pengfei Chu, Hui Zhang, Jun Zhao, Feng Gao, Yufeng Guo, Bin Dang, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2017 Volume 99(Volume 99) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.compositesa.2017.03.036
It was found that metallic oxide nanoparticles may positively influence insulation properties of polymers working under high electric field. Herewith, four kinds of surface-modified silica nanoparticles were employed to fabricate epoxy nanocomposites. The surface properties of nanoparticles were characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis and contact angles. The effects of surface modification, filler fraction and test temperature on volume resistivity (ρv) of epoxy nanocomposites were studied. It was found that, at different test temperatures, the long-alkyl-modified nanoparticles resulted in higher ρv values of epoxy and less ρv sensitivity to temperature, compared to the short-alkyl-modified and hydroxyl-modified ones. The surface polarity of nanoparticles was found to correlate with the ρv values well. The surface modification may cause two possible mechanisms that affect the ρv values of the epoxy: (i) to offer the nanoparticles different levels of water absorption; (ii) to change the Maxwell-Wagner-Sillars polarization behaviors of the composites.
Co-reporter:Zhihui Zeng;Hao Jin;Mingji Chen;Weiwei Li;Licheng Zhou
Advanced Functional Materials 2016 Volume 26( Issue 2) pp:303-310
Publication Date(Web):
DOI:10.1002/adfm.201503579
Lightweight, flexible and anisotropic porous multiwalled carbon nanotube (MWCNT)/water-borne polyurethane (WPU) composites are assembled by a facile freeze-drying method. The composites contain extremely wide range of MWCNT mass ratios and show giant electromagnetic interference (EMI) shielding effectiveness (SE) which exceeds 50 or 20 dB in the X-band while the density is merely 126 or 20 mg cm−3, respectively. The relevant specific SE is up to 1148 dB cm3 g−1, greater than those of other shielding materials ever reported. The ultrahigh EMI shielding performance is attributed to the conductivity of the cell walls caused by MWCNT content, the anisotropic porous structures, and the polarization between MWCNT and WPU matrix. In addition to the enhanced electrical properties, the composites also indicate enhanced mechanical properties compared with porous WPU and CNT architectures.
Co-reporter:Yayun Liu, Jun Zhao, Lingyu Zhao, Weiwei Li, Hui Zhang, Xiang Yu, and Zhong Zhang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 1) pp:311
Publication Date(Web):December 7, 2015
DOI:10.1021/acsami.5b08766
A series of shape memory nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) E51/methylhexahydrophthalic anhydride (MHHPA)/multiwalled carbon nanotube (MWCNT) with various stoichiometric ratios (rs) of DGEBA/MHHPA from 0.5 to 1.2 and filler contents of 0.25 and 0.75 wt % are fabricated. Their morphology, curing kinetics, phase transition, mechanical properties, thermal conduction, and shape memory behaviors are systematically investigated. The prepared materials show a wide range of glass transition temperatures (Tg) of ca. 65–140 °C, high flexural modulus (E) at room temperature up to ca. 3.0 GPa, high maximum stress (σm) up to ca. 30 MPa, high strain at break (εb) above 10%, and a fast recovery of 32 s. The results indicate that a small amount of MWCNT fillers (0.75 wt %) can significantly increase all three key mechanical properties (E, σm, and εb) at temperatures close to Tg, the recovery rate, and the repetition stability of the shape memory cycles. All of these remarkable advantages make the materials good candidates for the applications in aerospace and other important fields.Keywords: carbon nanotube; curing; epoxy; nanocomposite; shape memory polymer
Co-reporter:Guorui Wang, Zhaohe Dai, Luqi Liu, Hai Hu, Qing Dai, and Zhong Zhang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 34) pp:22554
Publication Date(Web):May 25, 2016
DOI:10.1021/acsami.6b03069
The van der Waals (vdW) force dominated interface between graphene and polymer matrix creates weak points in the mechanical sense. Chemical functionalization was expected to be an effective approach in transfer of the outstanding performance of graphene across multiple length scales up to the macroscopic level, due to possible improvements in the interfacial adhesion. However, published works showed the contradiction that improvements, insensitivity, or even worsening of macro-mechanical performance have all been reported in graphene-based polymer nanocomposites. Particularly central cause of such discrepancy is the variations in graphene/polymer interfacial chemistry, which is critical in nanocomposites with vast interfacial area. Herein, O3/H2O gaseous mixture was utilized to oxidize monolayer graphene sheet with controlled functionalization degrees. Hydrogen bonds (H bonds) are expected to form between oxidized graphene sheet/poly(methyl methacrylate) (PMMA) at the interface. On the basis of in situ tensile-micro Raman spectroscopy, the impacts of bonding types (vdW and H-bonds) on both key interfacial parameters (such as interfacial shear strength and critical length) and failure modes of graphene/PMMA nanocomposite were clarified for the first time at the microscopic level. Our results show that owing to improved interfacial interaction via H bonds, the interface tends to be stiffening and strengthening. Moreover, the mechanical properties of the functionalized graphene/PMMA interface will be set by the competition between the enhanced interfacial adhesion and the degraded elastic modulus of graphene, which was caused by structural defects in the graphene sheet during the functionalization process and could lead to catastrophic failure of graphene sheets in our experimental observation. Our results will be helpful to design various nanofiller-based nanocomposites with high mechanical performance.Keywords: failure modes; functionalization; graphene; interface; Raman spectroscopy
Co-reporter:Zhihui Zeng, Mingji Chen, Hao Jin, Weiwei Li, Xiao Xue, Licheng Zhou, Yongmao Pei, Hui Zhang, Zhong Zhang
Carbon 2016 Volume 96() pp:768-777
Publication Date(Web):January 2016
DOI:10.1016/j.carbon.2015.10.004
A type of lightweight and flexible multi-walled carbon nanotube (MWCNT)/waterborne polyurethane (WPU) composites is fabricated, which show superior shielding effectiveness (SE) of electromagnetic interference in the X-band even under the thin thickness of samples. The thickness values 0.05, 0.32 and 0.8 mm correspond to SE of 24, 49 and 80 dB, respectively. This attributes to the extremely high MWCNT loading up to 76 wt%. Moreover, the composites show much higher specific SE (up to 3408 dB cm2/g) than other carbon-based polymer composites with similar filler amount. Shielding mechanisms of the composites with wide ranges of MWCNT loadings are discussed based on the concentration, thickness and conductivity. High concentration of MWCNT/WPU composites at low thicknesses indicates higher capability of shielding by absorption compared to reflection, which is adverse to composites with relatively low MWCNT mass ratios. A comparison between experimental and theoretical SE results is made in detail based on observed microstructures by scanning electron microscopy. The MWCNT/WPU composite films fabricated on large-area polyimide and cloth substrates are also demonstrated.
Co-reporter:Yanbing Zhang, Luqi Liu, Bing Sun, Guorui Wang, Zhong Zhang
Composites Science and Technology 2016 Volume 134() pp:36-42
Publication Date(Web):6 October 2016
DOI:10.1016/j.compscitech.2016.07.027
A facile, effective and environmental friendly route was presented to prepare lipophilic graphene oxide (GO) derivates via the esterification reaction of the carboxylate salt of GO and 1-bromohexadecane in the presence of a phase-transfer reagent in water. The resultant long alkyl chains modified graphene oxide sheets (GO-HD) show the long-term and stable dispersion capability in many organic solvents. Successful grafting of long alkyl chains onto GO surfaces was confirmed through FTIR, XPS, TGA, UV–vis spectrum techniques. Moreover, we utilized the GO-HD as a reinforcing filler to prepare GO-HD/thermoplastic polyurethane (TPU) nanocomposites through solution casting method. The uniform distribution and good interfacial adhesion are expected for the GO-HD based nanocomposites due to the good compatibility between long alkyl chains of GO-HD fillers and TPU chains. Notably, tensile mechanical tests demonstrated that the GO-HD/TPU nanocomposites at low filler contents (≤2 wt%) exhibit higher modulus, ultimate tensile strength without compromising the intrinsic extensibility of TPU matrix as compared with the GO/TPU nanocomposites with same filler content. Further, in situ tensile-micro Raman spectroscopy tests were employed to monitor the load transfer process at a microscopic level, and revealed the improved load transfer efficiency in the GO-HD/TPU nanocomposites.
