Facile Synthesis and Characterization of Few-Layer Multifunctional Graphene from Sustainable Precursors by Controlled Pyrolysis, Understanding of the Graphitization Pathway, and Its Potential Application in Polymer Nanocomposites.

The key feature of the present work is the dexterous utilization of an apparently destructive process, pyrolysis, for the synthesis of the most esteemed nanomaterial, graphene. This work is an attempt to synthesize graphene from nonconventional sources such as tannic acid, alginic acid, and green tea by a controlled pyrolysis technique. The precursors used in this work are not petroleum-derived and hence are green. A set of pyrolysis experiments was carried out at different temperatures, followed by a thorough step-by-step analysis of the product morphology, enabling the optimization of the graphitization conditions. A time-dependent morphological analysis was also carried out along with isothermal thermogravimetric studies to optimize the ideal pyrolysis time for graphitization. The specific capacitance of the graphene obtained from alginic acid was 315 F/g, which makes it fairly suitable for application as green supercapacitors. The same graphene was also used to fabricate a rubber-latex-based flexible supercapacitor film with 137 F/g specific capacitance. The graphene and graphene-based latex film exhibited room-temperature magnetic hysteresis, indicating their ferromagnetic nature, which also supports their spintronic applications.

Controlled Methodology for Development of a Polydimethylsiloxane-Polytetrafluoroethylene-Based Composite for Enhanced Chemical Resistance: A Structure-Property Relationship Study.

Polydimethylsiloxane (PDMS) polymers are highly appreciated materials that are broadly applied in several industries, from baby bottle nipples to rockets. Momentive researchers are continuously working to understand and expand the scope of PDMS-based materials. Fluorofunctional PDMS has helped the world to apply in specialty applications. Efforts are taken to develop such siloxane-fluoropolymer composite materials with good thermal, solvent, and chemical resistance performances. We leveraged inherently flexible PDMS as the model matrix, whereas polytetrafluoroethylene (PTFE) was used as the additive to impart the functional benefits, offering great value in comparison to the individual polymers. The composites were made at three different mixing temperatures, that is, 0-35 °C, and different loadings of PTFE, that is, 0.5-8% (w/w), were selected as the model condition. A strong dependency of the mixing temperature against the performance attributes of the developed composites was noted. Mechanical and thermal stability of the composites were evaluated along with optical properties. X-ray diffraction demonstrated the change in the crystallite size of the PTFE particles as a function of processing temperature. Compared to the phase II crystallite structure of the PTFE, the fibrils formed in phase IV imparted a better reinforcing capability toward the PDMS matrix. A synergistic balance between higher filler loading and mechanical properties of the composite can be achieved by doping the formulation with short-chain curable PDMS, with 238% increment of tensile strength at 8 wt % PTFE loading when compared to the control sample. The learning was extended to check the applicability of doping such PTFE powder in commercial liquid silicone rubber (LSR). In the window of study, the formulated LSR demonstrated improved mechanical properties with additional functional benefits like resistance toward engine oil and other chemical solvents.

Selective Orientation of Needlelike Sepiolite Nanoclay in Polymer Blend for Controlled Properties.

Sepiolite nanoclay needles have been selectively localized either in the natural rubber (NR) phase or in the carboxylated nitrile rubber (XNBR) phase of the XNBR/NR (50/50) blend prepared by the solution casting method. In a systematic manner, the role of the difference value between the interaction parameter of individual blend components (NR or XNBR)/solvent and the interaction parameter of sepiolite nanoclay/solvent in selectively localizing the sepiolite nanoclay to the NR phase or the XNBR phase of the XNBR/NR (50/50) blend has been explored. A higher percentage of sepiolite nanoclay resides in the dispersed NR phase when the difference value between the interaction parameter of NR/solvent and the interaction parameter of sepiolite nanoclay/solvent is lower than the difference value between the interaction parameter of XNBR/solvent and the interaction parameter of sepiolite nanoclay/solvent. On the other hand, a higher percentage of sepiolite nanoclay resides in the continuous XNBR phase when the difference value between the interaction parameter of XNBR/solvent and the interaction parameter of sepiolite nanoclay/solvent is lower than the difference value between the interaction parameter of NR/solvent and the interaction parameter of sepiolite nanoclay/solvent. It has been shown that by judiciously choosing different solvent combinations to prepare the blend and to disperse nanoclay, it is possible to fine-tune the difference value between the interaction parameter of individual blend components (NR or XNBR)/solvent and the interaction parameter of sepiolite nanoclay/solvent and dictate the selective localization of sepiolite nanoclay to the NR phase or the XNBR phase of XNBR/NR (50/50) blend. This study shows that it is possible to generate a rubber blend with controlled properties by selectively localizing needlelike sepiolite nanoclay in the dispersed phase or the continuous phase of the rubber blend prepared by the solution casting method.

