Formation of homogeneous nanocomposite films at ambient temperature via miniemulsion polymerization using graphene oxide as surfactant

A convenient and industrially scalable method for synthesis of homogeneous nanocomposite films comprising poly(styrene‐stat‐butyl acrylate) and nanodimensional graphene oxide (GO) or reduced GO (rGO) is presented. Importantly, the nanocomposite latex undergoes film formation at ambient temperature, thus alleviating any need for high temperature or high pressure methods such as compression molding. The method entails synthesis of an aqueous nanocomposite latex via miniemulsion copolymerization relying on nanodimensional GO sheets as sole surfactant, followed by ambient temperature film formation resulting in homogeneous film. For comparison, a similar latex obtained by physical mixing of a polymer latex with an aqueous GO dispersion results in severe phase separation, illustrating that the miniemulsion approach using GO as surfactant is key to obtaining homogeneous nanocomposite films. Finally, it is demonstrated that the GO sheets can be readily reduced to rGO in situ by heat treatment of the film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2289–2297     

Photo-induced Janus effect of graphene oxide films

The effect of UV irradiation on the wettability of GO films, as well as the possibility of making a film with different properties of its surface, the Janus film, has been studied. The O/C ratio changes from 0.32 to 0.26 after 6 ​h of UV irradiation. The contact angle of water droplet wetting on an unirradiated surface is θ ​≈ ​35°. The contact angle reaches more than 95° on the irradiated surface, which means that a hydrophobic surface on a film can be obtained. The origin of amphiphilic properties of the GO film are associated with the photochemical reduction of GO.     

Ethanol-assisted graphene oxide-based thin film formation at pentane-water interface

Graphene oxide (GO) can be viewed as an amphiphilic soft material, which form thin films at organic solvent-water interfaces. However, organic solvent evaporation provides little driving force, which results in slow GO transfer in aqueous phase, thus dawdling GO film formation processes for various potential applications. We present an ethanol-assisted self-assembly method for the quick formation of GO or GO-based composite thin films with tunable composition, transmittance, and surface resistivity at pentane-water interface. The thickness of pure GO and reduced GO (rGO) films ranging from ~1 nm to more than 10 nm can be controlled by the concentration of GO in bulk solution. The transmittance of rGO films can be tuned from 72% to 97% at 550 nm while the surface resistivity changes from 8.3 to 464.6 kΩ sq(-1). Ethanol is essential for achieving quick formation of GO thin films. When ethanol is injected into GO aqueous dispersion, it serves as a nonsolvent, compromising the stability of GO and providing driving force to allow GO sheets aggregate at the water-pentane interface. On the other hand, neither the evaporation of pentane nor the mixing between ethanol and water provides sufficient driving forces to allow noteworthy amount of GO sheets to migrate from the bulk aqueous phase to the interface. This method can also be extended to prepare GO-based composites thin films with tunable composition, such as GO/single walled carbon nanotube (SWCNT) composite thin films investigated in this work. Reduced GO/SWCNT composite films show much lower surface resistivity compared to pure rGO thin films. This ethanol-assisted self-assembly method opens opportunities to design and fabricate new functional GO-based hybrid materials for various potential applications.     

Shear-induced assembly of graphene oxide particles into stripes near surface

We report the shear-induced assembly of graphene oxide (GO) particles into periodic stripe-like patterns near the surface. These stripe-like patterns, which have an average periodic length of 100–250 μm, are aligned in a wavy manner along the normal to the flow direction. The self-assembled GO structures are investigated at different depths using three different analysis methods, namely, reflective microscopy observations of the photonic-crystalline GO dispersion, polarized optical microscopy, and fluorescence confocal laser scanning microscopy. The surface microstructures observed in reflection mode are different from the shear-induced band structures formed in bulk thermotropic liquid crystals and liquid crystal polymers, in terms of the shape and scale of the stripes. Further, there is also a difference in terms of the dependence of the stripe width on the shear rate. The observations suggest that the stripes are formed because of a competition between the stable surface-field-induced planar alignment of the GO particles near the surface and their relatively unstable shear-induced vertical alignment in the bulk. The findings of this study should advance our understanding of GO assembly under shear stress. Further, the proposed method is a novel one for inducing the assembly of GO particles into microstructures shaped as thread-like stripes.     