Co-reporter:Zhaohe Dai, Guorui Wang, Luqi Liu, Yuan Hou, Yueguang Wei, Zhong Zhang
Composites Science and Technology 2016 Volume 136() pp:1-9
Publication Date(Web):18 November 2016
DOI:10.1016/j.compscitech.2016.09.005
There is increasing evidence in literature for significant improvements in both toughness and strength of graphene-based nanocomposites through engineering their nano-interfaces with hydrogen bonds (H-bonds). However, the underlying mechanical behaviors and properties of these H-bonded interfaces at the microscopic level were still not experimentally clarified and evaluated. Herein, this work reports a study on the interfacial stress transfer between a monolayer graphene and a commonly used poly(methyl methacrylate) (PMMA) matrix under pristine vdW and modified H-bonding interactions. A nonlinear shear-lag model considering friction beyond linear bonding was proposed to understand evolution of interfacial stresses and further identify key interfacial parameters (such as interfacial stiffness, strength, frictional stress and adhesion energy) with the aid of in situ Raman spectroscopy and atomic force microscopy. The present study can provide fundamental insight into the reinforcing mechanism and unique mechanical behavior of chemically modified graphene nano-interfaces and develop further a basis for interfacial optimal design of graphene-based high-performance nanocomposites.
Co-reporter:Pengfei Chu, Hui Zhang, Fenghua Chen, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2016 Volume 81() pp:34-40
Publication Date(Web):February 2016
DOI:10.1016/j.compositesa.2015.10.018
The different dispersion levels of silica nanoparticles in organic suspensions were deliberately fabricated using the bead milling technique by controlling the milling time. The dispersion level was confirmed by the dynamic light scattering technique, the transmission electron microscopy, the stability of the suspensions as well as the optical properties of the coatings made from the suspensions. The rheological behaviors of the suspensions were investigated by the steady and dynamic shear tests. It was found that larger agglomerations had a stronger impedence for suspension to flow, leading to a higher viscosity and stiffness. Some important rheological parameters were correlated with the dispersion levels of the suspensions and the reasonable explanation was discussed.
Co-reporter:Jun Kuang, Zhaohe Dai, Luqi Liu, Zhou Yang, Ming Jin and Zhong Zhang
Nanoscale 2015 vol. 7(Issue 20) pp:9252-9260
Publication Date(Web):10 Apr 2015
DOI:10.1039/C5NR00841G
Nanostructured carbon material based three-dimensional porous architectures have been increasingly developed for various applications, e.g. sensors, elastomer conductors, and energy storage devices. Maintaining architectures with good mechanical performance, including elasticity, load-bearing capacity, fatigue resistance and mechanical stability, is prerequisite for realizing these functions. Though graphene and CNT offer opportunities as nanoscale building blocks, it still remains a great challenge to achieve good mechanical performance in their microarchitectures because of the need to precisely control the structure at different scales. Herein, we fabricate a hierarchical honeycomb-like structured hybrid foam based on both graphene and CNT. The resulting materials possess excellent properties of combined high specific strength, elasticity and mechanical stability, which cannot be achieved in neat CNT and graphene foams. The improved mechanical properties are attributed to the synergistic-effect-induced highly organized, multi-scaled hierarchical architectures. Moreover, with their excellent electrical conductivity, we demonstrated that the hybrid foams could be used as pressure sensors in the fields related to artificial skin.
Co-reporter:Qing Liu, Luqi Liu, Ke Xie, Yuena Meng, Haiping Wu, Guorui Wang, Zhaohe Dai, Zhixiang Wei and Zhong Zhang
Journal of Materials Chemistry A 2015 vol. 3(Issue 16) pp:8380-8388
Publication Date(Web):09 Mar 2015
DOI:10.1039/C5TA00669D
Actuators can directly convert various types of energy into mechanical motions. In this work, we constructed a novel air working ionic actuator by sandwiching sulfuric acid–poly(vinyl alcohol) (H2SO4–PVA) gel electrolyte between two pieces of reduced graphene oxide/polyaniline (r-GO/PANI) nanocomposite film based electrode, in which the PANI nanoparticles were uniformly decorated onto the r-GO sheet surfaces through an in situ polymerization method. A combination of the supramechanical properties, electrical conductivity, large surface area of the individual graphene sheets and excellent electrochemical properties of the PANI component results in the composite electrode having good mechanical properties and a high electrochemical capacitance. Later tests indicated that the actuator could be stimulated under a low driving voltage (≤0.5 V) without trade-off actuator strokes, and showed excellent long-term actuation durability. Under a 0.5 V operating voltage, the actuation strain of the r-GO/PANI actuator could reach 0.327%, corresponding to a 30 MPa generated stress. We attribute the excellent actuation performance to the synergistic effect of the r-GO sheets and the PANI component.
Co-reporter:Ke Xie, Haiping Wu, Yuena Meng, Kun Lu, Zhixiang Wei and Zhong Zhang
Journal of Materials Chemistry A 2015 vol. 3(Issue 1) pp:78-82
Publication Date(Web):30 Oct 2014
DOI:10.1039/C4TA04671D
A novel metal-free hydrogen evolution reaction catalyst made of poly(3,4-dinitrothiophene)/SWCNT was developed. This catalyst presents a good hydrogen evolution reaction activity with a lower overpotential than metallic catalysts. Its performance was optimized to an overpotential of ca. 0.040 V and a hydrogen generation rate of 44.2 μmol h−1 cm−2.
Co-reporter:Guorui Wang, Luqi Liu, Zhaohe Dai, Qing Liu, Hong Miao, Zhong Zhang
Carbon 2015 Volume 86() pp:69-77
Publication Date(Web):May 2015
DOI:10.1016/j.carbon.2015.01.022
We systematically investigated the in-plane biaxial compression behavior of the monolayer poly (methyl methacrylate) (PMMA)/graphene/PMMA system by in situ Raman spectroscopy. The shifts of Raman G-band peak position exhibited three-stage features with increasing compressive strain, including elastic deformation, local Euler-buckling and continuous compression. Our results demonstrated that the mechanical stability of graphene based flexible electrodes greatly depended on the deformation modes, applied strain level and interfacial adhesion. The embedded graphene sheets performed reversible compressibility at lower strain level over many cycles. With further increasing compressive strain, the strain distribution of the embedded graphene sheet turned non-uniform, and the interfacial debonding occurred. An analytical model based on the mechanical instability theory was proposed to depict the interfacial debonding behavior of individual graphene sheet, which agreed well with the experimental results.
Co-reporter:Zhihui Zeng, Hao Jin, Liangpei Zhang, Hui Zhang, Zhuo Chen, Feng Gao, Zhong Zhang
Carbon 2015 Volume 84() pp:327-334
Publication Date(Web):April 2015
DOI:10.1016/j.carbon.2014.12.012
Multi-walled carbon nanotubes are used to fabricate a type of environment-friendly electrothermal bimetallic actuators with the matrix of waterborne polyurethane or silicone rubber. Even under a relatively low DC driven voltage of 7 V, the actuator can achieve a bending displacement up to 28 mm, or a curvature up to 0.29 cm−1, which are greater than most of other electrothermal actuators reported. The actuator has considerable controllability, large mechanical output and long life-time, and the working power can be reduced down to 25 mW/mm3 in the atmospheric environment. The actuation mechanisms owe not only to the mismatch in the coefficients of thermal expansion, but also to the unique negative temperature coefficient effect of nanotube composites. Furthermore, the bimetallic actuators based on various polymer matrices are supposed to provide revelations for electrothermal bimorph actuators.
Co-reporter:Jin-Hua Han, Hui Zhang, Peng-Fei Chu, Abolhassan Imani, Zhong Zhang
Composites Science and Technology 2015 Volume 114() pp:1-10
Publication Date(Web):19 June 2015
DOI:10.1016/j.compscitech.2015.03.012
Carbon nanotube (CNT) buckypaper (BP) is a kind of non-woven nano-fiber film with excellent mechanical and electrical properties. Herein, we applied it to enhance the tribological performance of epoxy resin. A relatively big BP film with a diameter up to 285 mm was obtained through a solution filtration method. The CNTs were surface-modified by ozone in order to improve their interfacial adhesion with the matrix. It was found that the CNTs were well impregnated by the epoxy resin and the interfacial adhesion was fairly good, especially for the modified ones. The wear tests were performed using a ball-on-disc (“steel-on-polymer”) configuration under dry sliding condition. Depending on the conditions of the wear tests, the frictional coefficient can be reduced from 0.71 of the neat resin down to 0.32 of ozone-modified BP/epoxy composite and the wear resistance can be improved by more than 4 times. The SEM morphologies and Raman spectra of worn surfaces for the samples were given to explain the possible wear micro-mechanisms. The BP/epoxy composites, even after subjected to harsh wear, still retained high electrical conductivity due to the robust CNTs network.