Impeded repair of abasic site damaged lesions in DNA adsorbed over functionalized multiwalled carbon nanotube and graphene oxide.

The processing of abasic site DNA damage lesions in extracellular DNA in the presence of engineered carbon nanomaterials (CNMs) is demonstrated. The efficacy of the apurinic-apyrimidinic endonuclease 1 (APE1) in the cleavage of abasic site lesions in the presence of carboxylated multi-walled carbon nanotubes (MWCNT-COOH) and graphene oxide (GO) are compared. The CNMs were found to perturb the incision activity of APE1. The reason for such perturbation process was anticipated to take place either by the non-specific adsorption of APE1 over the free surface of the CNMs or steric hindrance offered by the CNM-DNA complex. Accordingly, bovine serum albumin (BSA) was selectively utilized to block the free surface of the CNM-DNA hybrid material. Further treatment of the CNM-DNA-BSA complex with APE1 resulted in a marginal increase in APE1 efficiency. This indicates that APE1 in solution is unable to process the abasic sites on DNA adsorbed over the CNMs. However, the cleavage activity of APE1 was restored in the presence of non-ionic surfactant (Tween 20) that inhibits adsorption of the DNA on the surface of the CNMs. The conformational deformation of the DNA, along with steric hindrance induced by the CNMs resulted in the inhibition of abasic site DNA repair by APE1. Moreover, appreciable changes in the secondary structure of APE1 adsorbed over the CNMs were observed that contribute further to the repair refractivity of the abasic sites. From a toxicological viewpoint, these findings can be extended to the study of the effect of engineered nanoparticles in the intracellular DNA repair process.

Graphene Nanocomposites with High Molecular Weight Poly(ε-caprolactone) Grafts: Controlled Synthesis and Accelerated Crystallization.

Grafting of high molecular weight polymers to graphitic nanoplatelets is a critical step toward the development of high performance graphene nanocomposites. However, designing such a grafting route has remained a major impediment. Herein, we report a "grafting to" synthetic pathway by which high molecular weight polymer, poly(ε-caprolactone) (PCL), is tethered, at high grafting density, to highly anisotropic graphitic nanoplatelets. The efficacy of this tethering route and the resultant structural arrangements within the composite are confirmed by neutron and X-ray scattering measurements in the melt and solution phase. In the semicrystalline state, X-ray analysis indicates that chain tethering onto the graphitic nanoplatelets results in conformational changes of the polymer chains, which enhance the nucleation process and aid formation of PCL crystallites. This is corroborated by the superior thermal properties of the composite, manifested in accelerated crystallization kinetics and a significant increase in the thermal degradation temperature. In principle, this synthesis route can be extended to a variety of high molecular weight polymers, which can open new avenues to solution-based processing of graphitic nanomaterials and the fabrication of complex 3D patterned graphitic nanocomposites.

DNA-melamine hybrid molecules: from self-assembly to nanostructures.

Single-stranded DNA-melamine hybrid molecular building blocks were synthesized using a phosphoramidation cross-coupling reaction with a zero linker approach. The self-assembly of the DNA-organic hybrid molecules was achieved by DNA hybridization. Following self-assembly, two distinct types of nanostructures in the form of linear chains and network arrays were observed. The morphology of the self-assembled nanostructures was found to depend on the number of DNA strands that were attached to a single melamine molecule.

Conducting instant adhesives by grafting of silane polymer onto expanded graphite.

