Effect of thermal annealing on the crystalline structure of PVDF/PMMA-modified graphene nanocomposites

Abstract

Poly(vinylidene fluoride)-based nanocomposite films with different loadings of PMMA-modified graphene sheets were prepared by a solution-mixing and solvent casting method. The prepared films were annealed at three different temperatures and the crystalline structures of the samples were investigated. X-ray diffraction data confirmed the PMMA-modified graphene nanosheets enhanced the preferential β-crystalline structure when increasing the annealing temperature to 90?°C, while increasing the annealing temperature to 120?°C led to a β → γ phase conversion. The tendency of the graphene sheets to restack by increasing the annealing temperature was confirmed by XRD. The PMMA-modified graphene sheets, however, didn’t showa nucleating effect on the PVDF crystallizationduring DSC cooling scans.     

LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low‐density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1‐nm thickness and good transparency was synthesized using the well‐known Hummers's method. Fourier transform infrared and X‐ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are improved 65% and 92% by adding 7 wt% of GO and RGO, respectively. The tensile measurements showed that maximum tensile strength emerged in 3 wt% of loading for RGO and 5 wt% for GO. The measured oxygen and carbon dioxide permeability represented noticeably the attenuation of gas permeability in composite films compared with pristine LDPE/EVA blend. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of PVDF/MWNT,PMMA/MWNT,and PVDF/PMMA/MWNT nanocomposites: MWNT dispersibility and thermal and rheological properties

Pristine multi-walled carbon nanotubes (MWNTs) were incorporated into poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA), and PVDF/PMMA blends to achieve binary and ternary nanocomposites. MWNTs were more compatible with the PVDF matrix than with the PMMA-containing matrices. MWNT addition did not alter the development of α-form PVDF crystals in the binary/ternary composites. Nucleation and overall isothermal crystallization of PVDF were enhanced by the presence of MWNTs, and enhancements were optimal in the PVDF/MWNT binary composites. Avrami analysis revealed that addition of MWNTs led to more extensive athermal-type nucleation of PVDF, and that PMMA slightly decreased the crystal growth dimension of PVDF. The equilibrium melting temperature (T_m°) of PVDF increased in the binary composites but remained nearly constant in the ternary system. Thermal stability was enhanced in the binary/ternary composites, and enhancements were more evident in the air environment than in nitrogen. Rheological property measurements revealed that the intensely entangled chains of high-molecular weight PVDF dominated the rheological response of PVDF-included samples in the melt state. A (pseudo)network structure was developed in each of the PVDF-included samples as well as in the 1 phr MWNT-added PMMA/MWNT composite. The storage moduli of the PVDF, PMMA, and PVDF/PMMA:1/1 blend increased to 37%, 22% and 34%, respectively, at 40 °C after addition of 1 phr MWNT.     

Physical and mechanical properties of graphene oxide/polyethersulfone nanocomposites

The aim of this study was to investigate physical and mechanical properties of graphene oxide (GO)/polyethersulfone (PES) nanocomposite films. The films were produced by solution casting method. The mechanical properties of composite films were evaluated by tensile test. A significant enhancement in the mechanical properties of neat PES films was obtained incorporating a small amount of GO loading (0.05–1 wt.%). The highest tensile strength was observed at 1 wt.% of GO. Comparisons were made between experimental data and the Halpin–Tsai model predictions for the tensile strength and modulus of GO/PES composites. The effect of an orientation factor on model predictions was also acquired. The hydrophilicity of the nanocomposite was evaluated by assessing contact angle and enhanced wet ability of the films was obtained with increasing the amount of GO up to 1%. The morphology of the nanocomposites was investigated using scanning electron microscopy and transmission electron microscopy and the results revealed a good dispersion of GO in the PES matrix. The thermal behavior of the composite was also studied. Thermal stability of composites was increased by adding the GO. Copyright © 2013 John Wiley & Sons, Ltd.     

Dispersion of graphene oxide and its flame retardancy effect on epoxy nanocomposites

Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy.The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion,thermal stability and flame retardancy.X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix.Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy.The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.     

