Core-shell particles for design of high-performance polymeric materials with good transparency and toughness

The exfoliated graphene oxides (GOs) prepared via the Hummer’s method were well dispersed in water but re-stacked if drying to a powder form as observed by transmission electron microscope and x-ray diffraction pattern. Hence, they were directly mixed with poly(vinyl alchohol) (PVA) in water to fabricate the PVA/GO nanocomposite films by casting the resulting aqueous solutions and drying. As the nanocomposite films with no less than 5 wt% GO content were subjected to combustion, the char residue could preserve their original film profile acting like an inflammable scaffold. The glassy transition temperature of as-fabricated PVA/GO nanocomposite films barely changed with the content of GO but significantly decreased from ~70 to ~10 °C as environmental relative humidity (RH) was increased from 20 to 80 % due to more moisture adsorption. Therefore, the mechanical behavior of PVA/GO nanocomposite films not only depended on the GO content but also RH, exhibiting from rubbery to glassy status.     

Simultaneously improved actuated performance and mechanical strength of silicone elastomer by reduced graphene oxide encapsulated silicon dioxide

Herein, graphene oxide (GO)-encapsulated silica (SiO₂) hybrids (GO@SiO₂) were prepared via electrostatic self-assembly of the 3-aminopropyltriethoxysilane (APS)-modified SiO₂ and GO. The as-prepared GO@SiO₂ was introduced into polydimethylsiloxane (PDMS) elastomer to simultaneously increase the dielectric constant (k) and mechanical properties of PDMS. Then, the in situ thermal reduction of GO@SiO₂/PDMS composites was conducted at 180°C for 2 h to increase the interfacial polarizability of GO@SiO₂. As a result, the values of k at 1000 Hz are largely improved from 3.2 for PDMS to 13.3 for the reduced GO@SiO₂ (RGO@SiO₂)/PDMS elastomer. Meanwhile, the dielectric loss of the composites remains low (<0.2 at 1000 Hz). More importantly, the actuated strain at low electric field (5 kV/mm) obviously increases from 0.3% for pure PDMS to 2.59% for the composites with 60 phr of RGO@SiO₂, an eightfold increase in the actuated strain. In addition, both the tensile strength and elastic modulus are obviously improved by adding 60 phr of RGO@SiO₂, indicating a good reinforcing effect of RGO@SiO₂ on PDMS. Our goal is to develop a simple and effective way to improve the actuated performance and mechanical strength of the PDMS dielectric elastomer for its wider application.     

Sorption behavior and preliminary pervaporation results of cross-linked polyvinylalcohol and polydimethylsiloxane membranes prepared for the separation of water-ethylacetate mixtures

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 w m thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.     

ZIF-8 Filled Polydimethylsiloxane Membranes for Pervaporative Separation of n-Butanol from Aqueous Solution

ZIF-8-filled polydimethylsiloxane (PDMS) membranes, PDMS/ZIF-8, were prepared by a two-step polymerization process and were used to recover n-butanol from an aqueous solution by pervaporation (PV). Compared with pure PDMS membrane, PDMS/ZIF-8 membranes demonstrated an obviously higher n-butanol permselectivity. As an increase of ZIF-8 content, n-butanol/water selectivity increased initially and then decreased, while the n-butanol and water permeability decreased monotonously. PDMS/ZIF-8 membrane containing 2 wt% ZIF-8, that is, PDMS/ZIF-8-2 showed the highest selectivity. On the other hand, selectivity and permeability for n-butanol and water of PDMS/ZIF-8-2 membrane decreased with the increase of operating temperature. The selectivity and permeability for n-butanol reached 7.1 and 3.28 × 10⁵ barrer, respectively, at 30°C when the feed concentration of n-butanol was 0.96 wt%.     