A "grafting to" methodology for the attachment of a silane based polymer (SG) onto functionalized graphitic platelets is demonstrated. The siloxy end groups of the modifier were further cross-linked without addition of any external curative. These sterically stabilized nanoplatelets with a high grafting density ensured complete screening of the attractive interparticle interactions. As a result, a better dispersion of platelets was observed compared to the physically mixed platelets in the polymer matrix (SUG). The larger size of the polymer tethered graphitic particles and the greater extent of heat liberated due to grafting resulted in a higher enthalpic contribution in the case of SG compared to SUG. This makes the formation of SG thermodynamically more favorable compared to SUG. Presence of a hierarchical spatial arrangement with a good dispersion of graphitic platelets was observed within the siloxane matrix in the case of SG compared to SUG. The nanoparticle tethered composite generated exhibited an "instant" conducting adhesive behavior. The adhesive properties of the SG were found to be increased due to grafting of graphitic platelets when compared with the neat polymer. Further, SG exhibited a conductive character whereas the neat polymer and SUG demonstrated an insulating character.

Processing of abasic site damaged lesions by APE1 enzyme on DNA adsorbed over normal and organomodified clay.

The efficiency of the apurinic/apyrimidinic endonuclease (APE1) DNA repair enzyme in the processing of abasic site DNA damage lesions at precise location in DNA oligomer duplexes that are adsorbed on clay surfaces was evaluated. Three different forms of clay namely montmorillonite, quaternary ammonium salt modified montmorillonite and its boiled counterpart i.e. partially devoid of organic moiety were used for a comparative study of adsorption, desorption and DNA repair efficiency on their surfaces. The interaction between the DNA and the clay was analysed by X-ray diffraction, Atomic force microscopy, UV-Vis spectroscopy and Infrared spectroscopy. The abasic site cleavage efficiency of APE1 enzyme was quantitatively evaluated by polyacrylamide gel electrophoresis. Apart from the difference in the DNA adsorption or desorption capacity of the various forms of clay, substantial variation in the repair efficiency of abasic sites initiated by the APE1 enzyme on the clay surfaces was observed. The incision efficiency of APE1 enzyme at abasic sites was found to be greatly diminished, when the DNA was adsorbed over organomodified montmorillonite. The reduced repair activity indicates an important role of the pendant surfactant groups on the clay surfaces in directing APE1 mediated cleavage of abasic site DNA damage lesions.

Stress generation and tailoring of electronic properties of expanded graphite by click chemistry.

The generation of stress in expanded graphite (E-GPT) due to covalent attachment of bulky side groups connected via a hetero atom is reported. Specifically, E-GPT is modified at different levels of grafting using "click" chemistry to graft 1-ethynyl-4-fluoro benzene onto graphene sheets via a triazole ring. In the range of grafting densitites examined, Raman spectroscopy indicates that the stress generated in graphene is linearly dependent on the extent of grafting. The functionalized graphene platelets with 6% functionalization transform from semi-metal behavior of the pristine material to semi-conductor behavior and indicates the ability of functionalization to change optical and electronic properties of graphene platelets similar to the deposition of thin layers of top gate oxides onto graphene.

Synthesis and characterization of a biocompatible monotyrosine-based polymer and its interaction with DNA.

A novel tyrosine-based copolymer containing l-tyrosine (Tyr) and diglycidylether of bisphenol A(DGEBA) was synthesized and studied for its interaction with DNA for potential applications in biological systems. The synthesis of the polymer was optimized by varying monomer ratios using 4-(dimethylamino)pyridine (DMAP) as a catalyst to yield polymers with a Mw of 7500-8000. Further characterization by FTIR, NMR and thermal analysis supported the formation of the monotyrosine-DGEBA polymer. The interaction of the 1 : 1 DGEBA-tyrosine copolymer with DNA was investigated by gel electrophoresis, thermal melting, and fluorescence spectroscopy in ratios ranging from 0.5 : 1 to 12 : 1 polymer-DNA (w/w). The copolymer was seen to lend stability to the DNA without damaging it and demonstrated endonuclease resistivity that is conducive for biological applications. Scanning electron microscopy, dynamic light scattering and zeta potential studies of the polymer-DNA complex also established that the polymer is capable of encapsulating DNA leading to the formation of the DNA-polymer polyplex nano-assembly. The potential of the polymer for biological applications was further reinstated by its non-cytotoxicity.

Polyaniline-carbon nanofiber composite by a chemical grafting approach and its supercapacitor application.