Co-reporter:Jin Shang, Yuli Chen, Yanguang Zhou, Luqi Liu, Guorui Wang, Xianglong Li, Jun Kuang, Qing Liu, Zhaohe Dai, Hong Miao, Linjie Zhi, Zhong Zhang
Polymer 2015 Volume 68() pp:131-139
Publication Date(Web):26 June 2015
DOI:10.1016/j.polymer.2015.05.003
•We investigate the influence of GO filler aspect ratios on mechanical properties of nanocomposites.•Embedded GO sheets with large lateral size easily form folded and crumpled microstructures inside matrix.•MD simulation indicate stress concentrations on the wrinkle throughout entire graphene area.•GO sheets with large aspect ratio degrade the mechanical performance of nanocomposites at a high stress level.Graphene and its chemical derivate have been taken as promising candidates in composites due to their extraordinary mechanical and physical properties. Different from conventional plate fillers, the embedded graphene fillers exhibit various morphologies (e.g. folded, crumpled, and distorted sheets) inside matrix because of its atomic thickness. In this work, we systematically investigated the influence of graphene oxide (GO) morphologies on the tensile properties of poly(vinyl alcohol)-based nanocomposites at low loading contents. Confocal laser scanning microscopy, as a characterization method, was employed to observe the morphologies of the embedded GO platelets. Tensile mechanical tests and in situ micro-Raman spectroscopy tests indicated that GO sheets with larger aspect ratios exhibited efficient interfacial load transfer and improved mechanical properties at ultra-low filler contents. However, with further increased nanofiller contents, the folded and crumpled GO sheets severely degraded the mechanical reinforcement as induced by interfacial debonding. Molecular dynamic simulation indicated obvious stress concentrations on the wrinkle throughout entire graphene platelet areas. Long-term creep tests confirmed the stress concentration eventually induced the decrease in creep resistance for nanocomposite at a high applied stress levels. All these results aided in understanding the mechanical behaviors of two-dimensional nanofiller-based nanocomposites with huge aspect ratios.
Co-reporter:B.X. Bie, J.H. Han, L. Lu, X.M. Zhou, M.L. Qi, Z. Zhang, S.N. Luo
Composites Part A: Applied Science and Manufacturing 2015 Volume 68() pp:282-288
Publication Date(Web):January 2015
DOI:10.1016/j.compositesa.2014.10.001
We investigate dynamic fracture of three types of multiwalled carbon nanotube (MWCNT)/epoxy composites and neat epoxy under high strain-rate loading (105–106105–106 s−1). The composites include randomly dispersed, 1 wt%, functionalized and pristine CNT/epoxy composites, as well as laminated, ∼50 wt% CNT buckypaper/epoxy composites. The pristine and functionalized CNT composites demonstrate spall strength and fracture toughness slightly higher and lower than that of neat epoxy, respectively, and the spall strength of laminated CNT buckypaper/epoxy composites is considerably lower; both types of CNTs reduce the extent of damage. Pullout, sliding and immediate fracture modes are observed; the fracture mechanisms depend on the CNT–epoxy interface strength and fiber strength, and other microstructures such as the interface between CNT laminates. Compared to the functionalized CNT composites, weaker CNT–epoxy interface strength and higher fiber strength lead to a higher probability of sliding fracture and higher tensile strength in the pristine CNT composites at high strain rates. On the contrary, sliding fracture is more pronounced in the functionalized CNT composites under quasistatic loading, a manifestation of a loading-rate effect on fracture modes. Despite their helpful sliding fracture mode and large CNT content, the weak laminate–laminate interfaces play a detrimental role in fracture of the laminated CNT buckypaper/epoxy composites. Regardless of materials, increasing strain rates leads to pronounced rise in tensile strength and fracture toughness.
Co-reporter:Qing Liu, Luqi Liu, Jun Kuang, Zhaohe Dai, Jinhua Han and Zhong Zhang
Nanoscale 2014 vol. 6(Issue 12) pp:6932-6938
Publication Date(Web):11 Apr 2014
DOI:10.1039/C4NR00536H
Actuator materials can directly convert different types of energy into mechanical energy. In this work, we designed and fabricated electrothermal air pump-type actuators by utilization of various nanostructured carbon materials, including single wall carbon nanotubes (SWCNTs), reduced graphene oxide (r-GO), and graphene oxide (GO)/SWCNT hybrid films as heating elements to transfer electrical stimulus into thermal energy, and finally convert it into mechanical energy. Both the actuation displacement and working temperature of the actuator films show the monotonically increasing trend with increasing driving voltage within the actuation process. Compared with common polymer nanocomposites based electrothermal actuators, our actuators exhibited better actuation performances with a low driving voltage (<10 V), large generated stress (tens of MPa), high gravimetric density (tens of J kg−1), and short response time (few hundreds of milliseconds). Besides that, the pump actuators exhibited excellent stability under cyclic actuation tests. Among these actuators, a relatively larger actuation strain was obtained for the r-GO film actuator due to the intrinsic gas-impermeability nature of graphene platelets. In addition, the high modulus of the r-GO and GO/SWCNT films also guaranteed the large generated stress and high work density. Specifically, the generated stress and gravimetric work density of the GO/SWCNT hybrid film actuator could reach up to more than 50 MPa and 30 J kg−1, respectively, under a driving voltage of 10 V. The resulting stress value is at least two orders of magnitude higher than that of natural muscles (∼0.4 MPa).
Co-reporter:Jin-Hua Han, Hui Zhang, Ming-Ji Chen, Guo-Rui Wang, Zhong Zhang
Composites Science and Technology 2014 Volume 103() pp:63-71
Publication Date(Web):28 October 2014
DOI:10.1016/j.compscitech.2014.08.015
Carbon nanotube buckypaper/thermoplastic polyurethane elastomer composites were successfully fabricated. At certain polyurethane contents, the composites exhibited simultaneous improvements in stiffness (up to 6 GPa), strength (up to 120 MPa), ductility (up to 30%) and toughness (up to 36 MJ/m3). The measured elastic modulus of the composites could be predicted by Mori–Tanaka model. The possible reinforcing mechanisms were discussed by Raman spectroscopy and SEM fractography. The results revealed that ductile polymers are very promising matrix in balancing the key mechanical properties of buckypaper, which are beyond the commonly used brittle thermosettings, e.g. epoxy resin.
Co-reporter:Juan Li;XiaoFei Shi;Feng Gao;LuQi Liu;Rui Chen
Science China Technological Sciences 2014 Volume 57( Issue 2) pp:239-243
Publication Date(Web):2014 February
DOI:10.1007/s11431-013-5453-5
In this study, the size distribution of atmospheric aerosol in Beijing was monitored by the scanning mobility particle sizer spectrometer and the optical particle sizer. The size of particles in atmospheric aerosol was primarily distributed in the range of less than 1 μm. It showed different changes with the mass concentrations of particulate matters with an aerodynamic diameter of ⩽2.5 μm (PM2.5) for different sizes of fine particles. The amount of ultrafine particles (less than about 60 nm) decreased while the larger ones (>60 nm) increased along with the mass concentration of PM2.5 in atmospheric aerosol. This was because of the formation of the secondary atmospheric aerosol. The polylactic acid (PLA) nanofibers were prepared for filtering the aerosol by electrospinning. PLA nanofiber mats were used as the middle layer to design the composite filter membranes. Atmospheric aerosol was used as dust source in the filtration test. The results showed that the filtration efficiency of the composite filter media increased along with the thickness of nanofiber mats, which was controlled by the collection time during electrospinning. Filtration efficiency can be improved obviously by compositing with a thin layer of nanofibers.
Co-reporter:Siting Ju, Hui Zhang, Mingji Chen, Chong Zhang, Xin Chen, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2014 Volume 66() pp:183-192
Publication Date(Web):November 2014
DOI:10.1016/j.compositesa.2014.07.003
Three silane coupling agents with amino, long alkyl chain or vinyl functional groups were used to modify magnesia (MgO) nanoparticles. The modified nanoparticles were then mechanically mixed with low-density polyethylene (LDPE) to fabricate insulating nanocomposites. The average size of the modified MgO aggregates dispersed in LDPE matrix was below 100 nm. The pulsed electroacoustic method indicated that the MgO nanoparticles regardless of surface modification were effective to suppress the packet-like charge injection and accumulation in the LDPE sample, decrease the permittivity and tan δ, and also improved the direct-current breakdown strength of LDPE at different temperatures. The best insulating properties were found in the case of vinyl-silane-modified-MgO/LDPE samples probably owing to the improved interfacial adhesion. A multi-core model was used to discuss the results obtained.
Co-reporter:Jun Kuang, Luqi Liu, Yun Gao, Ding Zhou, Zhuo Chen, Baohang Han and Zhong Zhang
Nanoscale 2013 vol. 5(Issue 24) pp:12171-12177
Publication Date(Web):17 Sep 2013
DOI:10.1039/C3NR03379A
A hierarchically structured thermal-reduced graphene (ReG) foam with 0.5 S cm−1 electrical conductivity is fabricated from a well-dispersed graphene oxide suspension via a directional freezing method followed by high-temperature thermal treatment. The as-prepared three-dimensional ReG foam has an ordered macroporous honeycomb-like structure with straight and parallel voids in the range of 30 μm to 75 μm separated by cell walls of several tens of nanometers thick. Despite its ultra-low density, the ReG foam has an excellent compression recovery along its in-plane direction. This property of the ReG foam can be attributed to its hierarchically porous structure, as demonstrated by the compression test. The excellent compression recovery and high conductivity provide the ReG foam with exceptional piezoresistive capabilities. The electrical resistance of the ReG foam shows a linearly decreasing trend with compressive strain increments of up to 60%, which cannot be observed in conventional rigid material-based sensors and carbon nanotube-based polymer sensors. Such intriguing linear strain-responsive behavior, along with the fast response time and high thermal stability, makes the ReG foam a promising candidate for strain sensing. We demonstrated that it could be used as a wearable device for real-time monitoring of human health.