硒/氧化石墨烯/二氧化钛复合薄膜的制备及光电转换性质

将氧化石墨烯(GO)掺入钛酸溶胶中,以导电玻璃(ITO)为基底,经浸渍-涂覆-煅烧得到GO/TiO2复合薄膜;采用电沉积技术在GO/TiO2薄膜表面沉积Se纳米微粒,得到Se/GO/TiO2复合薄膜;利用扫描电子显微镜和X射线衍射仪分析了复合薄膜的形貌和晶体结构,采用紫外可见光谱仪测定了其光谱学性质,利用光电转换实验测定了其光电转换性质.结果表明,所制备的Se/GO/TiO2复合薄膜各组分分布均匀,具有锐钛矿相结构的TiO2颗粒粒径为20nm,与TiO2结合的GO具有分散片层结构,薄膜中的Se颗粒粒径为60～80nm.与此同时,在Se和GO的共同作用下,Se/GO/TiO2复合薄膜对可见光有很好的光电转换效应.     

Size fractionation of graphene oxide sheets by pH-assisted selective sedimentation

Graphene oxide (GO) sheets prepared by Hummers' method have been separated into two portions with large (f1) or small (f2) lateral dimensions from their aqueous dispersion. This method is based on the selective precipitation of GO sheets with lateral dimensions mostly (>90%) larger than 40 μm(2) at a pH value of 4.0 because of their larger hydrophobic planes and fewer hydrophilic oxygenated groups. The hydrazine reduced Langmuir-Blodgett (LB) films of f1 showed much higher conductivities than those of f2. Furthermore, the thin film of f1 prepared by filtration exhibited a smaller d-space and much higher tensile strength and modulus than those of f2 films. The one-step size fractionation method reported here is simple, cheap, efficient, and environmentally friendly, which can be used for the size fractionation of GO sheets in large scale.     

Thermal,mechanical and water barrier properties of graphene oxide/polyvinyl alcohol/polyol composite films

The novel polymer composite of polyvinyl alcohol (PVA), polyol(PO) and graphene oxide (GO) was used to prepare the PVA/PO and GO/PVA/PO with different weight percents of GO (0.5 and 1% denoted as (0.5 wt%)GO/PVA/PO and (1 wt%)GO/PVA/PO, respectively) through solution casting blend technique. The structure–properties of all used films were confirmed by scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and mechanical properties. The SEM results exhibited the uniform and homogeneous dispersion of GO in the PVA/PO blend matrix. The TEM and XRD analysis confirmed the structure and exfoliation of GO nanosheets, respectively. Thermal stability suggested that (0.5 wt%)GO/PVA/PO and (1 wt%) GO/PVA/PO films are more stable than PVA/PO. The tensile strength of (0.5 wt%)GO/PVA/PO and (1 wt%)GO/PVA/PO films reached 270.5% and 1349.6%, respectively, which are higher than that of the PVA/PO film. The decrease in the water absorption (WA) of GO/PVA/PO was found from 110.5 to 38.4%. The physico-mechanical properties of used films suggested that the prepared GO/PVA/PO blend composite films can be applied in food packaging areas.     

Efficient reduction of graphene oxide catalyzed by copper

We report that copper thin films deposited on top of graphene oxide (GO) serve as an effective catalyst to reduce GO sheets in a diluted hydrogen environment at high temperature. The reduced GO (rGO) sheets exhibit higher effective field-effect hole mobility, up to 80 cm(2) V(-1) s(-1), and lower sheet resistance (13 kΩ □(-1)) compared with those reduced by reported methods such as hydrazine and thermal annealing. Raman and XPS characterizations are addressed to study the reduction mechanism on graphene oxide underneath copper thin films. The level of reduction in rGO sheets is examined by Raman spectroscopy and it is well correlated with hole mobility values. The conductivity enhancement is attributed to the growth of the graphitic domain size. This method is not only suitable for reduction of single GO sheets but also applicable to lower the sheet resistance of Langmuir-Blodgett assembled GO films.     