Unlike conventional routes by van der Waals forces, a facile and novel approach using covalent bonding is established in the present work to synthesize polyaniline (PANI)-grafted carbon nanofiber (CNF) composites as promising supercapacitors. For this purpose, toluenediisocyanate was initially functionalized to carboxylated CNF via amidation followed by reaction with excess aniline to form a urea derivative and residual aniline, which was subsequently polymerized and grafted with a urea derivative. Amidation of CNF (TCNF) and, consequently, the grafting of PANI on TCNF were verified by IR, Raman, 1H NMR, X-ray photoelectron, and UV-visible spectroscopic methods, X-ray diffraction, and thermogravimetric analysis. Morphological analysis revealed uniform distribution of PANI on the surface of TCNF, indicating strong interaction between them. Electrochemical tests of the composite containing 6 wt % TCNF demonstrated efficient capacitance of ∼557 F g(-1) with a capacity retention of 86% of its initial capacitance even after 2000 charge-discharge cycles at a current density of 0.3 A g(-1), suggesting its superiority compared to the materials formed by van der Waals forces. The remarkably enhanced electrochemical performance showed the importance of the phenyl-substituted amide linkage in the development of a π-conjugated structure, which facilitated charge transfer and, consequently, made it attractive for efficient supercapacitors.

Bionanowhiskers from jute: preparation and characterization.

Bionanowhiskers were extracted from jute by acid hydrolysis. At first cellulose microfibrils were formed by alkali treatment. Addition of an acid to the microfibrils triggered the formation of cellulose nanowhiskers. These were characterized by using different techniques viz. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetry (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). In the FTIR study, absence of peak at 1738 cm(-1) indicated removal of hemicellulose. The rod like morphology of the nanowhiskers (length - 550±100 nm, width - 77±30 nm) was observed after 1h of acid hydrolysis, whereas further increase in time resulted in triangular shape morphology. Acid hydrolysis increased crystallinity, but decreased the temperature corresponding to major degradation (T(max)) and onset of degradation (T(i)). These bionanowhiskers might be useful as reinforcing element in nanocomposites.

Effect of various nanofillers on thermal stability and degradation kinetics of polymer nanocomposites.

Structure of nanofillers and their subsequent interaction with a polymer is very important in determining thermal stability of polymer nanocomposite. In this paper, we tried to correlate structure of various 0, 1 and 2 dimensional nanofillers with the thermal stability of hydrogenated nitrile butadiene rubber (HNBR) nanocomposites. Organically modified and unmodified layered silicates such as montmorillonite (Cloisite Na+, Cloisite 30B and Cloisite 15A), rod-like fibrous filler (sepiolite) and spherical nanoparticles (nanosilica) were chosen for this purpose. A significant improvement in thermal stability (obtained by thermogravimeric analysis and differential scanning calorimetry) was observed for silica-filled nanocomposites. However, the activation energy of the nanocomposites calculated by different kinetic methods (both non-isothermal and isothermal methods) was found to be significantly high for sepiolite, 30B and silica-filled nanocomposites. The results were explained with the help of structure of the nanofillers, their interaction with the elastomer and the subsequent dispersion, as measured by X-ray diffraction, transmission electron microscopy and atomic force microscopy. From these analyses it was concluded that organically modified montmorillonite, sepiolite and nanosilica increase the thermal stability of the nanocomposite to a great extent due to the interaction of the reactive groups on the surface of these fillers with the polymer and high thermal stability of these inorganic fillers. Finally, degradation mechanism of HNBR in presence of the nanofillers at severe operating temperatures was investigated with the help of FTIR spectroscopy.

Nanostructured magnesium oxide as cure activator for polychloroprene rubber.

The aim of this research was to synthesize magnesium oxide nanoparticles and to use them as cure activator for polychloroprene rubber (CR). The effects of counterions of magnesium salts on the homogeneous phase precipitation reaction to control size, monodispersity, crystallinity, and morphology of Mg(OH)2 nanoparticles were also investigated. Magnesium oxide nanoparticles were synthesized by optimizing the calcination temperature of Mg(OH)2 nanoparticles. Finally, the MgO nanoparticles were dispersed in polychloroprene rubber (CR) solution along with zinc oxide (ZnO) powder. The influence of MgO nanoparticles on the mechanical, dynamic mechanical and thermal properties of the resulting nanocomposites was quantified. The modulus and strength of ZnO-cured polychloroprene rubber with 4% MgO nanoparticles appeared to be superior to those with ZnO particles or ZnO with rubber grade MgO particles. These composites were further characterized by transmission electron microscopy and infrared spectroscopy in order to understand the morphology of the resulting system and the load transfer mechanism.

Effect of the microstructure of a hyperbranched polymer and nanoclay loading on the morphology and properties of novel polyurethane nanocomposites.