Mixed Matrix Silicone and Fluorosilicone/Zeolite 4A Membranes for Ethanol Dehydration by Pervaporation

The ability of homogeneous and mixed matrix membranes prepared using standard silicone rubber, poly(dimethylsiloxane) (PDMS), and fluorosilicone rubber, poly(trifluoropropylmethylsiloxane) (PTFPMS), to dehydrate ethanol by pervaporation was evaluated. Although PDMS is generally considered to be the benchmark hydrophobic membrane material in pervaporation, water/ethanol molar permselectivity of a pure PDMS membrane was found to be 0.89 for a feed containing 80/20 w/w ethanol/water at 50°C, indicating a slight selectivity for water. Fluorinated groups in PTFPMS improved the water-ethanol permselectivity to 1.85, but decreased the water permeability from 9.7 × 10^?12 kmol · m/m² · s · kPa in PDMS to 5.1 × 10^?12 kmol · m/m² · s · kPa (29,000 and 15,200 Barrer, respectively). These water permeabilities are attractive, particularly since the rubbery materials should not experience the steep declines in water permeability observed with most standard dehydration membranes as water concentration in the feed decreases. However, the water selectivity is lower than desired for most applications. Particles of hydrophilic zeolite 4A were loaded into both PDMS and PTFPMS matrices in an effort to boost water selectivity and further improve water permeability. Water-ethanol permselectivities as high as 11.5 and water permeabilities as high as 23.2 × 10^?12 kmol · m/m² · s · kPa were observed for the PTFPMS/zeolite 4A mixed matrix membranes?6 times higher than for the unfilled PTFPMS membrane.     

Effect of silver decorated graphene oxide on the PEDOT:PSS-matrix composite films

Silver decorated graphene oxide (GO) was added in poly(3,4-ethylenedioxythiopphene): poly(styrene sulfonate) (PEDOT:PSS) matrix to fabricate composite films, aiming for an improved electrical conductivity. Silver particles were deposited on GO surfaces by reaction with Tollens’ reagent. The composite films reinforced by silver decorated GO showed a sheet resistance of 744 Ω/sq. with 88.9% transparency, which outperformed PEDOT:PSS matrix and GO/PEDOT:PSS composite films. The deposited silver particles were consisted of elementary silver and positively charged silver. The GO surfaces were negatively charged. The distinction of positive domain and negative domain on silver decorated GO surfaces promoted the phase separation of conductive PEDOT molecules and insulting PSS molecules, which contributed to the increase of the electrical conductivity of the composite films. Moreover, the deposition of elementary silver introduced extra electron pathways in the composite films.     

Forward osmosis water desalination: Fabrication of graphene oxide-polyamide/polysulfone thin-film nanocomposite membrane with high water flux and low reverse salt diffusion

This paper investigates the synthesis of graphene oxide (GO)-incorporated polyamide thin-film nanocomposite (TFN) membranes on polysulfone substrate for forward osmosis applications. The GO nanosheets were embedded into polyamide layer using different concentrations (0.05?0.2 wt%). The results represented the alteration of polyamide surface by GO nanosheets and enhancing the surface hydrophilicity by increasing the GO loading. The results showed that the water flux for 0.1 wt% GO embedded nanocomposite (TFN) membrane was 34.7 L/m² h, representing 90% improvement compared to the thin-film composite, while the salt reverse diffusion was reduced up to 39%.     

Effects of graphene oxide on the formation,structure and properties of bionanocomposite films made from wheat gluten with chitosan

Graphene oxide (GO) was combined with wheat gluten (WG) and chitosan (CS) to prepare bionanocomposite films using a casting method. The films were characterized using a variety of techniques, including scanning and transmission electron microscopies, atomic force microscopy, X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, mechanical testing, water swelling, oxygen permeability and contact angle measurements, to determine the effects of GO on the formation, structure and properties of the bionanocomposites. Their formation and properties were found to be dependent on the mixing order of the three components. The added GO was found to strengthen the films, as well as to decrease water absorption and oxygen permeability. These effects were attributed to the good dispersion of GO in the WG/CS matrix enabled by hydrogen bonds. The decreased water absorption could be explained by the increased hydrophobicity. The notable improvement of the properties of the WG/CS films as a result of GO addition makes the films suitable as packaging materials. © 2016 Society of Chemical Industry     