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.     

Laser desorption/ionization mass spectrometric assay for phospholipase activity based on graphene oxide/carbon nanotube double-layer films

A new method for quantitative phospholipase activity assays using mass spectrometry (MS) and a supported thin film consisting of a graphene oxide (GO)/carbon nanotube (CNT) double layer as a substrate for laser desorption ionization (LDI) has been developed. Phospholipids were very efficiently analyzed by LDI-time-of-flight (TOF) MS on the GO/CNT films, presumably because of the affinity of phospholipids for the GO/CNT surface. Therefore, the rate of lipid hydrolysis was conveniently measured using LDI-TOF mass spectra obtained from a GO/CNT surface on which the phospholipid hydrolysis reaction mixtures had been spotted by comparing the mass-peak intensities of reactants and products. The present platform for phospholipase assays based on MS and GO/CNT double-layer films enables quantitative measurements at low cost, allows assays to be performed in a short time, and is compatible with an array format, unlike conventional assay methods.     

Surface modified graphene oxide/poly(vinyl alcohol) composite for enhanced hydrogen gas barrier film

A series of novel polyethyleneimine (PEI) modified graphene oxide (PEI-mGO) filled poly(vinyl alcohol) (PVA) nanocomposite (PEI-mGO/PVA) films were prepared by solution-casing for hydrogen gas barrier applications. Hydrophilic PEI was used to simultaneously reduce and modify graphene oxide sheets, thereby facilitating a homogeneous dispersion of PEI-mGO in the PVA matrix. The effects of PEI-mGO on the morphology and properties of the nanocomposite films were examined by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and field emission scanning electron microscopy. Analogous GO/PVA composites were also prepared and characterized for comparative purposes. The PEI-mGO/PVA nanocomposites showed higher thermal and mechanical stability as well as remarkable improvement in hydrogen gas barrier properties compared to the PVA film; specifically, the PEI-mGO/PVA film having 3.0 wt% of PEI-mGO content exhibited almost 95% decrease in GTR and permeability values compared to PVA film.     

Preparation and characterization of corn starch/soy protein biocomposite film reinforced with graphene and graphene oxide nanoplatelets

Corn starch (CS) and soy protein isolate (SPI), as inexpensive, abundant, and biodegradable materials, can chemically interact well with each other to produce biofilms. However, to overcome some of their physical and mechanical limitations, it is preferred to use their composite form, employing reinforcing materials. In this study, initially, graphene (G) and graphene oxide (GO) were synthesized by a green method. Then, to enhance the polymer blend final properties, the effects of adding G and GO in the range of 0.5 to 2 wt% on physical and mechanical properties of starch/protein blend were investigated. The results showed that the presence of 0.5‐wt% G and 2‐wt% GO significantly increased the modulus of starch/protein film from 252 to 578 and 449 MPa, respectively. In addition, the thermal stability of CS/SPI/GO (2 wt%) composite film was 50°C to 60°C more than that of the pure starch/protein film. On the other hand, G‐reinforced composite films tended to decline water diffusion compared with the pure polymer film. In addition, the composite film with 2‐wt% GO content had the lowest oxygen permeation rate (3.48 cm³ μm/m²d kpa) among the other composite films.     

