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, structure and properties of porous polyimide films via PAA/PU alloy

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption. Translated from Chemistry Journal of Chinese Universities 2006, 27(1): (in Chinese)     

Non‐surfactant template‐directed synthesis of SiO2‐polyimide hybrid self‐standing films with ordered mesoporous structure

The silica‐PI hybrid self‐standing films with ordered mesoporous structure have been prepared by using dibenzoyl‐L ‐tartaric acid (L ‐DBTA) as non‐surfactant template under mild sol–gel route. Polyimide matrix was obtained from polyamic acid (PAA) via thermal imidization process and the template was removed in this process. The PI‐based hybrid film with 20 wt% SiO₂ obtained from DBTA presented the ordered mesoporous channels with average pore size of about 2.0 nm and BET surface area of 1167 m²/g. FTIR and SEM studies indicated that the hydrogen bond interaction between the carboxylic groups of DBTA and benzamide bonds of PAA made the PAA possibly participate in the assembly process of the aggregates of the non‐surfactant template molecules. The mechanical, thermal and some physical properties of these hybrid films materials were also characterized. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Porous Molybdenum‐Based Hybrid Catalysts for Highly Efficient Hydrogen Evolution

We have synthesized a porous Mo‐based composite obtained from a polyoxometalate‐based metal–organic framework and graphene oxide (POMOFs/GO) using a simple one‐pot method. The MoO₂@PC‐RGO hybrid material derived from the POMOFs/GO composite is prepared at a relatively low carbonization temperature, which presents a superior activity for the hydrogen‐evolution reaction (HER) in acidic media owing to the synergistic effects among highly dispersive MoO₂ particles, phosphorus‐doped porous carbon, and RGO substrates. MoO₂@PC‐RGO exhibits a very positive onset potential close to that of 20 % Pt/C, low Tafel slope of 41 mV dec^?1, high exchange current density of 4.8×10^?4 A cm^?2, and remarkable long‐term cycle stability. It is one of the best high‐performance catalysts among the reported nonprecious metal catalysts for HER to date.     

In‐Situ “molecular welding” preparation of graphene/polyimide hybrid film with superior thermal conductivity and flexibility

With the rapid development of electronic industry, thermal management has become a critical issue that severely restricts the application of portable devices. In this work, we fabricate a flexible and free‐standing graphitized‐graphene/polyimide (I‐g‐GO/PI) film via an in‐situ “molecular welding” strategy. With the help of in‐situ polymerization, PI can be well‐dispersed with GO and serves as a solder to enlarge the grain size of GO, resulting in an enhanced thermal conductivity of the film. The 7 wt % addition of PI into GO (I‐g‐GO/PI‐7%) leads to an in‐plane thermal conductivity as high as 1269.700 ± 1.498 W/m/K, which is 81.8% higher than that of the pristine graphene and also superior to that fabricated via solution blending method by 58.3%. Simultaneously, the hybrid film exhibits an excellent flexibility and survives from a 2000 cycles bending test. The large‐area hybrid film prepared by such an in‐situ “molecular welding” method provides a promising way to fabricate graphene‐based film for highly efficient thermal management. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1215–1223     

The reduction of graphene oxide by elemental copper and its application in the fabrication of graphene supercapacitor

In this work, graphene oxide (GO) was directly reduced by copper to reduced graphene oxide (RGO) and formed a highly uniform RGO film on copper foil or copper-modified titanium (Ti) substrate. The characterization of as-prepared RGO film by FTIR and XRD indicated that GO was partially reduced by copper while some oxygen-containing groups still remained. The conductivity of the RGO film was improved from 3.76?×?10³ to 2.98?×?10⁴ S/m after it was further electrochemically reduced due to the removal of additional oxygen groups. The graphene supercapacitor prepared with this method exhibited better performances in a neutral aqueous electrolyte compared with that reported for graphene electrodes prepared by other fabrication methods.     

