Publications by Year: 2014

2014
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. A. ; Chiang, K. S. ; Chen, C. - H. ; Prud'homme, R. K. Printed electronics, 2014.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Prud'homme, R. K. ; Aksay, I. A. Conductive circuit containing a polymer composition containing thermally exfoliated graphite oxide and method of making the same, 2014.Abstract
A conductive circuit containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, I. A. ; Saville, D. A. ; Poon, H. F. ; Korkut, S. ; Chen, C. - H. Electrohydrodynamic printing and manufacturing, 2014.Abstract
An stable electrohydrodynamic filament is obtained by causing a straight electrohydrodynamic filament formed from a liquid to emerge from a Taylor cone, the filament having a diameter of from 10 nm to 100 µm. Such filaments are useful in electrohydrodynamic printing and manufacturing techniques and their application in liquid drop/particle and fiber production, colloidal deployment and assembly, and composite materials processing.
Tavakol, B. ; Bozlar, M. ; Punckt, C. ; Froehlicher, G. ; Stone, H. A. ; Aksay, I. A. ; Holmes, D. P. Buckling of dielectric elastomeric plates for soft, electrically active microfluidic pumps. Soft Matter 2014, 10, 4789-4794.Abstract
Elastic instabilities, when properly implemented within soft, mechanical structures, can generate advanced functionality. In this work, we use the voltage-induced buckling of thin, flexible plates to pump fluids within a microfluidic channel. The soft electrodes that enable electrical actuation are compatible with fluids, and undergo large, reversible deformations. We quantified the onset of voltage-induced buckling, and measured the flow rate within the microchannel. This embeddable, flexible microfluidic pump will aid in the generation of new stand-alone microfluidic devices that require a tunable flow rate.
Vijayakumar, M. ; Schwenzer, B. ; Shutthanandan, V. ; Hu, J. Z. ; Liu, J. ; Aksay, I. A. Elucidating graphene-ionic liquid interfacial region: A combined experimental and computational study. Nano Energy 2014, 3 152-158.Abstract
Graphene and ionic liquids are promising candidates for electrode materials and electrolytes, respectively, for modern energy storage devices such as supercapacitors. Understanding the interactions at the interfacial region between these materials is crucial for optimizing the overall performance and efficiency of supercapacitors. The interfacial region between graphene and an imidazolium-based ionic liquid is analyzed in a combined experimental and computational study. This dual approach reveals that the imidazolium-based cations mostly orient themselves parallel to the graphene surface due to pi-pi stacking interaction and form a primary interfacial layer, which is subsequently capped by a layer of anions from the ionic liquid. However, it also becomes apparent that the molecular interplay at the interfacial region is highly influenced by functional group defects on the graphene surface, in particular by hydroxyl groups. (C) 2012 Elsevier Ltd. All rights reserved.
Xiao, J. ; Meduri, P. ; Chen, H. H. ; Wang, Z. G. ; Gao, F. ; Hu, J. Z. ; Feng, J. ; Hu, M. ; Dai, S. ; Brown, S. ; et al. Energetics of Defects on Graphene through Fluorination. ChemSusChem 2014, 7 1295-1300.Abstract

Functionalized graphene sheets (FGSs) comprise a unique member of the carbon family, demonstrating excellent electrical conductivity and mechanical strength. However, the detailed chemical composition of this material is still unclear. Herein, we take advantage of the fluorination process to semiquantitatively probe the defects and functional groups on graphene surface. Functionalized graphene sheets are used as substrate for low-temperature (<150 °C) direct fluorination. The fluorine content has been modified to investigate the formation mechanism of different functional groups such as CF, CF2, OCF2 and (C=O)F during fluorination. The detailed structure and chemical bonds are simulated by density functional theory (DFT) and quantified experimentally by nuclear magnetic resonance (NMR). The electrochemical properties of fluorinated graphene are also discussed extending the use of graphene from fundamental research to practical applications.

Roy-Mayhew, J. D. ; Aksay, I. A. Graphene Materials and Their Use in Dye-Sensitized Solar Cells. Chemical Reviews 2014, 114, 6323-6348.
Punckt, C. ; Pope, M. A. ; Aksay, I. A. High Selectivity of Porous Graphene Electrodes Solely Due to Transport and Pore Depletion Effects. Journal of Physical Chemistry C 2014, 118, 22635-22642.Abstract
We contrast the performance of monolayer electrodes and thin porous film electrodes of highly reduced functionalized graphene to demonstrate that the introduction of electrode porosity gives rise to strong apparent electrocatalytic effects resulting in vastly improved electrode selectivity. This is despite graphene showing no intrinsic advantage over glassy carbon electrodes when used as a monolayer. The simultaneous electrooxidation of ascorbic acid, dopamine and uric acid is used as an experimental model electrolyte system. Our results suggest that a large number of reports claiming the superior surface chemistry of carbon nanomaterials as the reason for outstanding electrochemical characteristics should be revisited considering electrode morphology as a significant contributor to the observed behavior. Our experimental results are supported by numerical simulations explaining the porosity-induced electrode selectivity by the dominance of pore depletion over diffusion-limited currents.