Polyimide nanocomposites based on functionalized graphene sheets: Morphologies,thermal properties,and electrical and thermal conductivities

Polyimide (PI) films were prepared by reacting 4,4′-(4,4′-isopropylidene-diphenoxy)-bis(phthalic anhydride) and 1,3-bis(4-aminophenoxy)benzene. The 4-phenylbutylamine-functionalized graphene sheets (PBA-GSs) used for the preparation of the PI nanocomposite films were prepared by mixing a dispersion of graphite oxide with a solution of the ammonium salt of 4-phenylbutylamine (PBA). PI nanocomposite films containing different amounts of PBA-GS (0–10 wt%) were compared in terms of their morphologies, thermal properties, and electrical and thermal conductivities. Only a small amount of PBA-GS was required to improve the thermal properties and thermal conductivities of the PI; the maximum enhancements in these parameters were observed at 1 and 3 wt% PBA-GS, respectively. In contrast, the electrical conductivity of the PI hybrid films continued to increase with increasing PBA-GS content from 1 to 10 wt%.     

Preparation and dielectric properties of composites based on PVDF and PVDF-grafted graphene obtained from electrospinning-hot pressing method

In this work, graphene was modified by the grafting of poly(vinylidene fluoride) (PVDF) using Friedel-Crafts reaction to form PVDF-grafted graphene (PGG) filler, which was confirmed by transmission electron microscope, Fourier transform infrared, Raman spectroscopy, wide angle X-ray diffraction, and thermogravimetric analysis. The solution containing as-prepared PVDF-grafted graphene and PVDF was electrospun to form fibrous membranes, which was subjected to hot pressing in the laminating mode to prepare solid PGG/PVDF composite films. The structures of electrospun fibrous membrane and solid PGG/PVDF composite film were investigated by scanning electron microscope. Furthermore, it could be found that the dielectric constants of PGG/PVDF composites exhibiting relatively low dielectric loss factors were significantly higher than that of pure PVDF.     

Effect of new melamine-terephthaldehyde resin modified graphene oxide on thermal and mechanical properties of PVC

In this study a new melamine-terephthaldehyde resin modified graphene oxide was synthesized and used as a reinforcement of poly(vinyl chloride) (PVC). Characterization, morphology, thermal and mechanical properties of the nanocomposites were examined by means of attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction, field emission-scanning electron microscopy, thermogravimetric analysis, differential scanning calorimeter and tensile properties. The first hydrochloric acid releasing data of poly(vinyl chloride) was removed by incorporation of the modified graphene oxide as compare to the neat polymer. The temperatures at 2 wt% losses, main decomposition temperatures, maximum decomposition temperatures, also shift to higher temperature in the corresponding nanocomposites as compared to the neat PVC. The tensile strength and elongation at break of the nanocomposite films was increased as compared to the neat PVC. The interesting results in crystallinity of PVC were observed with adding 5 wt% of the modified graphene oxide.     

Facile synthesis of Fe3O4/reduced graphene oxide/polyvinyl pyrrolidone ternary composites and their enhanced microwave absorbing properties

In this paper, ternary nanocomposites of Fe₃O₄/reduced graphene oxide/polyvinyl pyrrolidone (Fe₃O₄/rGO/PVP) as a novel type of electromagnetic microwave absorbing materials were synthesized by a three-step chemical approach. First, Fe₃O₄ nanospheres were made by solvent thermal method. Successively, the Fe₃O₄ particles were assembled with rGO after having activated by para-aminobenzoic acid. PVP grafting and reduction of GO happened simultaneously in the third step. It is found that the electromagnetic absorption (EA) performance of synthesized ternary composites with suitable PVP amount had been significantly enhanced comparing to Fe₃O₄ and Fe₃O₄/rGO. Merely 15?wt% low loading in paraffin and thin as 2.8?mm can reach effective EA bandwidth (below ?10 Db) of 11.2?GHz, and the highest reflection loss reached ?67?dB at 10.7?GHz. It was demonstrated that these composites show an effective route to novel microwave absorbing material design.     