Nanostructure Restoration of Thermally Reduced Graphene Oxide Electrode upon Incorporation of Nafion for Detection of Trace Heavy Metals in Aqueous Solution

High performance reduced graphene oxide (RGO)‐Nafion (N) thin film electrodes coated on silicon (Si) substrates (RGO‐N/Si) were successfully developed through thermal reduction of GO‐N without delamination from the substrates. The restoration of the RGO‐N nanostructure upon the addition of Nafion was proven by Raman spectroscopy (RS) and field emission scanning electron microscopy, and the restoration mechanism of the RGO‐N nanostructure was proposed. Through the investigation using x‐ray photoelectron spectroscopy (XPS), the polyfluorocarbon from Nafion possessed a function that could prevent the delamination of the RGO sheets from the substrates during the thermal reduction. The RGO‐N/Si samples were later used for the determination of trace heavy metals, such as divalent lead, cadmium and copper ions (Pb²⁺, Cd²⁺ and Cu²⁺, respectively) using square wave anodic stripping voltammetry in a 0.1 M acetate buffer solution (pH 5). Based on the electroanalytical measurements, the RGO‐N/Si samples exhibited a highly linear behavior in the detection of Cd²⁺, Pb²⁺ and Cu²⁺ over the concentration range of 50 nM to 300 nM with detection limits at nM levels. In addition, the RGO‐N/Si samples presented good recoveries of target metals in tap water samples.     

Using a polyelectrolyte to fabricate porous polyimide nanoparticles with crater‐like pores

We have used the reprecipitation method and subsequent two‐step imidization to fabricate highly porous polyimide (PI) nanoparticles possessing crater‐like surface pores (depths, diameters: tens of nanometers) from poly(amic acid) (PAA) derivatives in the presence of poly(sodium‐4‐styrenesulfonate) (PSS) as a polyelectrolytic porogen. The porous structures arose presumably through segregative microphase separation of PAA and PSS (i.e. repulsion between PAA and PSS in the presence of a common solvent) and subsequent removal of PSS. The addition of this strong polyelectrolyte improved the degree of porosity of the resulting PI nanoparticles and allowed controllable release of the porogen. The resulting porous PI nanoparticles exhibited a high thermal stability (5% weight loss at temperature 450°C). This technique is suitable for the preparation of novel low‐k materials and their surface‐related applications. Copyright © 2008 John Wiley & Sons, Ltd.     

The Preparation of Compressible and Fire‐Resistant Sponge‐Supported Reduced Graphene Oxide Aerogel for Electromagnetic Interference Shielding

We here report a facile method to fabricate a sponge‐supported reduced graphene oxide aerogel (S‐RGOA) using a commercial melamine sponge and graphene oxide (GO). Firstly, GO sheets were self‐assembled within the melamine sponge by the assistance of a chemical cross‐linking agent; and then, freeze‐drying and thermal treatment were adopted to prepare S‐RGOA, in which continuous porous reduced graphene oxide (RGO) network formed between the skeleton. The resulting S‐RGOA exhibited a high electromagnetic interference shielding effectiveness (EMI SE) of 20.4‐27.3 dB in 8–12 GHz and the specific EMI SE could reach 1437 dB?cm³g^?1. The mechanical test suggests that the lightweight S‐RGOA is compressible and possesses low energy dissipation. Burning and TGA measurements indicate that S‐RGOA is fire‐resistant and has excellent thermal stability. Our work provides an economical and environmentally‐friendly method to fabricate RGO aerogels for using as electromagnetic interference materials.     

