Publications

2016
Aksay, I. A. ; Alain-Rizzo, V. ; Bozym, D. J. ; Dabbs, D. M. ; Szamreta, N. ; Ustundag, C. B. Electrohydrodynamically Formed Structures of Cabonaceous Material, 2016.Abstract

The present invention relates generally to carbon structures and specifically to electrohydrodynamically formed structures of carbonaceous material.  Coatings, such as physically coherent films, coatings, membranes, or tapes made from high carbon content materials, such as graphene sheets, can be assembled using electrophoretic deposition, tape casting, spin casting, drop casting, or filtration.  Cast or filtered structures typically have to be at least 400 nm thick to provide continuity and mechanical stability.  Such structures contain flaws created by removing the liquid through drying or filtration.  In addition, such structures can have a reduced flexibility and compliance, which can result in an increase in susceptibility to damage during transfer and/or fitting to the item to be covered.  Similar to electrohydrodynamic deposition, electrophoretic deposition uses an applied electric field to attract particles or sheets to a surface having an overall charge opposite to the charge intrinsic to or induced on the particles or sheets, thereby coating the surface, as described in United States patent No. 2,894,888 to Shyne, et al., and United States patent No. 3,932,231 to Hara, et al., and many others.  However, in electrophoretic deposition the particles or sheets adhere at the point of initial contact to the substrate or previously deposited layers and remain fixed in position, which leaves defects or gaps between the particles or sheets comprising the layers that constitute the coating, membrane, or film.  A fully dense covering requires several layers, resulting in increased thickness of the coating, membrane, or film which limits its applications.

2015
Zhang, C. ; Dabbs, D. M. ; Liu, L. - M. ; Aksay, I. A. ; Car, R. ; Selloni, A. Combined Effects of Functional Groups, Lattice Defects, and Edges in the Infrared Spectra of Graphene Oxide. The Journal of Physical Chemistry C 2015, 119, 18167-18176.Abstract

Infrared spectroscopy in combination with density functional theory calculations has been widely used to characterize the structure of graphene oxide and its reduced forms. Yet, the synergistic effects of different functional groups, lattice defects, and edges on the vibrational spectra are not well understood. Here, we report first-principles calculations of the infrared spectra of graphene oxide performed on realistic, thermally equilibrated, structural models that incorporate lattice vacancies and edges along with various oxygen-containing functional groups. Models including adsorbed water are examined as well. Our results show that lattice vacancies lead to important blue and red shifts in the OH stretching and bending bands, respectively, whereas the presence of adsorbed water leaves these shifts largely unaffected. We also find unique infrared features for edge carboxyls resulting from interactions with both nearby functional groups and the graphene lattice. Comparison of the computed vibrational properties to our experiments clarifies the origin of several observed features and provides evidence that defects and edges are essential for characterizing and interpreting the infrared spectrum of graphene oxide.

Li, Y. ; Alain-Rizzo, V. ; Galmiche, L. ; Audebert, P. ; Miomandre, F. ; Louarn, G. ; Bozlar, M. ; Pope, M. A. ; Dabbs, D. M. ; Aksay, I. A. Functionalization of Graphene Oxide by Tetrazine Derivatives: A Versatile Approach toward Covalent Bridges between Graphene Sheets. Chemistry of Materials 2015, 27, 4298-4310.Abstract

We have covalently grafted tetrazine derivatives to graphene oxide through nucleophilic substitution. Since the tetrazine unit is electroactive and nitrogen-rich, with a reduction potential sensitive to the type of substituent and degree of substitution, we used electrochemistry and X-ray photoelectron spectroscopy to demonstrate clear evidence for grafting through covalent bonding. Chemical modification was supported by Fourier transform infrared spectroscopy and thermal analysis. Tetrazines grafted onto graphene oxide displayed different mass losses compared to unmodified graphene and were more stable than the molecular precursors. Finally, a bridging tetrazine derivative was grafted between sheets of graphene oxide to demonstrate that the separation distance between sheets can be maintained while designing new graphene-based materials, including chemically bound, redox structures.

2014
Pope, M. A. ; Alain-Rizzo, V. ; Lettow, J. S. ; Aksay, I. A. ; Dabbs, D. M. Batteries incorporating graphene membranes for extending the cycle-life of lithium-ion batteries. 62/012090, 2014.
2012
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. J. Am. Chem. Soc. 2012, 134, 19011-19016.
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.

