Publications by Year: 2012

2012
Prud'homme, R. K. ; Aksay, I. A. ; Herrera-Alonso, M. Separation medium containing thermally exfoliated graphite oxide, 2012.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.
Prud'homme, R. K. ; O'Neil, C. ; Ozbas, B. ; Aksay, I. A. ; Register, R. ; Adamson, D. Functional graphene-polymer nanocomposites for gas barrier applications, 2012.Abstract
A gas diffusion barrier contains a polymer matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as determined by X-ray diffraction.
Prud'homme, R. K. ; Aksay, I. A. Gas storage cylinder formed from a composition containing thermally exfoliated graphite, 2012.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.
Aksay, I. A. ; Yeh, T. C. - H. ; Saville, D. A. Supercapacitor and battery electrode containing thermally exfoliated graphite oxide, 2012.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 m2/g to 2600 m2/g.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Wang, D. ; Yang, Z. Nanocomposite of graphene and metal oxide materials, 2012.Abstract
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10C.
Punckt, C. ; Jan, L. ; Jiang, P. ; Frewen, T. A. ; Saville, D. A. ; Kevrekidis, I. G. ; Aksay, I. A. Autonomous colloidal crystallization in a galvanic microreactor. Journal of Applied Physics 2012, 112.Abstract
We report on a technique that utilizes an array of galvanic microreactors to guide the assembly of two-dimensional colloidal crystals with spatial and orientational order. Our system is comprised of an array of copper and gold electrodes in a coplanar arrangement, immersed in a dilute hydrochloric acid solution in which colloidal micro-spheres of polystyrene and silica are suspended. Under optimized conditions, two-dimensional colloidal crystals form at the anodic copper with patterns and crystal orientation governed by the electrode geometry. After the aggregation process, the colloidal particles are cemented to the substrate by co-deposition of reaction products. As we vary the electrode geometry, the dissolution rate of the copper electrodes is altered. This way, we control the colloidal motion as well as the degree of reaction product formation. We show that particle motion is governed by a combination of electrokinetic effects acting directly on the colloidal particles and bulk electrolyte flow generated at the copper-gold interface. (C) 2012 American Institute of Physics.
Bozlar, M. ; Punckt, C. ; Korkut, S. ; Zhu, J. ; Foo, C. C. ; Suo, Z. G. ; Aksay, I. A. Dielectric elastomer actuators with elastomeric electrodes. Applied Physics Letters 2012, 101.Abstract
For many applications of dielectric elastomer actuators, it is desirable to replace the carbon-grease electrodes with stretchable, solid-state electrodes. Here, we attach thin layers of a conducting silicone elastomer to prestrained films of an acrylic dielectric elastomer and achieve voltage-actuated areal strains over 70%. The influence of the stiffness of the electrodes and the prestrain of the dielectric films is studied experimentally and theoretically. (C) 2012 American Institute of Physics.
Liu, L. M. ; Car, R. ; Selloni, A. ; Dabbs, D. M. ; Aksay, I. A. ; Yetter, R. A. Enhanced Thermal Decomposition of Nitromethane on Functionalized Graphene Sheets: Ab Initio Molecular Dynamics Simulations. Journal of the American Chemical Society 2012, 134, 19011-19016.Abstract
The burning rate of the monopropellant nitromethane (NM) has been observed to increase by adding and dispersing small amounts of functionalized graphene sheets (FGSs) in liquid NM. Until now, no plausible mechanisms for FGSs acting as combustion catalysts have been presented. Here, we report ab initio molecular dynamics simulations showing that carbon vacancy defects within the plane of the FGSs, fimctionalized with oxygen-containing groups, greatly accelerate the thermal decomposition of NM and its derivatives. This occurs through reaction pathways involving the exchange of protons or oxygens between the oxygen-containing functional groups and NM and its derivatives. FGS initiates and promotes the decomposition of the monopropellant and its derivatives, ultimately forming H2O, CO2, and N-2. Concomitantly, oxygen-containing functional groups on the FGSs are consumed and regenerated without significantly changing the FGSs in accordance with experiments indicating that the FGSs are not consumed during combustion.