Studies on polyimide imidization in far‐infrared radiation

In this paper, the monomers 4,4′‐oxydiphthalic anhydride (ODPA), 3,3′,4,4′‐biphenyl dianhydride (BPDA), 3,4′‐oxidianiline (3,4′‐ODA), and 4,4′‐oxidianiline (4,4′‐ODA) were selected to synthesize polyimides (PI) or copolyimides (co‐PI) in N,N‐dimethyl acetamide (DMAc) by two‐step method. To control the PI molecular weight (MW), phthalic anhydride (PA) was used as the end‐capping reagent. The effect of far‐infrared radiation (FIR) on PI imidization was investigated by Fourier transform infrared spectroscopy (FTIR). Some factors affecting imidization process in FIR were discussed, including PI imidization time and temperature, molecular structure, designed number average molecular weight, crystalline, imidization procedure, film thickness, polyamide acid (PAA) solid content, and so forth. The PI imidization process in FIR will be affected by all these factors. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3621–3627, 2005     

Design and synthesis of optically transparent calcium‐incorporated polymer complexes

Transparent thin films of calcium‐ion‐incorporated polymer composites were synthesized with calcium carbonate (CaCO₃) and polymers such as poly(acrylic acid) (PAA), poly(ethylene glycol) (PEG), and methylcellulose. The homogeneous distribution of Ca²⁺ in the composite films was observed because of the high concentration of COO^? groups along the PAA backbone for the complexation of Ca²⁺ ions. The optical transparency of the composites depends on the weight percentages of the three polymers and the molar concentration of CaCO₃ in the composites. Maximum transparency was obtained for a composite film with a PAA/CaCO₃ ratio of 9:1. The results indicated that methylcellulose improved the film‐forming capabilities and that PEG improved the transparency of the composites. All polymer complexes were characterized with X‐ray diffraction, fourier transfer infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, dynamic mechanical analysis, and optical transparency measurements. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4459–4465, 2004     

Thermal kinetics and thermo‐mechanical properties of graphene integrated fluoroelastomer

In this work, the thermal properties of a fluoroelastomer enhanced by graphene were systematically investigated. Although graphene oxide (GO) is the most popular and cheapest source for graphene, its chemical and thermal properties were quite different from reduced graphene oxide (RGO). By comparing their influences on the thermal properties of elastomer, the effects from chemical structures and morphologies of graphene were analyzed. As the vulcanization and decomposition determine the properties of the elastomer proved by significantly different thermo‐mechanical properties of the fluoroelastomer reinforced by GO and RGO presented, this work provides a method to ultimate utilize graphene to reinforce elastomer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1691–1700     

Preparation of Molecularly Imprinted Electrochemical Sensor for Detection of Vincristine Based on Reduced Graphene Oxide/Gold Nanoparticle Composite Film

An innovative molecularly imprinted electrochemical sensor was fabricated based on reduced graphene oxide (RGO) and gold nanocomposite (Au) for rapid detection of vincristine (VCR). The RGO‐Au composite membrane was obtained via direct one‐step electrodeposition technique of graphene oxide (GO) and chloroauric acid (HAuCl₄) on the surface of a glassy carbon electrode (GCE) by means of cyclic voltammetry (CV) in the potential range between ?1.5 and 0.6 V in phosphate buffer solution (PBS) of pH 9.18, which is capable of effectively utilizing its superior electrical conductivity, larger specific surface area due to its synergistic effect between RGO and Au. The molecularly imprinted polymers (MIPs) were synthesized on the RGO‐Au modified glassy carbon electrode surface with VCR as the template molecular, methyl acrylic acid (MAA) as the functional monomer, and ethylene glycol maleic rosinate acrylate (EGMRA) as a cross‐linker. The performance of the sensor was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) in detail. Under the optimum conditions, the fabricated sensor exhibited a linear relationship between oxidation peak current and VCR concentration over the range of 5.0×10^?8–5.0×10^?6 mol·L ^minus;1 with a correlation coefficient of 0.9952 and a detection limit (S/N=3) of 2.6×10^minus;8 mol·L^minus;1. The results indicated that the imprinted polymer films exhibited an excellent selectivity for VCR. The imprinted sensor was successfully used to determine VCR in real samples with recoveries of 90% –120% by using the standard addition method.     