A non‐covalent functionalization of copper tetraphenylporphyrin/chemically reduced graphene oxide nanocomposite for the selective determination of dopamine

A non‐covalent functionalization based on a copper tetraphenylporphyrin/chemically reduced graphene oxide (Cu‐TPP/CRGO) nanocomposite is demonstrated for selective determination of dopamine (DA) in pharmaceutical and biological samples. A homogeneous electron‐rich environment can be created on the graphene surface by Cu‐TPP due to the π–π non‐covalent stacking interaction. The synthesized Cu‐TPP/CRGO nanocomposite was characterized using scanning electron microscopy NMR, ultraviolet–visible and electrochemical impedance spectroscopies. The electrocatalytic activity of DA was evaluated using cyclic voltammetry and differential pulse voltammetry. The oxidation peak current (I_pa) of DA increased linearly with increasing concentration of DA in the range 2–200 μM. The detection limit was calculated as 0.76 μM with a high sensitivity of 2.46 μA μM^?1 cm ^{? 2}. The practicality of the proposed DA sensor was evaluated in DA hydrochloride injection, human urine and saliva, and showed satisfactory recovery results for the detection of DA. In addition, the Cu‐TPP/CRGO nanocomposite‐modified electrode showed excellent stability, repeatability and reproducibility towards the detection of DA. Copyright © 2015 John Wiley & Sons, Ltd.     

还原氧化石墨烯表面聚苯胺纳米阵列的制备及电化学电容性能

本文以阳极氧化铝(AAO)膜为模板,通过恒电位法在自组装还原氧化石墨烯(rGO)膜表面制备有序聚苯胺(PANI)纳米线阵列。通过拉曼光谱和场发射扫描电子显微镜分别对其结构和微观形貌进行了表征,并对PANI纳米线阵列的电化学电容性能进行了测试。结果表明,rGO膜表面可电沉积PANI,电沉积得到的PANI纳米线阵列具有比PANI薄膜材料更高的电容和比电容。     

Preparation of cobalt-tetraphenylporphyrin/reduced graphene oxide nanocomposite and its application on hydrogen peroxide biosensor

A novel cobalt-tetraphenylporphyrin/reduced graphene oxide (CoTPP/RGO) nanocomposite was prepared by a π–π stacking interaction and characterized by ultraviolet–visible absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The CoTPP/RGO nanocomposite exhibited high electrocatalytic activity both for oxidation and reduction of H₂O₂. The current response was linear to H₂O₂ concentration with the concentration range from 1.0 × 10⁻⁷ to 2.4 × 10⁻³ mol L⁻¹ (R = 0.998) at the reductive potential of −0.20 V and from 1.0 × 10⁻⁷ to 4.6 × 10⁻⁴ mol L⁻¹ (R = 0.996) at the oxidative potential of +0.50 V. The H₂O₂ biosensor showed good anti-interfering ability towards oxidative interferences at the oxidative potential of +0.50 V and good anti-interfering ability towards reductive interferences at the reductive potential of −0.20 V.     

Effect of electrostatic forces control on the structure and properties of polyaniline/graphene oxide nanocomposite

The effects of electrostatic forces (EF), control on the morphology, structure, and electrochemical properties of polyaniline, PANI/graphene oxide (GO), nanocomposites prepared by interfacial electropolymerization (IEP), are studied in this work. FESEM images showed that the IEP method can form the PANI/GO nanocomposites when the EF-control has been found mainly on the PANI nanofibers formation and growth on the GO film surface; and the EF-enhancement can form PANI nanofibers with small nano-diameter, longer length, uniform morphology, high order and well orientation as compared with the EF-reduction-formed sample. The EF-enhancement-formed PANI/GO nanocomposite showed improved electrochemical properties than that of the EF-reduction-formed sample due to the EF-enhancement that enhances the C–N structure for PANI/GO nanocomposite.     

Improved interfacial properties of PI composites through graphene oxide and carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs) have been identified as excellent nanoreinforcements for carbon fiber (CF)–reinforced polymers regarding a wide range of engineering applications. The outstanding properties of CNTs, such as their large surface area, high mechanical strength, and low manufacturing cost bring them to be distinguished nanoreinforcements for carbon fiber–reinforced polymers to form multifunctional and multiscale composites. Electrophoretic deposition of graphene oxide for CNTs onto the CF surface was conducted. The presence of graphene oxide–CNTs may effectively increase both the roughness and wettability of the CF surface, resulting in an improvement to the interfacial bonding strength between the CF and the polyimide (PI).     