Roy-Mayhew, J. D. ; Boschloo, G. ; Hagfeldt, A. ; Aksay, I. A. Functionalized Graphene Sheets as a Versatile Replacement for Platinum in Dye-Sensitized Solar Cells. ACS Applied Materials & Interfaces 2012, 4 2794-2800.Abstract
Several techniques for fabricating functionalized graphene sheet (FGS) electrodes were tested for catalytic performance in dye-sensitized solar cells (DSSCs). By using ethyl cellulose as a sacrificial binder, and partially thermolyzing it, we were able to create electrodes which exhibited lower effective charge transfer resistance (<1 Omega cm(2)) than the thermally decomposed chloroplatinic acid electrodes traditionally used. This performance was achieved not only for the triiodide/iodide redox couple, but also for the two other major redox mediators used in DSSCs, based on cobalt and sulfur complexes, showing the versatility of the electrode. DSSCs using these FGS electrodes had efficiencies (eta) equal to or higher than those using thermally decomposed chloroplatinic acid electrodes in each of the three major redox mediators: I (eta(FGS) = 6.8%, eta(Pt) = 6.8%), Co (4.5%, 4.4%), S (3.5%, 2.0%). Through an analysis of the thermolysis of the binder and composite material, we determined that the high surface area of an electrode, as determined by nitrogen adsorption, is consistent with but not sufficient for high performing electrodes. Two other important considerations are that (i) enough residue remains in the composite to maintain structural stability and prevent restacking of FGSs upon the introduction of the solvent, and (ii) this residue must not disperse in the electrolyte.
Li, X. L. ; Qi, W. ; Mei, D. H. ; Sushko, M. L. ; Aksay, I. ; Liu, J. Functionalized Graphene Sheets as Molecular Templates for Controlled Nucleation and Self-Assembly of Metal Oxide-Graphene Nanocomposites. Advanced Materials 2012, 24, 5136-5141.
Dabbs, D. M. ; Aksay, I. A. Multifunctional and Low-Density Inorganic Nanocomposites. JOM 2012, 64, 226-233.Abstract
We summarize our recent studies on the use of low-density nanoporous silica structures prepared through templating of a self-assembling disordered liquid-crystalline L (3) phase, as a matrix for use in numerous applications, including sensing, optical data storage, drug release, and structural. The silica matrix exhibits low density (0.5 g cm(-3) to 0.8 g cm(-3) for monoliths, 0.6 g cm(-3) to 0.99 g cm(-3) for fibers) coupled with high surface areas (up 1400 m(2) g(-1)) and void volumes (65% or higher). High-surface-area coatings are used to increase the sensitivity of mass-detecting quartz crystal microbalances to over 4000 times that of uncoated crystals. Monoliths, films, and fibers are produced using the templated silica gel. Once dried and converted to silica, the nanostructured material exhibits high fracture strength (up to 35 MPa in fibers) and Young's modulus (30 GPa to 40 GPa in fibers). These values are, respectively, two orders of magnitude and twice those of nanostructured silicas having comparable densities.
Ozbas, B. ; O'Neill, C. D. ; Register, R. A. ; Aksay, I. A. ; Prud'homme, R. K. ; Adamson, D. H. Multifunctional elastomer nanocomposites with functionalized graphene single sheets. Journal of Polymer Science Part B-Polymer Physics 2012, 50, 910-916.Abstract
We demonstrate the use of functionalized graphene sheets (FGSs) as multifunctional nanofillers to improve mechanical properties, lower gas permeability, and impart electrical conductivity for several distinct elastomers. FGS consists mainly of single sheets of crumbled graphene containing oxygen functional groups and is produced by the thermal exfoliation of oxidized graphite (GO). The present investigation includes composites of FGS and three elastomers: natural rubber (NR), styrenebutadiene rubber, and polydimethylsiloxane (PDMS). All of these elastomers show similar and significant improvements in mechanical properties with FGS, indicating that the mechanism of property improvement is inherent to the FGS and not simply a function of chemical crosslinking. The decrease in gas permeability is attributed to the high aspect ratio of the FGS sheets. This creates a tortuous path mechanism of gas diffusion; fitting the permeability data to the Nielsen model yields an aspect ratio of similar to 1000 for the FGS. Electrical conductivity is demonstrated at FGS loadings as low as 0.08% in PDMS and reaches 0.3 S/m at 4 wt % loading in NR. This combination of functionalities imparted by FGS is shown to result from its high aspect ratio and carbon-based structure. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. A. ; Chiang, K. S. ; Chen, C. - H. ; Prud'homme, R. K. Printed electronics, 2012.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an elec. conductive ink comprising functionalized graphene sheets and at least one binder. A method of prepg. printed electronic devices is further disclosed.
Ozbas, B. ; Toki, S. ; Hsiao, B. S. ; Chu, B. ; Register, R. A. ; Aksay, I. A. ; Prud'homme, R. K. ; Adamson, D. H. Strain-induced crystallization and mechanical properties of functionalized graphene sheet-filled natural rubber. Journal of Polymer Science Part B-Polymer Physics 2012, 50, 718-723.Abstract
The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain-induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain-induced crystallization of NR is compared by coupled tensile tests and X-ray diffraction experiments. Synchrotron X-ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS-filled NR samples compared with CB-filled NR, even at low loadings. Neat-NR exhibits strain-induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two-dimensional (2D) wide angle X-ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X-ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012