Co-reporter:Yinglei Yue, Hui Zhang, Zhong Zhang, Yunfa Chen
Composites Science and Technology 2013 Volume 86() pp:1-8
Publication Date(Web):24 September 2013
DOI:10.1016/j.compscitech.2013.06.019
In this work the polymer–filler interaction between polydimethylsiloxane (PDMS) and fumed silica was discussed and a double-layer interfacial structure was established. Then excess energy and bound rubber were adopted to characterize the polymer–filler interaction. Bound rubber (BR) was measured by thermogravimetric analysis (TGA) of a series of extracted solids containing fumed silica particles and unextractable PDMS chains. Experimental results showed that the amount of bound rubber was slightly affected by filler’s dispersion but greatly affected by filler’s concentration, specific surface area and surface chemistry. It was also found that, due to the formation of constrained chains, bridging chains and occluded rubber, the amount of bound rubber could only roughly weigh the total polymer–filler interaction.
Co-reporter:Hui Zhang, Hui Zhang, Ling-yun Zhou, Christian Eger, Zhong Zhang
Composites Science and Technology 2013 Volume 88() pp:151-157
Publication Date(Web):14 November 2013
DOI:10.1016/j.compscitech.2013.08.024
Silica nanoparticles having different morphology and surface modification were used to prepare transparent polymeric coating samples. The dispersion level of nanoparticles, filler–matrix interface and abrasive wear tests were studied. Compared with the neat coating, all the nanocoatings exhibited significantly improved abrasive wear resistance at various testing conditions. By analyzing worn surfaces and profiles of the samples, such improvement was ascribed to the enhanced load-bearing ability and crack resistance of the nanocoatings. The morphology and surface modification of nanoparticles affected the wear resistance also. The pyrogenic nanoparticle-filled coatings were superior to colloidal ones in wear resistance, probably due to the fact that the aggregates had floc-like morphology, which may offer higher load-carrying ability, interlocking with matrix. When comparing the nanoparticles having the similar morphology, the filler–matrix interface will play a key role in wear resistance; the stronger interface corresponded to higher wear resistance.
Co-reporter:Ling-yun Zhou, Hui Zhang, Xiang-qiang Pei, Klaus Friedrich, Christian Eger, Zhong Zhang
Tribology International 2013 Volume 61() pp:62-69
Publication Date(Web):May 2013
DOI:10.1016/j.triboint.2012.11.021
The effects of some key parameters, i.e. impingement angle, erodent type, nanosilica content, nanosilica type, on the erosion behaviors of the polyacrylate-based coatings were systematically investigated. All samples showed brittle erosion behavior under erosion wear. When using the sharp-edged erodent, the mass loss of coatings decreased with the filler content, whereas it was not sensitive to the filler content when subjected to round erodents. Based on worn surface analysis, it was found that the sharp-edged erodent tended to cause micro-cutting and immediate micro-cracking on the coatings, whereas the round erodent would like to make micro-deformation on the coatings, and accordingly induce the surface fatigue. Moreover, the effect of nanoparticle type on the erosion wear was examined and discussed.Highlights► Polyacrylate-based coatings filled with nanosilica particles were prepared. ► Key parameters on the erosive resistance of the coatings were investigated. ► The angular erodent led to much greater mass loss of coatings than the round ones. ► The worn surfaces were analyzed and wear mechanisms were proposed. ► Type of nanoparticles on the erosive wear was discussed.
Co-reporter:Yinglei Yue, Hui Zhang, Zhong Zhang, Yunfa Chen
Composites Part A: Applied Science and Manufacturing 2013 Volume 54() pp:20-27
Publication Date(Web):November 2013
DOI:10.1016/j.compositesa.2013.06.016
Tensile properties of fumed silica filled hydroxylated polydimethylsiloxane (PDMS) networks were investigated in the current work. Similar to unfilled bimodal networks, unimodal networks filled with concentrated fumed silica exhibit non-Gaussian effect and improved ultimate tensile properties. The concept of “hierarchical network” was proposed to depict the networks exhibiting non-Gaussian effect at sufficiently high strains. It was found that the reinforcing effect originates from both the effective volume effect from filler volume and polymer–filler interaction and the synergistic effect between network chains within the “hierarchical network”. Experimental results showed that filler’s dispersion, concentration, specific surface area and surface chemistry have a great influence on the tensile properties, which could be interpreted by analyzing the variation of both effective volume effect and synergistic effect.
Co-reporter:Yinglei Yue, Chong Zhang, Hui Zhang, Donghai Zhang, Xin Chen, Yunfa Chen, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2013 Volume 53() pp:152-159
Publication Date(Web):October 2013
DOI:10.1016/j.compositesa.2013.06.005
Rheological behaviors of fumed silica filled hydroxylated polydimethylsiloxane suspensions were investigated in both static and dynamic shear modes. Both viscosity and modulus increase with filler’s concentration and specific surface area, however, they decrease with the improved dispersion and proper surface modification. In addition to the effective volume effect of filler’s excluded volume and polymer–filler interaction, the polymer-mediated filler–filler interaction contributes significantly. Such an interaction was classified according to the particle distance, and the concept of “inter-particle excess energy” was proposed. A combination of effective volume effect and inter-particle excess energy can be used to interpret the rheological behaviors of the nanocomposites.
Co-reporter:Dong Yan, Xiaofeng Li, Hui-Ling Ma, Xiu-Zhi Tang, Zhong Zhang, Zhong-Zhen Yu
Composites Part A: Applied Science and Manufacturing 2013 Volume 49() pp:35-41
Publication Date(Web):June 2013
DOI:10.1016/j.compositesa.2013.02.002
Multiwalled carbon nanotubes (MWNTs) were incorporated into polyamide 12 (PA12) and PA12/polyethylene-octene elastomer grafted with maleic anhydride (POE-g-MA) components by melt compounding. The addition of MWNTs improves electrical, dynamic mechanical and thermal properties of PA12. In the presence of 20 wt.% POE-g-MA, PA12/POE-g-MA/MWNT ternary nanocomposites exhibit substantially improved electrical conductivities as compared to PA12/MWNT binary nanocomposites with the same loading of MWNTs. The electrical conductivity shows 5–6 orders of magnitude increase in the percolation threshold region due to the volume exclusion effect of POE-g-MA. Variation of the compo unding sequence of the three components results in large difference in electrical conductivity of the ternary nanocomposites at the low loading of 2 wt.% MWNTs, while the difference becomes slight at high MWNT loading of 4 wt.%.
Co-reporter:Yun Gao, Mingyang Xie, Luqi Liu, Jinzhu Li, Jun Kuang, Wenjun Ma, Weiya Zhou, Sishen Xie, Zhong Zhang
Polymer 2013 Volume 54(Issue 1) pp:456-463
Publication Date(Web):8 January 2013
DOI:10.1016/j.polymer.2012.11.043
Carbon nanotube (CNT) fibers are a novel type of fibrous materials that show potential in polymeric composite fields. In this study, we investigated the interfacial behavior of a single single-walled carbon nanotube (SWCNT) fiber embedded in isotactic polypropylene (iPP) matrix. The SWCNT fibers were found to be able to act as a heterogeneous nucleating agent which inducing the formation of transcrystals around the fiber surface. According to the theory of heterogeneous nucleation, the interfacial free energy difference Δσ of iPP on the SWCNT fibers was determined and compared with that on the conventional fibers. By carefully controlling the crystallizing conditions, three types of α-iPP supra-molecular microstructures with different optical birefringences were obtained. Raman spectra were utilized to investigate the influences of the supra-molecular microstructures of the transcrystalline (tc) layer on the strain transfer efficiency from the matrix to the fibers at a microscopic level. Conventional single-fiber pull-out tests were further employed to compare with the results derived from the Raman tests.