Microstructure and properties of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)‐p‐phenylene diamine (PDA) polyimide/poly(vinylsilsesquioxane) hybrid nanocomposite films

Hybrid nanocomposite films of poly(vinylsilsesquioxane) (PVSSQ) and polyimide (PI) (PI/PVSSQ) were prepared via sol‐gel process from triethoxyvinylsilane (VSSQ) and thermal imidization from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)‐p‐phenylene diamine (PDA) polyamic acid (BPDA‐PDA PAA). We investigated the microstructure; interfacial interaction; and optical, thermal, dielectric, and mechanical properties of the hybrid films. The phase morphologies and degree of surface roughness were evaluated by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. It was found that the surface topography was influenced by the composition of PVSSQ. Hydrogen bonding interactions between polyimide (PI) matrix and PVSSQ domains were proved with FT‐IR spectroscopy. The transparency of the hybrid films was found to be dependent on the PVSSQ content. Incorporating of the PVSSQ in the hybrid composites increased the glass transition temperature of PI. Dielectric constants of the hybrid films were in the range of 2.37–3.59. Properties of the PI films were also significantly enhanced by adding 5–30 wt % of PVSSQ. For comparison, we also prepared the hybrid composites of PI and mixtures of VSSQ and tetraethoxysilane (TEOS) and the PI/silica hybrid composite containing 30 wt % of silica obtained from TEOS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5189–5199, 2004     

Synthesis and properties of ultralow dielectric porous polyimide films containing adamantane

A series of novel ultralow dielectric porous polyimide (PI) films containing adamantane groups was prepared via the thermolysis of polyethylene glycol (PEG) oligomers mixed into PI matrix. Scanning electron microscopy results indicated that the porous PI films showed closed pores with an average diameter of 120 ± 10 nm. Good thermal properties with 5% weight loss temperature of 499 °C in air atmosphere and glass transition temperature in excess of 310 °C were shown for porous PI films. Notably, the ultralow dielectric constant of porous PI films with 1.85 at 1 MHz was obtained and revealed via broadband dielectric spectroscopy. The effects of the chemical structure of the PI matrix and PEG content on the decomposition behavior of PEG and the performance of porous films were investigated. Wide‐angle X‐ray diffraction results indicated that the PI matrix with large d‐spacing generated weaker interactions between the PEG and PI backbone than those of PI matrix with small d‐spacing. As a result, the PEG for the PI matrix with large d‐spacing was completely decomposed. As indicated by the broadband dielectric spectroscopy results, lower dielectric porous PI films were prepared when the PEG contents in the PI matrix increased from 0 to 20 wt %. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 549–559     

Synthesis of polydopamine‐coated graphene–polymer nanocomposites via RAFT polymerization

Graphene‐polymer nanocomposites have significant potential in many applications such as photovoltaic devices, fuel cells, and sensors. Functionalization of graphene is an essential step in the synthesis of uniformly distributed graphene‐polymer nanocomposites, but often results in structural defects in the graphitic sp² carbon framework. To address this issue, we synthesized graphene oxide (GO) by oxidative exfoliation of graphite and then reduced it into graphene via self‐polymerization of dopamine (DA). The simultaneous reduction of GO into graphene, and polymerization and coating of polydopamine (PDA) on the reduced graphene oxide (RGO) surface were confirmed with XRD, UV–Vis, XPS, Raman, TGA, and FTIR. The degree of reduction of GO increased with increasing DA/GO ratio from 1/4 to 4/1 and/or with increasing temperature from room temperature to 60 °C. A RAFT agent, 2‐(dodecylthiocarbonothioylthio)?2‐methylpropionic acid, was linked onto the surface of the PDA/RGO, with a higher equivalence of RAFT agent in the reaction leading to a higher concentration of RAFT sites on the surface. Graphene‐poly(methyl methacrylate), graphene‐poly(tert‐butyl acrylate), and graphene‐poly(N‐isopropylacrylamide) nanocomposites were synthesized via RAFT polymerization, showing their characteristic solubility in several different solvents. This novel synthetic route was found facile and can be readily used for the rational design of graphene‐polymer nanocomposites, promoting their applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3941–3949     