Preparation of porous polyimide/in‐situ reduced graphene oxide composite films for electromagnetic interference shielding

Herein we report an easy and efficient approach to prepare lightweight porous polyimide (PI)/reduced graphene oxide (RGO) composite films. First, porous poly (amic acid) (PAA)/graphene oxide (GO) composite films were prepared via non‐solvent induced phase separation (NIPS) process. Afterwards PAA was converted into PI through thermal imidization and simultaneously GO dispersed in PAA matrix was in situ thermally reduced to RGO. The GO undergoing the same thermal treatment process as thermal imidization was characterized with thermogravimetric analysis, Raman spectra, X‐ray photoelectron spectroscopy and X‐ray diffraction to demonstrate that GO was in situ reduced during thermal imidization process. The resultant porous PI/RGO composite film (500‐µm thickness), which was prepared from pristine PAA/GO composite with 8 wt% GO, exhibited effective electrical conductivity of 0.015 S m^?1 and excellent specific shielding efficiency value of 693 dB cm² g^?1. In addition, the thermal stability of the porous PI/RGO composite films was also dramatically enhanced. Compared with that of porous PI film, the 5% weight loss temperature of the composite film mentioned above was improved from 525°C to 538°C. Moreover, tensile test showed that the composite film mentioned above possessed a tensile strength of 6.97 MPa and Young's modulus of 545 MPa, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of polycarbonate structure and reduction time on graphene oxide dispersion

Polycarbonate (PC)/graphene oxide (GO) composites with different GO reduction time and PC types were prepared by using a twin screw extruder at 260 °C after solution mixing with chloroform. The chemical reaction degree of PC/GO composites with GO reduction time was confirmed by C–H stretching peak at 3000 cm ^?1, and the chemical reaction degree decreased with GO reduction time. The slope for storage (G′) versus loss (G″) modulus plot decreases with an increase in heterogeneous property of the polymer melts. So we can check the GO dispersion of the PC/GO composites using by the slop for G′–G″ plot. According to the G′–G″ slopes for PC/GO composite with GO reduction time, GO was well dispersed within PC matrix when the reduction time decreased. It was re‐confirmed by atomic force microscope (AFM) results. Based on the degradation temperature by Thermogravimetric analysis, G′–G″ slopes, and surface roughness by AFM, the branched PC was better than linear PC for the GO dispersion within PC matrix. The fact was also confirmed by tensile test results that the Young's modulus increased with the improvement of GO dispersion. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation of the hybrid film of poly(allylamine hydrochloride)-functionalized graphene oxide and gold nanoparticle and its application for laser-induced desorption/ionization of small molecules

Hybrid films of gold nanoparticles and graphene oxides (GOs) were prepared by directly growing gold nanoparticles on supported thin layers of GO films on a glass slide. The gold/GO nanohybrid films were thoroughly investigated using various analytical methods, including Raman spectroscopy and atomic force microscopy. The hybrid film was then applied to laser desorption/ionization (LDI) of small molecules, which enabled mass spectrometric analysis of analytes. After a series of detailed mechanistic studies and systematic investigations, we found that the gold/GO hybrid films serve as a successful LDI platform for small-molecule analysis because of the high desorption efficiency of analytes from the hybrid films without inducing significant fragmentation of analytes. We suggest that the underlying GO films may effectively dissipate excess thermal energy generated by laser irradiation of Au to prevent undesirable analyte fragmentation.     

Influence of graphene oxide incorporation and chemical cross‐linking on structure and mechanical properties of layer‐by‐layer assembled poly(Vinyl alcohol)‐Laponite free‐standing films

Functional fillers in multilayered films provide opportunity in tailoring the mechanical properties through chemical cross‐linking. In this study, Laponite‐graphene oxide co‐dispersion was used to incorporate graphene oxide (GO) easily into polyvinyl alcohol (PVA)/Laponite layer‐by‐layer (LBL) films. The LBL films were found to be uniform and the layer thickness increased linearly with number of depositions. The process was extended to a large number of depositions to investigate the macroscopic mechanical properties of the free‐standing films. The LBL films showed remarkable improvements in mechanical properties as compared to neat PVA film. The GO‐incorporated LBL films displayed higher enhancements in the tensile strength, ductility, and toughness as compared to that of PVA/Laponite LBL films, upon chemical cross‐linking. This suggests the advantageous effects of GO incorporation. Interestingly, cross‐linking of LBL films for longer time period (>1 h) and higher temperature (～80 °C) was not found to be much beneficial. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2377–2387     