Co-reporter:Zhaohe Dai, Yun Gao, Luqi Liu, Petra Pötschke, Jinglei Yang, Zhong Zhang
Polymer 2013 Volume 54(Issue 14) pp:3723-3729
Publication Date(Web):21 June 2013
DOI:10.1016/j.polymer.2013.05.013
•We investigated the creep-resistant behavior of MWCNT-PC nanocomposite fibers.•Creep resistance depended on the orientated degree of polymer chains and nanotubes.•Parametric studies were employed to understand the reinforcing mechanisms.•Polarized Raman spectroscopy evaluated the oriented degree of nanotubes.The influence of polymer chain orientation as well as multi-walled carbon nanotube (MWCNT) alignment on the creep-resistant behavior of nanocomposites has not been fully revealed yet. In this work, tensile and creep behaviors of MWCNT modified polycarbonate nanocomposite fibers produced by melt-spinning at different draw-down ratios have been studied at a temperature of 120 °C. For fibers with 2 wt.% MWCNTs, it was found that the Young's modulus and creep resistance show clear dependence on the orientation degree of the polymer chains and the alignment of the nanotubes. Parametric studies based on Burger's model and Weibull distribution function were employed to understand the reinforcing mechanisms. Polarized Raman spectroscopy was utilized to evaluate the orientation degree of nanotubes, and further to reveal the variation in alignment during creep deformation. The results show that Raman analysis was consistent with the creep results.
Co-reporter:Lingyun Zhou, Hui Zhang, Hui Zhang, Zhong Zhang
Particuology 2013 Volume 11(Issue 4) pp:441-447
Publication Date(Web):August 2013
DOI:10.1016/j.partic.2013.01.001
The homogeneous dispersion of nanoparticles in solvents or polymer matrices is essential for practical application of nanocomposites. In this study, the planetary ball milling technique was used to de-agglomerate silica nanoparticles in butyl acetate. The size of the nanosilica aggregates was evaluated by TEM and SEM. With the addition of polyacrylate polymer to the organic solvent, the nanoparticle agglomerates were effectively broken up by planetary ball milling at the proper milling time; however, re-agglomeration occurred after a longer milling time. The results of TGA and FTIR indicated that the polyacrylate molecules could be adsorbed in situ onto the nanoparticles. Behaving similar to a dispersant, the adsorbed polyacrylate reduced the blend viscosity significantly and prevented re-agglomeration of the nanoparticles. Utilizing the polyacrylate polymer both as the dispersant and the polymer matrix, the polyacrylate-based nanocoatings were further prepared. The optical transmittance and haze value of the nanocoatings were found to be sensitive to the dispersion level of the nanoparticles, and the elastic modulus and hardness of the nanocoatings were improved in comparison with those of the neat polymer coating.Graphical abstractPreparation of nanocoating with impurity-free dispersant.Highlights► A planetary ball milling was used to reduce the size of nanosilica agglomerates. ► Nanosilica/polyacrylate coating composites were prepared. ► Nanocomposites obtained exhibit good optical and mechanical properties.
Co-reporter:Dong Yan, Hao-Bin Zhang, Yu Jia, Juan Hu, Xian-Yong Qi, Zhong Zhang, and Zhong-Zhen Yu
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 9) pp:4740
Publication Date(Web):August 13, 2012
DOI:10.1021/am301119b
Electrically conductive polyamide 12 (PA12)/graphene binary nanocomposites with a low percolation threshold of 0.3 vol % were prepared by melt compounding. A rapid increase in electrical conductivity from 2.8 × 10–14 S/m of PA12 to 6.7 × 10–2 S/m was achieved with ∼1.38 vol % graphene. It is shown that graphene sheets were homogeneously dispersed in PA12 matrix. Furthermore, polyethylene-octene rubber grafted with maleic anhydride (POE-g-MA) was used to further enhance the electrical conductivity of PA12/graphene nanocomposites. Three compounding sequences were adopted to tailor the microstructure and properties of the ternary nanocomposites. Both highest electrical conductivity and storage modulus were obtained when most graphene sheets were located in PA12 matrix rather than in POE-g-MA phase.Keywords: electrical conductivity; graphene; melt compounding; nanocomposites; polyamide 12; selective localization;
Co-reporter:Long-Cheng Tang, Hui Zhang, Stephan Sprenger, Lin Ye, Zhong Zhang
Composites Science and Technology 2012 Volume 72(Issue 5) pp:558-565
Publication Date(Web):8 March 2012
DOI:10.1016/j.compscitech.2011.12.015
Epoxy composites filled with different amounts of aggregate-free silica nanoparticles and phase-separated submicron rubber particles were fabricated to study the synergistic effect of multi-phase particles on mechanical properties of the composites. Compared with binary composites with single-phase particles, the ternary composites with both rigid and soft particles offer a good balance in stiffness, strength and fracture toughness, showing capacities in tailoring the mechanical properties of modified epoxy resins. It was observed that debonding of silica nanoparticles from matrix in the ternary composites was less pronounced than that in the binary composites. Moreover, the rubber particles became smaller and their shape tends to be irregular, affected by the presence of rigid silica nanoparticles. The toughening mechanisms in the epoxy composites were evaluated, and the enlarged plastic deformation around the crack tip, induced by the combination of rigid and soft particles, seems to be a dominant factor in enhancing fracture toughness of the ternary composites.
Co-reporter:Qian-Yi Cheng, Ding Zhou, Yun Gao, Qi Chen, Zhong Zhang, and Bao-Hang Han
Langmuir 2012 Volume 28(Issue 5) pp:3005-3010
Publication Date(Web):January 14, 2012
DOI:10.1021/la204558f
We demonstrate the construction of three-dimensional graphene oxide based gel networks through the self-assembly of a series of amphiphilic molecules, which possess a polar carbohydrate headgroup attached to a nonpolar pyrene group. The gelation process can occur in both aqueous and organic solutions and be influenced by the gelators’ molecular structure. The driving forces for the gelation process were determined as π–π stacking and hydrogen bonding interaction by using fluorescence and infrared spectroscopies. Rheometry was used to investigate the mechanical properties of the hydrogels and the organogels. The hydrogel was investigated to be applied to remove dye from aqueous solution.
Co-reporter:Yu Jia, Zhimin Jiang, Jinping Peng, Xinglong Gong, Zhong Zhang
Composites Part A: Applied Science and Manufacturing 2012 Volume 43(Issue 9) pp:1561-1568
Publication Date(Web):September 2012
DOI:10.1016/j.compositesa.2012.04.011
Materials subject to cyclic stress can succumb to fatigue, causing failure at stress levels much lower than those in static loading cases. Herein we discussed the viscoelastic behaviors of polystyrene/multi-walled carbon nanotube (MWCNT) composites during short-term creep and recovery under tensile cyclic loading. Both unmodified and ozone oxidized MWCNTs were applied. It was found in general that the creep strain of thermoplastics dropped with decreasing temperature and stress, and with increasing content of carbon nanotubes. Moreover, with the increased cycle number, the creep strain reduced remarkably. This trend would be even more obvious at high levels of stress and temperature. Further mechanism analysis indicated the network-like structure formed by the molecule chains and nanotubes caused the reduction of the creep strain, the increasing of recovery ratio and the restriction on the mobility of amorphous molecule chains.
Co-reporter:Gang Liu;Hui Zhang;Dai-jun Zhang;Hui Zhang
Journal of Materials Science 2012 Volume 47( Issue 19) pp:6891-6895
Publication Date(Web):2012 October
DOI:10.1007/s10853-012-6633-6
Epoxy composite materials filled with nano-alumina particles were prepared by mechanical mixing techniques. The glass transition temperatures (Tg) of the nanocomposites were found to decline significantly with the increasing filler content. After the addition of 30-phr nanoparticles, the Tg of the filled sample decreased by as high as 55 °C, as compared with that of the neat epoxy polymer. Based on the selective adsorption hypothesis and the molecular diffusion, it is speculated that the hardener molecules were unevenly distributed in the nanocomposites, which caused imbalanced stoichiometry between the epoxy and the hardener and finally decreased the Tg. Some results that may support the adsorption hypothesis were given and discussed.
Co-reporter:Ke Peng, Lu-Qi Liu, Hongchao Li, Helmut Meyer, Zhong Zhang
Carbon 2011 Volume 49(Issue 1) pp:70-76
Publication Date(Web):January 2011
DOI:10.1016/j.carbon.2010.08.043
A method of carbon nanotubes (CNTs) oxidation at room temperature using ozone with added water vapor is described. The resulting CNTs were characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy. These show that more oxygenated functional groups could be grafted onto the CNT surfaces due to the addition of water vapor, compared to traditional approaches in which high density of ozone is required. The existed hydroxyl radicals in the water vapor/ozone mixture is considered to be responsible for the increased CNT oxidizing degree.Graphical abstractA controllable covalent functionalization of carbon nanotubes using an ozone/water vapor mixture, which has the features of low density of ozone and at room temperature. (Left: TEM of as received MWCNTs and right: TEM of MWCNTs functionalized using an ozone/water vapor mixture).Research highlights► A controllable covalent functionalization of CNTs is provided. ► An important factor, water, in the oxidation of CNTs was revealed. ► The oxidation of CNTs can be carried out at room temperature. ► Low purity of ozone is needed.