Preparation and properties of β‐phase graphene oxide/PVDF composite films

We report preparation of graphene oxide (GO) from expanded graphite (EG) via a modified Hummers method. GO/PVDF composites films were obtained using solvent N, N‐Dimethylformamide (DMF) and cosolvent comprising deionized water/DMF combination. X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that the main crystal structure of the composite films is β‐phase, and use cosolvent method tends to favor the formation of β‐phase. Scanning electron microscopy (SEM) was used to investigate the microstructure of composite films. Storage modulus and loss modulus were measured by Dynamic mechanical analysis (DMA). Broadband dielectric spectrum tests showed an increase in the dielectric constant of the GO/PVDF composite films with the rising content of GO, and by cosolvent method could improve the dielectric constant while reducing the dielectric loss. Our method that uses GO as an additive and deionized water/DMF as the cosolvent provides a promising and low‐cost pathway to obtain high dielectric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41577.     

Comparative Study of Separation of Acetonitrile from Aqueous Solutions by Pervaporation using Different Membranes

Pervaporation of acetonitrile-water mixtures was carried out using three commercial membranes, viz: polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). The effects of feed concentration and feed temperature on the pervaporation performance, total and partial permeate fluxes, as well as acetonitrile selectivity, were investigated. It was found that increase in temperature yields higher total fluxes and lower selectivity for acetonitrile-water system. Changing concentration of acetonitrile in the range concerned leads to significant effect on total flux and selectivity. PDMS membrane was found to be most selective for acetonitrile separation. The total flux through the membranes was found to be in the order of PTFE > PVDF > PDMS, and the acetonitrile selectivity was found to be in the order of PDMS > PVDF > PTFE. The activation energies of water and acetonitrile associated with the permeation process for the PDMS, PTFE, and PVDF membranes were calculated to be in the ranges of 0.29–0.99, 0.6–0.87, 0.45–2.73 kJ/mol for acetonitrile and 1.23–1.95, 1.37–1.71, 1.16–3.37 kJ/mol for water at different concentrations, respectively.     

Poly (vinyl alcohol)/graphene oxide nanocomposite films and hydrogels prepared by gamma ray

ABSTRACT

Poly (vinyl alcohol)/graphene oxide (PVA/GO) gamma irradiated nanocomposite films and hydrogels were prepared. In composite films, GO was initially irradiated by gamma ray in order to improve interactions between GO and PVA. The film containing 1?wt-% GO was very strong where tensile modulus and tensile yield strength were 45 and 115% higher than those of pure PVA. In the second set of experiments PVA/GO hydrogels were made by irradiating PVA/GO suspensions by gamma ray at various doses. It was an interesting finding that GO increased the gel portion of hydrogels through contribution of H-bonds between PVA and GO. The hydrogels prepared at 20?kGy had remarkable water swelling ratio that reached as high as 20 at water temperature of 80°C. The hydrogel metal ion adsorption capability was tested on Cu²⁺ ions. It was shown that the GO contributed significantly to the adsorption capacity of PVA hydrogels.     

Physicochemical and antibacterial properties of chitosan‐polyvinylpyrrolidone films containing self‐organized graphene oxide nanolayers

Chitosan films have a great potential to be used for wound dressing and food‐packaging applications if their physicochemical properties including water vapor permeability, optical transparency, and hydrophilicity are tailored to practical demands. To address these points, in this study, chitosan (CS) was combined with polyvinylpyrrolidone (PVP) and graphene oxide (GO) nanosheets (with a thickness of ～1 nm and lateral dimensions of few micrometers). Flexible and transparent films with a high antibacterial capacity were prepared by solvent casting methods. By controlling the evaporation rate of the utilized solvent (1 vol % acidic acid in deionized water), self‐organization of GO in the polymer matrix was observed. The addition of PVP to the CS/GO films significantly increased their water vapor permeability and optical transmittance. A blue shift in the optical absorption edge was also noticed. Thermal analysis coupled with Fourier transform infrared spectroscopy suggested that the superior thermal stability of the nanocomposite films was due to the formation of hydrogen bonds between the functional groups of chitosan with those of the graphene oxide. An improved bactericidal capacity of the nanocomposite films against gram‐positive Staphylococcus aureus and gram‐negative Escherichia coli bacteria was also observed. Highly flexible, transparent (opacity of 6.95), and antimicrobial CS/25 vol % PVP/1 wt % GO films were prepared. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43194.     

Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes

This paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F g^?1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F g^?1), electrochemically reduced GO (EC-rGO) (27.6 F g^?1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F g^?1)-based electrodes.     

Quaternized poly (2.6 dimethyl – 1.4 phenylene oxide)/Polysulfone anion exchange membrane reinforced with graphene oxide for methanol alkaline fuel cell application

Composite anion exchange membranes (AEM) based on quaternized poly (phenylene) oxide and polysulfone blend (QPPO/PSF) were successfully fabricated and characterized for methanol alkaline fuel cell application. To make a composite AEM, increasing graphene oxide (GO) wt.% ratios was introduced in the polymer blend. The membrane properties were enhanced by the addition of GO in comparison to the bare QPPO/PSF blend. The addition of GO resulted to a higher ion exchange capacity (IEC) of 3.21 mmol.g^?1 and an ion conductivity increase of up to 63.67 mS.cm^?1 at 80 °C. The QPPO/PSF/2%GO composite membrane reached a peak power density of 112 mW.cm^?2, which is about five (5) times more than the parent QPPO membrane at room temperature. The above results indicate that QPPO/PSF/GO is a good candidate as an anion exchange membrane for alkaline fuel cell application.     

Graphene oxide reinforced chitosan/polyvinylpyrrolidone polymer bio‐nanocomposites

Bio‐nanocomposite films based on chitosan/polyvinylpyrrolidone (CS/PVP) and graphene oxide (GO) were processed using the casting/evaporation technique. It has been found that the three components of bio‐nanocomposites can be easily mixed in controlled conditions enabling the formation of thick films with high quality, smooth surface and good flexibility. Structural and morphological characterizations showed that the GO sheets are well dispersed in the CS/PVP blend forming strong interfacial interactions that provide an enhanced load transfer between polymer chains and GO sheets thus improving their properties. It has been found that the water resistance of the CS/PVP blend is improved, and the hydrolytic degradation is limited by addition of 0.75 and 2 wt % GO. The modulus, strength, elongation and toughness of the bio‐nanocomposites are together increased. Herein, the steps to form new bio‐nanocomposite films have been described, taking the advantage of the combination of CS, PVP and GO to design the aforementioned bio‐nanocomposite films, which allow to have extraordinary properties that would have promising applications as eventual packaging materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41042.     

Preparation and properties of modified graphene oxide incorporated waterborne polyurethane acrylate

In this study, a new modifier (KPG) was prepared by modifying graphene oxide with γ‐glycidoxypropyl trimethoxysilane (KH560) and polydimethylsiloxane (PDMS). KPG was in turn added to aqueous urethane acrylate for the fabrication of waterborne polyurethane polyacrylate emulsion modified with KH560‐PDMS composite (KPG/WPUA). Textural characterizations of the KPG/WPUA coating were achieved via Fourier transform infrared, SEM, TGA and AFM techniques, which revealed that the KPG/WPUA film possessed a smooth surface. The synthesized KPG/WPUA films were tested for mechanical properties, hydrophobicity and acid/water corrosion performance which suggested their highly hydrophobic surface. KPG/WPUA with 0.1% KPG showed a contact angle of 118.35°, 30.35° higher than that of pristine WPUA. The KPG/WPUA film exhibited higher thermal stability, i.e. a 5% weight loss temperature of 305 °C, which was 30 °C higher than that of pristine WPUA film. The Young's modulus and elongation at break of the KPG/WPUA film were 34.1 MPa and 74.88% respectively, which were higher than that of WPUA film. Furthermore, KPG/WPUA films exhibited greater resistance (without obvious blistering and the white spotting phenomenon) to H₂O₂, HCl and water corrosion than pristine WPUA. The superior performance of KPG/WPUA films was attributed to the network chain structure formed upon the introduction of KPG into WPUA. The outstanding performance of KPG/WPUA films in terms of mechanical properties, thermal stability and high resistance to acidic and water corrosion makes them interesting alternative contenders for target applications. © 2019 Society of Chemical Industry     

SORPTION BEHAVIOR AND PRELIMINARY PERVAPORATION RESULTS OF CROSS-LINKED POLYVINYLALCOHOL AND POLYDIMETHYLSILOXANE MEMBRANES PREPARED FOR THE SEPARATION OF WATER-ETHYLACETATE MIXTURES

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 μm thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.     

