Showing papers by "Ilhan A. Aksay published in 2008"

Raman Spectra of Graphite Oxide and Functionalized Graphene Sheets

Abstract: We investigate Raman spectra of graphite oxide and functionalized graphene sheets with epoxy and hydroxyl groups and Stone−Wales and 5−8−5 defects by first-principles calculations to interpret our experimental results. Only the alternating pattern of single−double carbon bonds within the sp2 carbon ribbons provides a satisfactory explanation for the experimentally observed blue shift of the G band of the Raman spectra relative to graphite. To obtain these single−double bonds, it is necessary to have sp3 carbons on the edges of a zigzag carbon ribbon.

Functionalized graphene sheets for polymer nanocomposites

Abstract: Polymer-based composites were heralded in the 1960s as a new paradigm for materials. By dispersing strong, highly stiff fibres in a polymer matrix, high-performance lightweight composites could be developed and tailored to individual applications. Today we stand at a similar threshold in the realm of polymer nanocomposites with the promise of strong, durable, multifunctional materials with low nanofiller content. However, the cost of nanoparticles, their availability and the challenges that remain to achieve good dispersion pose significant obstacles to these goals. Here, we report the creation of polymer nanocomposites with functionalized graphene sheets, which overcome these obstacles and provide superb polymer-particle interactions. An unprecedented shift in glass transition temperature of over 40 degrees C is obtained for poly(acrylonitrile) at 1 wt% functionalized graphene sheet, and with only 0.05 wt% functionalized graphene sheet in poly(methyl methacrylate) there is an improvement of nearly 30 degrees C. Modulus, ultimate strength and thermal stability follow a similar trend, with values for functionalized graphene sheet- poly(methyl methacrylate) rivaling those for single-walled carbon nanotube-poly(methyl methacrylate) composites.

Bending properties of single functionalized graphene sheets probed by atomic force microscopy.

Abstract: We probe the bending characteristics of functionalized graphene sheets with the tip of an atomic force microscope. Individual sheets are transformed from a flat into a folded configuration. Sheets can be reversibly folded and unfolded multiple times, and the folding always occurs at the same location. This observation suggests that the folding and bending behavior of the sheets is dominated by pre-existing kink (or even fault) lines consisting of defects and/or functional groups.

Processing and Microstructural Characterization of B4C-AI Cermets

Abstract: Des etudes de mouillage et de thermodynamique des reactions ont ete utilisees pour evaluer des cermets, aluminium-carbure de bore. Le phenomene de mouillage et les reactions interfaciales sont caracterises par des techniques «macroechelle» et «microechelle». Etude des microstructures par microscopie electronique a balayage, diffraction RX, metallographie et microsonde electronique

Electrohydrodynamic Flow and Colloidal Patterning near Inhomogeneities on Electrodes

Abstract: Current density inhomogeneities on electrodes (of physical, chemical, or optical origin) induce long-range electrohydrodynamic fluid motion directed toward the regions of higher current density. Here, we analyze the flow and its implications for the orderly arrangement of colloidal particles as effected by this flow on patterned electrodes. A scaling analysis indicates that the flow velocity is proportional to the product of the applied voltage and the difference in current density between adjacent regions on the electrode. Exact analytical solutions for the streamlines are derived for the case of a spatially periodic perturbation in current density along the electrode. Particularly simple asymptotic expressions are obtained in the limits of thin double layers and either large or small perturbation wavelengths. Calculations of the streamlines are in good agreement with particle velocimetry experiments near a mechanically generated inhomogeneity (a "scratch") that generates a current density larger than that of the unmodified electrode. We demonstrate that proper placement of scratches on an electrode yields desired patterns of colloidal particles.

Collodial cluster arrays by electrohydrodynamic printing.

Abstract: A "stable" electrohydrodynamic jet is used to print arrays of colloidal suspensions on hydrophobic surfaces. Printed lines break up into sessile drops, and capillary forces guide the self-assembly of colloidal particles during the evaporation of the liquid, resulting in arrays of colloidal single particles or particle clusters depending on the concentration of the suspensions. The clusters differ from those formed in the absence of a substrate when the number of particles is larger than three. Multiple structures are found for the same number of particles.

Inhibition and promotion of copper corrosion by CTAB in a microreactor system.

Abstract: We report on an optical microscopy technique for the analysis of corrosion kinetics of metal thin films in microreactor systems and use it to study the role of cetyltrimethylammonium bromide surfactant as a corrosion inhibitor in a copper−gold galvanic coplanar microsystem. A minimum in the dissolution rate of copper is observed when the surfactant concentration is ∼0.8 mM. To explain why the inhibitory role of the surfactant does not extend to higher concentrations, we use zero resistance ammetry with separated half cells and show that while the surfactant inhibits cathodic reactions on gold, it also promotes the corrosion of copper because of the catalytic action of bromide counterions. These two competing processes lead to the observed minimum in the dissolution rate.