Excellent photocatalytic reduction of nitroarenes to aminoarenes by BiVO4 nanoparticles grafted on reduced graphene oxide (rGO/BiVO4)

A novel heterogeneous composite material based on reduced graphene oxide (rGO) and bismuth vanadate (BiVO₄) was prepared and characterized by various techniques such as powder XRD, HRTEM, EADX, UV–Vis‐DRS, FT‐IR, Raman, BET and XPS analyses. The characterization results reveal that the rGO well decorated by BiVO₄. The electrochemical impedance spectroscopy (EIS) shows the increasing of charge transfer of rGO/BiVO₄ in presence of light irradiation. In this research, the pure BiVO₄ and rGO/BiVO₄ composite have been explored for photocatalytic reduction of nitroarenes. Among the prepared nanocomposites, rGO loaded with 10% BiVO₄ catalyst (noted as rGO/BiVO₄–10%) shows the best performance for the photo‐reduction of various nitroaromatic molecules to their corresponding amine compounds under visible‐light irradiation at room temperature. The catalyst exhibited in particular excellent photocatalytic activity for the conversion of 1,4‐dinitrobenzene to 4‐nitroanilline (100% conversion) in 20 min, 4‐chloronitrobenzene to 4‐chloroaniline and 2‐nitrophenol to 2‐aminophenol (100% conversion) in only 30 min. In addition, the conversion of 4‐bromonitrobenzene, 4‐iodonitrobenzene to their corresponding amine compounds (100% conversion) was achieved in 60 min. The catalyst was recovered for several times and reused without decreasing of its efficiency.     

Confinement effects on the thermal stability of poly(ethylene oxide)/graphene nanocomposites: A reactive molecular dynamics simulation study

Nonisothermal and isothermal decomposition of poly(ethylene oxide) (PEO) loaded with different concentrations of pristine graphene (PG) and graphene oxide (GO) nanoplatelets were investigated using reactive molecular dynamics simulation. The onset of nonisothermal decomposition of the PG‐loaded PEO system was the highest among all systems, suggesting that introducing PG to the polymer improves its thermal stability (an effect that increases with an increase in the PG concentration). At low concentration, introducing GO to the polymer brings about a deterioration of the thermal stability of the polymer consistent with experimental findings. On average, the activation energy for the isothermal decomposition of PG‐loaded PEO system increases by 60% over that of the neat PEO system, while it decreases by 40% for the GO‐loaded PEO system. A time‐dependent analysis of the through‐thickness decomposition profile of the above systems reveals that the polymer confined between the PG sheets exhibit a higher thermal stability compared to the bulk polymer. However, an opposite effect is observed with the polymer confined between the GO sheets. The latter observation is attributed to accelerated polymer chain scission in confined regions due to the ejection of reactive hydroxyl radicals from the GO surface during the early stages of thermal decomposition. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1026–1035     

Morphological,rheological, crystalline and mechanical properties of ethylene-vinyl acetate copolymer/linear low-density polyethylene/amphiphilic graphene oxide nanocomposites

Chemical modification of graphene oxide has become a popular method for imparting unique properties to extend its application. Here, we show a simple way to synthesize amphiphilic graphene oxide (AGO) by grafting quaternary ammonium salt onto GO sheets. The AGO sheets not only showed high thermal stability and good dispersion in many polar and non-polar solvents in comparison to GO sheets but also the chemical modification maintained the two-dimensional structure. As a result, the AGO sheets improve the interfacial interaction between ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE). Because of the large size of AGO, the location of AGO is very dependent on the mixing strategy. The AGO was dispersed in the EVA phase when AGO was mixed first with EVA and then with LLDPE, whereas it was confined in the LLDPE phase when AGO was mixed first with LLDPE and then with EVA. AGO sheets were found at the interface of LLDPE and EVA when AGO, EVA, and LLDPE were mixed together, suggesting that AGO has a high interfacial interaction with both LLDPE and EVA. These high interfacial interactions lead to high tensile strength, Young's modulus, complex viscosity and crystallization temperature in comparison to the EVA/LLDPE blends without AGO sheets.     