Chitin/graphene oxide composite films with enhanced mechanical properties prepared in NaOH/urea aqueous solution

Chitin/graphene oxide (GO) composite films with excellent mechanical properties were prepared in NaOH/urea solution using a freezing/thawing method. The structure, thermal stability and mechanical properties of the composite films were investigated. Use of an atomic force microscope and transmission electron microscopy indicated that GO was successfully exfoliated to a single layer by ultrasonication. The results revealed that GO nanosheets were homogeneously dispersed and embedded in the chitin matrix. Due to the strong interactions between GO and the chitin matrix, the tensile strength and elongation at break of the composite film possessing 1.64 wt% GO were significantly improved by 98.7 and 114.5 %, respectively, compared with pure chitin film.     

Incorporation of graphene oxide into cyclodextrin-dye supramolecular hydrogel

In this article, we report a cyclodextrin-templated, but polymer-free, supramolecular hydrogel incorporating Graphene oxide (GO), which, unlikely of other supramolecular assemblies, reveals a highly elastic behavior at an elevated temperature. The obtained supramolecular gel provides a uniform dispersion with high GO loading and long dispersion stability. Rheological experiments, in comparison to other supramolecular gels, reveal highly elastic characteristics of the hydrogel, exhibiting an increase in the storage modulus at around 35 °C and sturdy stability at an elevated temperature up to 50 °C. An investigation using a variety of analytical and characterization techniques demonstrates the effect of lithium ions on fine dispersion and complete reduction of GO inside gel matrix. The current finding is meaningful in the sense that the supramolecular gelation can be expanded to other nanomaterials, including carbon nanotubes and quantum dots. All of these features will make our supramolecular hydrogel useful in various applications, including biomedical release systems.     

Single-layered graphene oxide nanosheet/polyaniline hybrids fabricated through direct molecular exfoliation

In this study, we used direct molecular exfoliation for the rapid, facile, large-scale fabrication of single-layered graphene oxide nanosheets (GOSs). Using macromolecular polyaniline (PANI) as a layered space enlarger, we readily and rapidly synthesized individual GOSs at room temperature through the in situ polymerization of aniline on the 2D GOS platform. The chemically modified GOS platelets formed unique 2D-layered GOS/PANI hybrids, with the PANI nanorods embedded between the GO interlayers and extended over the GO surface. X-ray diffraction revealed that intergallery expansion occurred in the GO basal spacing after the PANI nanorods had anchored and grown onto the surface of the GO layer. Transparent folding GOSs were, therefore, observed in transmission electron microscopy images. GOS/PANI nanohybrids possessing high conductivities and large work functions have the potential for application as electrode materials in optoelectronic devices. Our dispersion/exfoliation methodology is a facile means of preparing individual GOS platelets with high throughput, potentially expanding the applicability of nanographene oxide materials.     

Approach to excellent superhydrophobicity and corrosion resistance of carbon-based films by graphene and cobalt synergism

A new series of carbon-based films doped with graphene oxide and cobalt (G-Co/a-C:H films) were successfully prepared on Si substrate via one-step electrochemical deposition of methanol as the carbon source and graphene oxide/cobalt as the dopant. G-Co/a-C:H films were fabricated at various graphene oxide concentration for comparative experiments. It can be found that the graphene oxide and cobalt were well embedded in amorphous carbon matrix to form superhydrophobic G-Co/a-C:H film at the doping GO concentration of 0.007 mg/mL, which was confirmed by transmission electron microscopy (TEM). It was noted that the superhydrophobicity of the resulting surface derives from its rough surface with hierarchical micro-nanostructures and the presence of the low-surface-energy GO components on it. The hierarchical micro-nanostructures are attributed to the corporate joint of GO and cobalt to form the multilevel nanoscale composite interface. Specially, the as-fabricated superhydrophobic G-Co/a-C:H film could exhibit excellent self-cleaning ability and corrosion resistance, revealed by the self-cleaning and corrosion tests.