Enhanced Stability of Electrohydrodynamic Jets through Gas Ionization

Abstract: Theoretical predictions of the nonaxisymmetric instability growth rate of an electrohydrodynamic jet based on the measured total current overestimate experimental values. We show that this apparent discrepancy is the result of gas ionization in the surrounding gas and its effect on the surface charge density of the jet. As a result of gas ionization, a sudden drop in the instability growth rate occurs below a critical electrode separation, yielding highly stable jets that can be used for nano- to microscale printing.

Electrospray painted article containing thermally exfoliated graphite oxide and method for their manufacture

Abstract: A painted polymer part containing a conductive polymer composition containing at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g, wherein the painted polymer part has been electrospray painted.

Orientational Order of Molecular Assemblies on Rough Surfaces

Abstract: Using atomic force microscopy, we show that previous observations on the orientational order of micelles on atomically smooth crystals with directions dictated by the crystal symmetry is only valid for the case of perfectly smooth crystals. On rough surfaces, orientations are independent of the lattice symmetry and the observed directions can be explained by considering the guiding influence of topographic surface features.

Bridged graphite oxide materials

Abstract: Bridged graphite oxide material comprising graphite sheets bridged by at least one diamine bridging group. The bridged graphite oxide material may be incorporated in polymer composites or used in adsorption media.

Linear colloidal crystal arrays by electrohydrodynamic printing

Abstract: We use electrohydrodynamic jets of colloidal suspensions to produce arrays of colloidal crystalline stripes on surfaces. A critical factor in maintaining a stable jet is the distance of separation between the nozzle and the surface. Colloidal crystalline stripes are produced as two wetting lines of the deployed suspension merge during drying. To ensure that the two wetting lines merge, the “deployed-line-width” to “particle size” ratio is kept below a critical value so that the capillary forces overcome the frictional forces between the particles and the substrate.

Tire containing thermally exfoliated graphite oxide

Abstract: A tire, tire lining or inner tube, containing a polymer composite, made of at least one rubber and/or at least one elastomer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.

Polymerization method for formation of thermally exfoliated graphite oxide containing polymer

Abstract: A process for polymerization of at least one monomer including polymerizing the at least one monomer in the presence of a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m 2 /g to 2600 m 2 /g.

Tip-Induced Orientational Order of Surfactant Micelles on Gold

Abstract: Using liquid-cell atomic force microscopy, we investigate aqueous solutions of alkyltrimethylammonium halide surfactants at the Au(111) surface. The long, micellar surfactant surface aggregates cover the gold surface completely and exhibit two types of orientational order for chloride and bromide counterions, respectively. We observe lateral forces perpendicular to the scanning direction, which we explain by anisotropic friction between the probe and the oriented micelles. Conversely, we show that these friction forces can be employed to modify the spatial conformation of the micellar adlayer. Where previous methods have failed to provide control over the orientation down to the level of individual micelles, we use this technique to achieve a very high degree of order over more than 100 micelle diameters.

Conductive ink containing thermally exfoliated graphite oxide and method a conductive circuit using the same

Abstract: A conductive ink containing a conductive polymer, wherein the conductive polymer contains at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m 2 /g to 2600 m 2 /g, and it use in a method for making a conductive circuit.

Gas storage cylinder formed from a composition containing thermally exfoliated graphite

Abstract: A gas storage cylinder or gas storage cylinder liner, formed from a polymer composite, containing at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.

Separation medium containing thermally exfoliated graphite oxide

Abstract: A separation medium, such as a chromatography filling or packing, containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g, wherein the thermally exfoliated graphite oxide has a surface that has been at least partially functionalized.

Supercapacitor and battery electrode containing thermally exfoliated graphite oxide

Abstract: A supercapacitor or battery electrode containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m 2 /g to 2600 m 2 /g.

Emulsifier containing thermally exfoliated graphite oxide

Abstract: An emulsifier containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g

Wire coating containing thermally exfoliated graphite oxide

Abstract: A wire coating containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.

Automotive body panel containing thermally exfoliated graphite oxide

Abstract: An automotive body panel containing a polymer composite formed of at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m 2 /g to 2600 m 2 /g.

Packaging material and flexible medical tubing containing thermally exfoliated graphite oxide

Abstract: A packaging material or flexible medical tubing containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.