Dispersion of Reduced Graphene Oxide in Multiple Solvents with an Imidazolium‐Modified Hexa‐peri‐hexabenzocoronene

An imidazolium‐modified hexa‐peri‐hexabenzocoronene derivative (HBC‐C₁₁‐MIM[Cl^?]) was designed and synthesized as a stabilizer to fabricate reduced graphene oxide (RGO). The resulting RGO/HBC‐C₁₁‐MIM[Cl^?] hybrid shows excellent dispersivity (5.0 mg mL^?1) and stability in water. RGO/HBC‐C₁₁‐MIM[Cl^?] was comprehensively characterized by using atomic force microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy, thus revealing that one HBC‐C₁₁‐MIM[Cl^?] group can stabilize about 178 carbon atoms on the graphene sheets. The obtained hybrid film exhibits a high conductivity of 286 S m^?1. Furthermore, the HBC‐C₁₁‐MIM[Cl^?]‐modified RGO sheets can be readily dispersed in polar organic solvents upon exchange of the hydrophilic Cl^? ions for hydrophobic bis(trifluoromethylsulfonyl) amide (NTf₂^?) ions.     

Hyperbranched polytriazine grafted reduced graphene oxide and its application

In this article, cyanuric chloride (CC) and hexamethylenediamine (HMD) as raw material, the grafting of hyperbranched polytriazine onto reduced graphene oxide surface (HBP‐RGO) was achieved by the repeated nucleophilic substitution between chlorine groups of CC and amino groups of HMD, respectively. The Fourier transform infrared, X‐ray photoelectron spectroscopic, Raman, transmission electron microscopic, thermogravimetric, and atomic force microscopic analysis showed that HBP‐RGO had been successfully prepared and the HBP had a dendritic structure on the surface of RGO. And then, the HBP‐RGO was added into polystyrene (PS) and the HBP‐RGO/PS composite was prepared by solution mixing. The micro‐morphology, thermal stability, and electrical conductivity of RGO/PS and HBP‐RGO/PS composites were characterized and compared. The scanning electron microscopic analysis showed that the HBP‐RGO can uniformly disperse in PS. Meanwhile, the HBP‐RGO/PS composite showed good thermal stability and electrical conductivity, the percolation threshold of the composites is low as 0.32 vol %. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2132–2140     

Synthesis and Characterization of Aramid Fiber‐Reinforced Polyimide/Carbon Black Composites and Their Use in a Supercapacitor

The aramid fabric (AF )‐reinforced polyimide (PI ) composites filled with carbon black (CB ) were fabricated by means of a thermal imidization and their mechanical, thermal and electrochemical behaviors were comparatively investigated. Experimental results showed that the tensile strength of composite increased with an increase of the CB , meanwhile, the addition of 5 wt% CB and AF increased the tensile modulus to 5682.0 MPa . The superior mechanical properties of the composites were attributed to the good dispersion and effective stress transfer between the polymer and CB , as evidenced by the results from X‐ray diffraction (XRD ) and morphological studies. Besides, the thermal‐nonoxidative stability of PI was significantly improved by the incorporation of CB and AF . Furthermore, the CB /AF /PI composite was employed as the supercapacitor electrode in the 6 mol/L KOH aqueous electrolyte solution, which exhibited a specific capacitance of 510 F•g⁻¹ at 10 mV •s⁻¹. It also exhibited excellent long‐term stability, and the energy density was stable with the increase in the power density. The super performance of the composite electrode is attributed to the synergistic effects of CB particles and organic polymer.