Co-reporter:Long-cheng Tang, Hui Zhang, Jin-hua Han, Xiao-ping Wu, Zhong Zhang
Composites Science and Technology 2011 Volume 72(Issue 1) pp:7-13
Publication Date(Web):6 December 2011
DOI:10.1016/j.compscitech.2011.07.016
This work focused on the fracture mechanisms and reinforcing effects of ozone-treated multi-walled carbon nanotubes (MWCNTs) in epoxy matrix. Ozone functionalization of MWCNTs was found to be of help for a better dispersion and stronger interfacial bonding with epoxy matrix, which in turn improve the strength and fracture toughness of the resin. The MWCNT/epoxy composites showed complicated failure modes than the conventional fibrous composites, which have been quantitatively investigated and correlated with the fracture toughness of the nanocomposites studied.Highlights► We focused on the reinforcing effects of ozone-treated carbon nanotubes in epoxy. ► Nanotubes perform better dispersion and stronger interfacial bonding with matrix. ► The mechanical properties of nanocomposites were significantly improved. ► The nanotube failure modes transferred from pullout to sliding-fracture. ► This failure mode favors the energy absorption and contributes to improved toughness.
Co-reporter:Hui Zhang, Hui Zhang, Longcheng Tang, Lingyun Zhou, Christian Eger, Zhong Zhang
Composites Science and Technology 2011 Volume 71(Issue 4) pp:471-479
Publication Date(Web):28 February 2011
DOI:10.1016/j.compscitech.2010.12.022
We applied two kinds of silica nanoparticles, i.e. colloidal and pyrogenic ones, to improve the performance of transparent coatings on polymer substrates. The urethane–acrylate oligomer was mixed with varied concentrations of silica nanoparticles, spin-coated onto polycarbonate substrate and finally cured by ultraviolet rays. The resultant thickness of the coatings can be controlled in the range of 20–30 μm. The transmission electron microscopy revealed that both silica nanoparticles presented different dispersion states, i.e. mono-dispersion for the colloidal nanoparticles and floc-like dispersion for the pyrogenic ones. In comparison with the colloidal nanoparticles filled coatings, the pyrogenic ones exhibited much improved modulus, hardness and wear resistance, but slightly decreased optical properties such as transmittance, haze and gloss. The nanoparticle morphology, amorphous structure, dispersion state and particle–matrix interfacial bonding relating to these properties were discussed in the present study.
Co-reporter:Hao Yan, Luqi Liu, Zhong Zhang
Materials Letters 2011 Volume 65(15–16) pp:2419-2421
Publication Date(Web):August 2011
DOI:10.1016/j.matlet.2011.04.091
Modified electrospinning apparatus has been developed for continually fabricating nanofiber staple yarns. For this purpose, a pair of rotating metal tubes was introduced to collect the aligned electrospun nanofibers and then twist them into yarns. Between the metal tubes, a rotating plastic tube was inserted to wind the yarns. By adjusting the rotation speed of all tubes, the twist of the nanofiber staple yarns can be controlled. The mechanical behaviors of polyacrylonitrile nanofiber staple yarns have been carried out as well. The results show that the nanofiber staple yarns hold excellent mechanical behaviors, which are capable of using as functional textile fabrics.
Co-reporter:Long-cheng Tang, Hui Zhang, Xiao-ping Wu, Zhong Zhang
Polymer 2011 Volume 52(Issue 9) pp:2070-2074
Publication Date(Web):19 April 2011
DOI:10.1016/j.polymer.2011.03.002
The failure analysis of reinforcing elements is of great significance to understand the structure-property relationship in polymer composites. Herein, we reported an improved methodology to ascertain and contrast the failure modes from one pair of homologous fracture surfaces of multi-walled carbon nanotubes (MWCNTs)/epoxy samples at high-magnification using scanning electron microscopy. Three possible failure modes of MWCNTs, i.e. pullout, immediate fracture and sliding-fracture, were proposed to account for the fractographic observation. Based on this approach, the failure modes of MWCNTs before and after surface modification were quantitatively discussed.
Co-reporter:Yun Gao, Lu-Qi Liu, Sheng-Zhen Zu, Ke Peng, Ding Zhou, Bao-Hang Han, and Zhong Zhang
ACS Nano 2011 Volume 5(Issue 3) pp:2134
Publication Date(Web):February 22, 2011
DOI:10.1021/nn103331x
High mechanical performances of macroscopic graphene oxide (GO) papers are attracting great interest owing to their merits of lightweight and multiple functionalities. However, the loading role of individual nanosheets and its effect on the mechanical properties of the macroscopic GO papers are not yet well understood. Herein, we effectively tailored the interlayer adhesions of the GO papers by introducing small molecules, that is, glutaraldehyde (GA) and water molecules, into the gallery regions. With the help of in situ Raman spectroscopy, we compared the varied load-reinforcing roles of nanosheets, and further predicted the Young’s moduli of the GO papers. Systematic mechanical tests have proven that the enhancement of the tensile modulus and strength of the GA-treated GO paper arose from the improved load-bearing capability of the nanosheets. On the basis of Raman and macroscopic mechanical tests, the influences of interlayer adhesions on the fracture mechanisms of the strained GO papers were inferred.Keywords: graphene oxide; interlayer adhesion; mechanical properties; Raman spectroscopy; strain transfer
Co-reporter:Yun Gao;Jinzhu Li;Luqi Liu;Wenjun Ma;Weiya Zhou;Sishen Xie
Advanced Functional Materials 2010 Volume 20( Issue 21) pp:3797-3803
Publication Date(Web):
DOI:10.1002/adfm.201001227
Abstract
High mechanical performances of macroscopic-scale fibers hierarchically constructed with carbon nanotubes (CNTs) are attracting great interest in the materials community owing to their merits of light weight and multiple functionalities. However, from the viewpoint of structural design, many fundamental issues, for example, modulus, strength, and deformation mechanisms of such CNT fibers are not yet well understood. In this Full Paper, the axial compression of hierarchical CNT fibers embedded in epoxy is investigated with the assistance of in situ Raman spectroscopy. Experimental results reveal that the conspicuous stiffening and strengthening effects of embedded CNT fibers are dominated by the constituent CNTs within the fiber, and have not yet been observed for conventional carbon fibers. Moreover, hierarchically structured CNT fibers exhibit notable flexibility without permanent deformation and failure under large-strain compression.
Co-reporter:Hui Zhang, Hui Zhang, Longcheng Tang, Zhong Zhang, Lei Gu, Youzhong Xu, Christian Eger
Tribology International 2010 Volume 43(1–2) pp:83-91
Publication Date(Web):January–February 2010
DOI:10.1016/j.triboint.2009.05.022
Hybrid nanocoatings are one of the most attractive topics in nanomaterials which have achieved the transition from fundamental researches to practical applications. In the present study, a urethane–acrylate oligomer was mixed with varied concentrations of nanosilica particle sol, spin-coated onto polycarbonate substrate and finally cured by ultraviolet (UV) rays. The morphology, mechanical properties and wear resistance of the resultant hybrid coatings were systematically investigated. Infrared spectroscopy (IR) analysis was performed to determine the eventual curing extent of the mixtures studied. The transmission electron microscopy (TEM) micrographs revealed almost perfect dispersion of the nanosilica particles within organic matrices, which ensured the excellent transparence of the hybrid coatings. Nanoindentation was further conducted to determine the mechanical properties, i.e. hardness, elastic modulus and their nanoparticle loading dependence. The short-term wear resistance was characterized by a pencil hardness tester. Moreover a universal micro-tribotester (UMT) was applied to investigate the long-term performance. As a result, about 20% decrease in coefficient of friction (COF) was achieved by the coating filled with 40 wt% nanosilica particles, compared to that of the unfilled coating. Under the same fretting test conditions, the wear rate in terms of wear volume of the hybrid coating containing 40 wt% nanoparticles was about 70 times lower than that of the neat coating, confirming the wear-reduction capability of the nanoparticles. The related wear mechanisms were discussed based on worn-surface observations.
Co-reporter:Yun Gao;LingYun Li;PingHeng Tan;LuQi Liu
Science Bulletin 2010 Volume 55( Issue 35) pp:3978-3988
Publication Date(Web):2010 December
DOI:10.1007/s11434-010-4100-9
Raman spectroscopy has been widely used to identify the physical properties of carbon nanotubes (CNTs), and to assess their functionalization as well as orientation. Recently, Raman spectroscopy has become a powerful tool to characterize the interfacial properties between CNTs and polymer matrices. This review provides an overview of micro-Raman spectroscopy of CNTs and its application in studying CNT reinforced polymer composites. Based on the specific Raman band shifts relating to the mechanical deformation of CNTs, Raman scattering can be used to evaluate the interactions between the CNTs and the surrounding polymer in the composites, and to detect the phase transitions of the polymer, and investigate the local stress state as well as the Young’s modulus of the CNTs. Moreover, we also review the current progress of Raman spectroscopy in various CNT macroarchitectures (such as films, fibers as well as composite fibers). The microscale structural deformation of CNT macroarchitectures and strain transfer factors from macroscale architectures to microscale structures are inferred. Based on an in situ Raman-tensile test, we further predict the Young’s modulus of the CNT macroarchitectures and reveal the dominating factors affecting the mechanical performances of the CNT macroarchitectures.