Copolyester/layered silicate nanocomposites: The effect of the molecular size and molecular structure of the intercalant on the structure and viscoelastic properties of the nanocomposites

The preparation of poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate)/layered silicate nanocomposites via a melt‐intercalation technique is reported. Layered silicates modified with different alkyl ammonium intercalants have been used for this purpose. A comparison is made between carefully chosen pairs of the nanocomposites, the choice depending on the cation‐exchange capacity or the intercalant concentration of the organically modified montmorillonite, to study the effects of the molecular size and molecular structure of the intercalant. The structure of the nanocomposites is characterized with wide‐angle X‐ray diffraction. The presence of well‐defined diffraction peaks and an observed increase in the interlayer spacing in the nanocomposites imply the formation of an intercalated hybrid. To investigate the viscoelastic behavior, these nanocomposites are also subjected to dynamic mechanical analysis. The dynamic mechanical properties show an increase in the storage modulus of the nanocomposites over the entire temperature range studied (except in the transition region from 68 to 78 °C) in comparison with that of the pristine polymer. The size of the intercalant molecule and the presence of functional groups capable of forming favorable interactions with the polymer govern the amount of polymer infiltrating the clay gallery space and control the increase in the modulus of the nanocomposite. The tan δ peak signifying the glass‐transition temperature shifts to lower temperatures in the nanocomposites. Interestingly, the nanocomposites show less damping than the pristine polymer. This behavior is understood in terms of the confinement of the polymer chains in the clay interlayer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3102–3113, 2003     

Experimental study on thermo-physical and rheological properties of stable and green reduced graphene oxide nanofluids: Hydrothermal assisted technique

In this study a dehydration hydrothermal technique has been used to introduce a simple, environmentally friendly and facile method for manufacturing highly dispersed reduced graphene oxide for improving the thermo-physical and rheological properties of heat transfer liquids. The hydrothermal reduction of graphene oxide was verified by various characterizations methods such as UV–visible absorption spectroscopy, Zeta potential, Raman spectroscopy, X-ray photoemission spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. A thorough investigation was conducted on the thermo-physical properties of reduced graphene oxide at concentrations of 0.02, 0.04, 0.06, and 0.08?wt% under different temperatures. Significant improvements in electrical and thermal conductivity were obtained by adding a small amount of hydrothermal-assisted reduced graphene oxide (h-rGO) in the suspension. The viscosity and density remained relatively unchanged with the increase of concentrations where the pH was maintained within the desirable value, despite the fact that no additive was used during the reduction process. It is noteworthy to highlight that the h-rGO aqueous suspensions have shown Newtonian behavior. Results indicated that the h-rGO could be employed as a promising additive for conventional heat transfer liquids for different thermal applications.     

Investigating the effect of ultrasonic irradiation on preparation and properties of conductive nanocomposites

In the present study, the ultrasonic irradiation technique was employed as a new approach to prepare 0-3-dimensional polyaniline/ZnO shell-core composite particles. By taking advantage of the multiple effects of ultrasound, one can break down the aggregates of nanocrystalline ZnO particles. The polymerization of aniline proceeded while the nanoparticles were redispersed by ultrasound, and the synthesized polyaniline deposited on the ZnO particle, which formed polyaniline-coated nanocrystalline composite particles. The material was characterized by using transmission electron microscopy, XRD, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). With increased ZnO content, the H-bonding interaction is strengthened and the characteristic peaks of benzoid and quinoid are shifted. X-ray photoelectron spectroscopy (XPS) shows that the ratio of the number of Zn and N atoms (Zn/N) on the surface is lower than that in the bulk. This is strong evidence for a PANI-encapsulated ZnO nanoparticles structure. The conductivity of the composites obtained through ultrasonic irradiation decreases with increasing ZnO content. Ultrasonic irradiation contributes to the increase in the conductivity compared with conventional stirring. Photocatalytic properties of PANI/ZnO nanocomposites were examined by degrading Reactive Black 5 (RB5) dye under visible light irradiation.