Novel polyurethane nanocomposites based on toluene diisocyanate, poly(propylene glycol), various hyperbranched polymers (HBPs), and layered silicate were synthesized with the aim of determining the effect of the layered silicate loading and the functionality of HBP on the structure and properties of polyurethane nanocomposites. The microstructure of the nanocomposites was investigated by X-ray diffraction analysis and high-resolution transmission electron microscopy. It was found that exfoliated morphology and good dispersion were obtained up to 8 phr clay loading for all of the nanocomposites. approximately 100% increment in tensile strength, approximately 2-fold increase in the lap shear strength, approximately 200% increment in the peel strength, and 120% increment in the storage modulus along with a dramatic improvement in thermal stability were observed with the addition of 8 phr clay, over the pristine polyurethane. The higher the level of functionality of the HBP, the higher is the property enhancement. These properties were correlated with the state of dispersion of the clay platelets in the polyurethane matrix, the structure of the matrix, and clay-polymer interaction.

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate-Carbon Nanofiller Nanocomposites.

A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers-expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller.

Influence of Nanogels on Mechanical, Dynamic Mechanical, and Thermal Properties of Elastomers.

Use of sulfur crosslinked nanogels to improve various properties of virgin elastomers was investigated for the first time. Natural rubber (NR) and styrene butadiene rubber (SBR) nanogels were prepared by prevulcanization of the respective rubber lattices. These nanogels were characterized by dynamic light scattering, atomic force microscopy (AFM), solvent swelling, mechanical, and dynamic mechanical property measurements. Intermixing of gel and matrix at various ratios was carried out. Addition of NR gels greatly improved the green strength of SBR, whereas presence of SBR nanogels induced greater thermal stability in NR. For example, addition of 16 phr of NR gel increased the maximum tensile stress value of neat SBR by more than 48%. Noticeable increase in glass transition temperature of the gel filled systems was also observed. Morphology of these gel filled elastomers was studied by a combination of energy dispersive X-ray mapping, transmission electron microscopy, and AFM techniques. Particulate filler composite reinforcement models were used to understand the reinforcement mechanism of these nanogels. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11671-009-9262-5) contains supplementary material, which is available to authorized users.

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites.

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.

Effect of silica nanoparticles on reinforcement of poly(phenylene ether) based thermoplastic elastomer.

Reinforcement of a novel poly(phenylene ether) (PPE) based thermoplastic elastomer (TPE), i.e., styrene-ethylene-butylene-styrene (SEBS)/ethylene vinyl acetate (EVA) and PPE-polystyrene (PS), was studied to develop a reinforced thermoplastic elastomer or thermoplastic vulcanizate (TPV). An effort was made to reinforce selectively the elastomeric dispersed phase of EVA by silica nanoparticles and silica sol-gel precursors, like alkoxy orthosilanes, using twin-screw extrusion and injection molding processes. Improvement of tensile strength and percent elongation at break was observed both with silica nanoparticles and tetraethoxy orthosilane (TEOS). Addition of TEOS transformed the dispersed EVA lamellar morphology into semispherical domains as a consequence of possible crosslinking. Soxhlet extraction was done on the silica and TEOS reinforced materials. The insoluble residues collected from both the silica and TEOS reinforced samples were analyzed in detail using both morphological and spectroscopic studies. This extensive study also provided an in-depth conceptual understanding of the PPE based TPE behavior upon reinforcement with silica nanoparticles and silica sol-gel precursors and the effect of reinforcement on recycling behavior.

Fabrication and properties of ethylene vinyl acetate-carbon nanofiber nanocomposites.

Carbon nanofiber (CNF) is one of the stiffest materials produced commercially, having excellent mechanical, electrical, and thermal properties. The reinforcement of rubbery matrices by CNFs was studied in the case of ethylene vinyl acetate (EVA). The tensile strength was greatly (61%) increased, even for very low fiber content (i.e., 1.0 wt.%). The surface modification of the fiber by high energy electron beam and gamma irradiation led to better dispersion in the rubber matrix. This in turn gave rise to further improvements in mechanical and dynamic mechanical properties of EVA. The thermal conductivity also exhibited improvements from that of the neat elastomer, although thermal stability of the nanocomposites was not significantly altered by the functionalization of CNFs. Various results were well supported by the morphological analysis of the nanocomposites.