Co-reporter:Wenjun Ma, Luqi Liu, Zhong Zhang, Rong Yang, Gang Liu, Taihua Zhang, Xuefeng An, Xiaosu Yi, Yan Ren, Zhiqiang Niu, Jinzhu Li, Haibo Dong, Weiya Zhou, Pulickel M. Ajayan and Sishen Xie
Nano Letters 2009 Volume 9(Issue 8) pp:2855-2861
Publication Date(Web):July 8, 2009
DOI:10.1021/nl901035v
Carbon nanotubes have unprecedented mechanical properties as defect-free nanoscale building blocks, but their potential has not been fully realized in composite materials due to weakness at the interfaces. Here we demonstrate that through load-transfer-favored three-dimensional architecture and molecular level couplings with polymer chains, true potential of CNTs can be realized in composites as initially envisioned. Composite fibers with reticulate nanotube architectures show order of magnitude improvement in strength compared to randomly dispersed short CNT reinforced composites reported before. The molecular level couplings between nanotubes and polymer chains results in drastic differences in the properties of thermoset and thermoplastic composite fibers, which indicate that conventional macroscopic composite theory fails to explain the overall hybrid behavior at nanoscale.
Co-reporter:Zhenyu Jiang, Hui Zhang, Zhong Zhang, Hideki Murayama, Keiji Okamoto
Composites Part A: Applied Science and Manufacturing 2008 Volume 39(Issue 11) pp:1762-1767
Publication Date(Web):November 2008
DOI:10.1016/j.compositesa.2008.08.005
The interfacial bonding of carbon fiber and epoxy matrix modified by fullerene nanoparticles has been investigated using both transverse fiber bundle tension test and transverse tension test of unidirectional composites. It has been found that the incorporation of fullerene nanoparticles in a proper content, such as 2 wt%, led to a substantial increase in fiber/matrix bond strength. The improvement of interfacial bonding is ascribed to the toughening effect of epoxy matrix endowed by fullerene nanoparticles, which may contribute to suppress the fracture of interface layer around fibers by the mechanism of energy dissipation.
Co-reporter:Jinglei Yang;Klaus Friedrich;Alois K. Schlarb
Macromolecular Rapid Communications 2007 Volume 28(Issue 8) pp:955-961
Publication Date(Web):12 APR 2007
DOI:10.1002/marc.200600866
Poly(propylene) (PP) nanocomposites filled with shorter- and longer-aspect-ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin-screw extruder and an injection moulding machine. It is shown that with only 1 vol.-% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long-term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1 000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications.
Co-reporter:Olesja Starkova, Jinglei Yang, Zhong Zhang
Composites Science and Technology 2007 Volume 67(Issue 13) pp:2691-2698
Publication Date(Web):October 2007
DOI:10.1016/j.compscitech.2007.02.014
The long-term tensile creep of polyamide 66 and its nanocomposites filled with 1 vol.% TiO2 nanoparticles 21 and 300 nm in diameter is studied. It is assumed that the dominant mechanisms of creep deformation are of viscoelastic nature, while the contribution of plastic strains is not essential in the stress (< 0.6 of the ultimate stress) and time (about 100 hours) ranges considered. The creep isochrones obtained show that the materials exhibit a nonlinear viscoelastic behaviour and the degree of nonlinearity is reduced significantly by incorporation of the nanoparticles. The evolution of viscoelastic strains is less pronounced for the nanocomposite filled with smaller nanoparticles. Smooth master curves are constructed by applying the time–stress superposition (TSS). The Boltzmann–Volterra hereditary theory is used for the creep modeling. The nonlinearity of viscoelastic behaviour is taken into account by using the TSS principles and introducing a stress reduction function into an exponential creep kernel. The master curves are employed to predict the creep for time periods more than 60 times exceeding the test time. A comparison of relaxation spectra of the polymers shows that the incorporation of nanoparticles restricts the mobility of polymer chains. The smaller the nanoparticles, the greater the enhancement in the creep resistance. An empirical approach and a three-parameter law is also used for creep approximation. The efficiency of two models is evaluated by comparing their prediction validity.
Co-reporter:Zhenyu Jiang, Zhong Zhang, Klaus Friedrich
Composites Science and Technology 2007 Volume 67(Issue 2) pp:168-176
Publication Date(Web):February 2007
DOI:10.1016/j.compscitech.2006.07.026
An artificial neural network (ANN) technique is applied to predict the wear properties of polymer-matrix composites. Based on an experimental database for short fiber reinforced polyamide 4.6 composites, the specific wear rate, frictional coefficient and furthermore some mechanical properties, such as compressive strength and modulus, were successfully calculated by a well-trained ANN. 3-D plots for the predicted wear and mechanical characteristics as a function of material compositions and testing conditions were established. The results are in good agreement with measured data. It shows that the prediction accuracy is reasonable, and the network has potential to be improved if the experimental database for network training could be expanded.
Co-reporter:Hui Zhang, Zhong Zhang, Klaus Friedrich
Composites Science and Technology 2007 Volume 67(Issue 2) pp:222-230
Publication Date(Web):February 2007
DOI:10.1016/j.compscitech.2006.08.001
In this study, the influence of fiber length on tribological properties of short carbon fiber (SCF) reinforced epoxy composites was investigated. Both a block-on-ring and a pin-on-disk apparatus were applied for the study of sliding performance of composite specimens against polished steel counterparts under dry conditions. It was found that composites with longer SCF (nominal length = 400 μm) exhibited better wear resistance than those with shorter SCF (nominal length = 90 μm), in both cases either with or without graphite flakes and TiO2 nanoparticles. This effect seemed to be more pronounced at higher contact pressures applied. Furthermore, the steady frictional coefficient and contact temperature were reduced slightly by longer fibers. The relationships among the frictional coefficient, the contact temperature and the wear rate were discussed under the support of scanning electron microscope observations of the worn surfaces.
Co-reporter:Hui Zhang, Zhong Zhang
European Polymer Journal 2007 Volume 43(Issue 8) pp:3197-3207
Publication Date(Web):August 2007
DOI:10.1016/j.eurpolymj.2007.05.010
Multi-walled carbon nanotubes/polypropylene composites were compounded using a twin-screw extruder. Here, nanotubes with different lengths, i.e. 1–2 μm and 5–15 μm, respectively, were applied at a constant volume content of 1%. Notched Charpy impact tests showed that toughening effects of nanotubes depended highly on testing temperatures. The impact resistance was notably enhanced at a temperature above the glass transition temperature of matrix. Longer nanotubes performed more effective in toughening compared to the shorter ones. The increment of impact resistance of nanotube-filled polypropylene was considered due to enhanced load-carrying capability and much-increased deformation of matrix. SEM fractography further revealed the toughening mechanisms in a micro-scale. The impact energy was improved via nanotube breakage and pullout, which likely led to a series of energy consuming actions. In addition, the smaller spherulite size induced by nanotubes would be favourable to the impact resistance partially.
Co-reporter:Li Chang, Zhong Zhang, Lin Ye, Klaus Friedrich
Tribology International 2007 Volume 40(Issue 7) pp:1170-1178
Publication Date(Web):July 2007
DOI:10.1016/j.triboint.2006.12.002
The tribological properties of two kinds of high temperature resistant thermoplastic composites, polyetheretherketone (PEEK) and polyetherimide (PEI), reinforced with short carbon fibre (SCF), graphite flakes, and sub-micro particles of TiO2 and ZnS, were investigated in dry sliding conditions. Friction and wear experiments were conducted on a pin-on-disc apparatus, using composite pins against polished steel counterparts, performed within moderate pv-ranges at room and elevated temperatures (up to 150 °C). It was found that conventional fillers, i.e. SCF and graphite flakes, could effectively enhance both the wear resistance and the load-carrying capacity of the base polymers. With the addition of sub-micro particles, the frictional coefficient and wear rate of the composites were further reduced especially at elevated temperatures. On the basis of microscopic observation of worn surfaces, dominant wear mechanisms are discussed.
Co-reporter:Li Chang, Zhong Zhang, Lin Ye, Klaus Friedrich
Wear 2007 Volume 262(5–6) pp:699-706
Publication Date(Web):28 February 2007
DOI:10.1016/j.wear.2006.08.002
The multiple parts of this study are intended to experimentally and analytically elaborate the tribological properties of epoxy nanocomposites, reinforced by short carbon fibres (SCF), nano-TiO2 particles, polytetrafluorethylen (PTFE) powders and graphite flakes, in order to understand the role of fillers in modifying the wear behaviour of the materials. In this part, the influences of two solid lubricants, PTFE and graphite, were studied and compared. The transfer films established with two lubricants in sliding wear of epoxy nanocomposites against metallic counterparts were characterised under different sliding conditions. The morphology of transfer films was examined using scanning electronic microscopy (SEM), while their mechanical properties were investigated using micro-hardness tests. A method was proposed to determine the thickness of transfer films based on micro-indentation. The role of transfer films in dissipation of frictional heating was also studied. Epoxy nanocomposites containing both PTFE powders and graphite flakes showed a synergised effect in wear performance, especially under very severe wear conditions.