Properties and structural characterization of oxide starch/chitosan/graphene oxide biodegradable nanocomposites

Novel chitosan (CS)/oxidized starch (OST)/graphene oxide (GO) nanocomposites (COST/GO‐n) films are prepared in a casting and solvent evaporation method. Fourier transform infrared spectroscopy, X‐ray diffractions, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, tensile testing, and moisture uptake are used to study the structure and properties of these nanocomposites. To indicate the effect of carboxyl groups of OST, some results of the properties of CS/starch/GO nanocomposite (CST/GO‐n) were selected for control experimentation. Compared with the control CST/GO‐n series, COST/GO‐n films, which have the same component ration showed higher tensile strength (σ_b) and lower elongation at break (ε_b). Additionally, in the COST/GO‐n series, the σ_b increased with an increase of GO loading. However, higher proportion of GO could result in aggregations of GO nanosheets and deterioration of the film properties. Compared with the COST/GO‐0, the values of σ_b and water resistance of the COST/GO‐4 containing 2.0 wt % of GO were improved by 57.7 and 20.1%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies of cyclic and linear poly(dimethylsiloxanes): 18. Surface pressures of the monolayers in the plateau region

Measurements of the two-dimensional surface pressure π have been made as a function of average area per monomer A at areas too small to support a single monolayer, for films of cyclic and linear poly(dimethylsiloxane) (PDMS) spread on the surface of water at temperatures between 6°C and 31°C. The number-average numbers of monomer units were 10 to 196 for the rings and 10 to 1.2 × 10⁵ for the linear chains. The surface pressures were stable with time for films formed from molecules with more than 20 monomer units. For these films, two plateaux of surface pressure linked by a rounded step were observed for both rings and chains, and the step occurred at the same average area per monomer. However, although the levels of the plateaux were the same for films formed from all linear species, increases in levels of the plateaux with decreasing number of monomer units were observed for cyclic species. The temperature coefficient of the surface pressure was negative in all instances, suggesting that surface entropy is gained upon compression. The unstable films formed from the linear and cyclic decamers were also studied. The former displayed a step in the plateau region, the latter did not appear to. The present findings suggest that cyclic and linear PDMS with more than 20 monomer units collapse by a common mechanism. If the long-standing hypothesis that PDMS collapses by adopting a helical configuration is correct, this implies that rings with as few as 20 repeat units on the average coil into helices.     

Gas transport and mechanical properties of PDMS-TFS/LDPE nanocomposite membranes

This study investigates the effect of trimethylsiloxy fumed silica (TFS) on the mechanical and gas permeation properties of polymer nano-composite membranes. The membranes were produced by coating TFS incorporated polydimethylsiloxane (PDMS) at different loadings (5, 10 and 15 wt.%) on a porous low density polyethylene (LDPE) substrate which was formed by a melt-extrusion/salt leaching technique. The PDMS-TFS/LDPE membranes were characterized by SEM, TGA and DMTA. The results showed that good affinity between the PDMS treated TFS particles and PDMS matrix was obtained leading to improved mechanical and thermal properties. For gas permeation, CH₄ and C₃H₈ at different upstream pressure (50 to 80 psig) and temperature (27 to 55 °C) were investigated. The results showed that the C₃H₈/CH₄ ideal selectivity (17.6) and C₃H₈ permeability (1.89?×?10⁴ Barrer) through 10 wt.% TFS loaded membranes (PDMS-TFS10%/LDPE) were 41 and 14% higher than the neat membranes (PDMS-TFS0%/LDPE), respectively. The permeation results also indicate that the performance stability under the conditions investigated makes PDMS-TFS/LDPE membranes interesting for industrial applications.