Co-reporter:Li Song, Hui Zhang, Zhong Zhang, Sishen Xie
Composites Part A: Applied Science and Manufacturing 2007 Volume 38(Issue 2) pp:388-392
Publication Date(Web):February 2007
DOI:10.1016/j.compositesa.2006.03.007
In this letter, the sandwich-like single-walled carbon nanotube (SWNT) paper/polyetheretherketone (PEEK) composites were successfully prepared by using a hot-compress method. Based on SEM observation, it was found that the PEEK macromolecules could diffuse into the voids of SWNT paper and were able to form very good bonding to the nanotube bundles, which ensure effective stress transfer between two phases. Some typical problems in preparing conventional carbon nanotube/polymer composites, e.g. the difficulty to obtain well-dispersed high-loading nanotubes into polymer matrices, were successfully overcome. Moreover, the compact networks of SWNTs were not destroyed at the appropriate processing condition. Correspondingly, the resulting composite (with one layer of SWNT paper) exhibited about 40% increased in Young’s modulus and 4% enhanced in failure strength when comparing with that of neat PEEK, respectively. According to rule-of-mixtures of the special sandwich-like structure, the estimated Young’s modulus can reach up to about 8 GPa, which was nearly three times of that of neat matrix. Moreover, the surface electric conductivity and thermal conductivity of the PEEK films were also increased after the addition of SWNT paper. The preliminary results suggest that the SWNT paper has great potential for being used to reinforce polymers.
Co-reporter:Hui Zhang, Zhong Zhang, Klaus Friedrich, Christian Eger
Acta Materialia 2006 Volume 54(Issue 7) pp:1833-1842
Publication Date(Web):April 2006
DOI:10.1016/j.actamat.2005.12.009
Abstract
SiO2/epoxy nanocomposites were formed in situ via a special sol–gel technique supplied by hanse chemie AG, in which silica nanoparticles with an average diameter of 25 nm were almost perfectly dispersed in the epoxy matrix. The static/dynamic modulus, microhardness, and fracture toughness of the nanocomposites were found to be enhanced with increasing silica content up to 14 vol.% (23 wt.%). The results confirmed that the homogeneously distributed nanoparticles are able to improve both the stiffness and toughness of the epoxy. Significant improvements were observed for both stiffness and toughness when the interparticle distance was smaller than the nanoparticle diameter. Under this condition, the interphase may construct a three dimensional physical network, which will finally dominate the performances of these nanocomposites. From the experimental observations, it is proposed that the critical thickness of the interphase surrounding a spherical nanoparticle is in the range of the particle’s radius, which is crucial to many modelling studies.
Co-reporter:L. Chang, Z. Zhang, H. Zhang, K. Friedrich
Tribology International 2006 Volume 38(11–12) pp:966-973
Publication Date(Web):November 2005–December 2006
DOI:10.1016/j.triboint.2005.07.026
The tribological behaviour of nano-TiO2 particle filled polyetherimide (PEI) composites, reinforced additionally with short carbon fibre (SCF) and lubricated internally with graphite flakes, was investigated. The wear tests were conducted on a pin-on-disc apparatus, using composite pins against polished steel counterparts under dry sliding conditions, different contact pressures and various sliding velocities. It was found that the conventional fillers, i.e. SCF and graphite flakes, could remarkably improve both the wear resistance and the load-carrying capacity. With the addition of nano-TiO2, the frictional coefficient and the contact temperature of the composite were further reduced, especially under high pv (the product of the normal pressure, p, and the sliding velocity, v) conditions. Based on microscopic observations of worn surfaces and transfer films on the counterparts, possible wear mechanisms were discussed.
Co-reporter:Yun Gao, Luqi Liu, Zhong Zhang
Acta Mechanica Solida Sinica (December 2009) Volume 22(Issue 6) pp:
Publication Date(Web):1 December 2009
DOI:10.1016/S0894-9166(09)60386-4
Nano-CaCO3 incorporated polystyrene composites are compounded by twin-screw extrusion. Tensile and compact tensile tests show that the strength and toughness of polystyrene are decreased after the addition of nano-CaCO3 particles. Fracture surface analysis suggests that the defects induced by interfacial debonding and nano-filler agglomerations would be the key factors responsible for the declined strength and toughness. Nevertheless, it has to be stated, if the applied stress is lower than the ultimate strength, the rigid nanoparticles would still stiffen the polymer molecules, and resist polymer chain mobility. Hence, the improved tensile modulus and creep resistance can be obtained with the increasing contents of nanoparticles.
Co-reporter:Yu Jia, Ke Peng, Xing-long Gong, Zhong Zhang
International Journal of Plasticity (August 2011) Volume 27(Issue 8) pp:1239-1251
Publication Date(Web):1 August 2011
DOI:10.1016/j.ijplas.2011.02.004
The creep and recovery of polypropylene/multi-walled carbon nanotube composites were studied. It was found for thermoplastics in general that the creep strain reduces with decreased temperature, and with enhanced content of carbon nanotubes. The incorporation of nanotubes improved the recovery property remarkably, especially at high temperature. The unrecovered creep strain of nanocomposites with content of 1 and 2.8 vol.% carbon nanotubes decreased by 53% and 73% compared to that of polymer matrix. To understand the mechanisms, the Burger’s model and Weibull distribution function were employed since the variations in the simulating parameters illustrated the influence of nano-fillers on the creep and recovery performance of the bulk matrix. To further study the recovery properties, the particular contribution of each Burger’s element to the total deformation was obtained and the recovery percentage was calculated. The time–temperature–superposition-principle was applied to predict the long-term creep behavior.
Co-reporter:Weiwei Li, Mingji Chen, Hao Jin, Junchao Liu, Zhihui Zeng, Hui Zhang and Zhong Zhang
Journal of Materials Chemistry A 2017 - vol. 5(Issue 22) pp:NaN5386-5386
Publication Date(Web):2017/05/09
DOI:10.1039/C7TC01091E
Flexible negative refractive index metamaterials (NIMs), composed of two conductive metallic layers separated by a 0.75 mm thick polyimide film, are fabricated using a simple and effective screen printing method. Benefiting from the ultra-high conductivity of the 3 μm silver (Ag) layers, the NIMs exhibit negative refraction on a wide frequency range of 3 GHz, whereas the thickness is only 0.756 mm. The NIMs show excellent flexibility with a minimum bending diameter of 20 mm without degradation of Ag layer, because of the strong adhesion between the Ag and the polymer substrate. Furthermore, these flexible NIMs show amazing stability at a temperature of 25 °C and a relative humidity of 30% for 10 months.
Co-reporter:Ke Xie, Haiping Wu, Yuena Meng, Kun Lu, Zhixiang Wei and Zhong Zhang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 1) pp:NaN82-82
Publication Date(Web):2014/10/30
DOI:10.1039/C4TA04671D
A novel metal-free hydrogen evolution reaction catalyst made of poly(3,4-dinitrothiophene)/SWCNT was developed. This catalyst presents a good hydrogen evolution reaction activity with a lower overpotential than metallic catalysts. Its performance was optimized to an overpotential of ca. 0.040 V and a hydrogen generation rate of 44.2 μmol h−1 cm−2.
Co-reporter:Qing Liu, Luqi Liu, Ke Xie, Yuena Meng, Haiping Wu, Guorui Wang, Zhaohe Dai, Zhixiang Wei and Zhong Zhang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 16) pp:NaN8388-8388
Publication Date(Web):2015/03/09
DOI:10.1039/C5TA00669D
Actuators can directly convert various types of energy into mechanical motions. In this work, we constructed a novel air working ionic actuator by sandwiching sulfuric acid–poly(vinyl alcohol) (H2SO4–PVA) gel electrolyte between two pieces of reduced graphene oxide/polyaniline (r-GO/PANI) nanocomposite film based electrode, in which the PANI nanoparticles were uniformly decorated onto the r-GO sheet surfaces through an in situ polymerization method. A combination of the supramechanical properties, electrical conductivity, large surface area of the individual graphene sheets and excellent electrochemical properties of the PANI component results in the composite electrode having good mechanical properties and a high electrochemical capacitance. Later tests indicated that the actuator could be stimulated under a low driving voltage (≤0.5 V) without trade-off actuator strokes, and showed excellent long-term actuation durability. Under a 0.5 V operating voltage, the actuation strain of the r-GO/PANI actuator could reach 0.327%, corresponding to a 30 MPa generated stress. We attribute the excellent actuation performance to the synergistic effect of the r-GO sheets and the PANI component.