Tessonnier, J. P. ; Haas, F. M. ; Dabbs, D. M. ; Dryer, F. L. ; Yetter, R. A. ; Barteau, M. A. Polyoxometalate Clusters Supported on Functionalized Graphene as Nanohybrids for the Catalytic Combustion of Liquid Fuels. MRS Symp. Proc., 2012, 1451, 137-143.
2011
Korkut, S. ; Roy-Mayhew, J. D. ; Dabbs, D. M. ; Milius, D. L. ; Aksay, I. A. High Surface Area Tapes Produced with Functionalized Graphene. ACS Nano 2011, 5 5214-5222.Abstract

We describe a scalable method for producing continuous graphene networks by tape casting surfactant-stabilized aqueous suspensions of functionalized graphene sheets. Similar to all other highly connected graphene-containing networks, the degree of overlap between the sheets controls the tapes' electrical and mechanical properties. However, unlike other graphene-containing networks, the specific surface area of the cast tapes remains high (>400 m(2).g(-1)). Exhibiting apparent densities between 0.15 and 0.51 g.cm(-3), with electrical conductivities up to 24 kS.m(-1) and tensile strengths over 10 MPa, these tapes exhibit the best combination of properties with respect to density heretofore observed for carbon-based papers, membranes, or films.

2009
Sabourin, J. L. ; Dabbs, D. M. ; Yetter, R. A. ; Dryer, F. L. ; Aksay, I. A. Functionalized Graphene Sheet Colloids for Enhanced Fuel/Propellant Combustion. ACS Nano 2009, 3 3945-3954.Abstract

We have compared the combustion of the monopropellant nitromethane with that of nitromethane containing colloidal particles of functionalized graphene sheets or metal hydroxides. The linear steady-state burning rates of the monopropellant and colloidal suspensions were determined at room temperature, under a range of pressures (3.35-14.4 MPa) using argon as a pressurizing fluid. The ignition temperatures were lowered and burning rates increased for the colloidal suspensions compared to those of the liquid monopropellant alone, with the graphene sheet suspension having significantly greater burning rates (i.e., greater than 175%). The relative change in burning rate from neat nitromethane increased with increasing concentrations of fuel additives and decreased with increasing pressure until at high pressures no enhancement was found.

2008
Sai, H. ; Dabbs, D. M. ; Aksay, I. A. Mechanical properties of L3-templated nanostructured silica. ACS Polymer Preprints 2008, 49, 546-547.
2007
Adamson, D. H. ; Dabbs, D. M. ; Pacheco, C. R. ; Giotto, M. V. ; Morse, D. E. ; Aksay, I. A. Non-peptide polymeric silicatein alpha mimic for neutral pH catalysis in the formation of silica. Macromolecules 2007, 40, 5710-5717.Abstract

We have synthesized a catalytically active polymer inspired by the naturally occurring protein silicatein alpha and have shown it to catalyze the formation of silica from tetraethoxysilane under near-neutral pH and ambient temperatures. We based the composition of the polymer on the functionalities found in silicatein alpha, specifically those essential components of the catalytically active site for the hydrolysis of silicon alkoxides. Our bioinspired polymer is a block copolymer of poly(2-vinylpyridine-b-1,2-butadiene), functionalized by the addition of hydroxyl groups via hydroboration chemistry. The catalytic action of our polymer on tetraethoxysilane at neutral pH and ambient temperature conditions has been confirmed using a modified molybdic acid assay method, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The structure of the resulting gel is investigated by scanning electron microscopy and solid-state nuclear magnetic resonance. The microscopic features of the material formed resemble that of gels formed by the acid-catalyzed hydrolysis of tetraethoxysilane.

2006
Malik, A. S. ; Dabbs, D. M. ; Katz, H. E. ; Aksay, I. A. Silica monoliths templated on L3 liquid crystal. Langmuir 2006, 22, 325-331.Abstract

Dimensionally stable, optically clear, highly porous (similar to 65% of the apparent volume), and high surface area (up to 1400 m(2)/g) silica monoliths were fabricated as thick disks (0.5 cm) by templating the isotropic liquid crystalline L-3 phase with silica through the hydrolysis and condensation of a silicon alkoxide and then removing the organic constituents by supercritical ethanol extraction. The L3 liquid crystal is a stable phase formed by the cosurfactants cetylpyridinium chloride monohydrate and hexanol in HCl(aq) solvent. Extracted 0.5 cm thick disks exhibited a low ratio of scattered to transmitted visible light (1.5 x 10(-6) at 22 from the surface normal). The degree of silica condensation in the monoliths was high, as determined by Si-29 NMR measurements of Q(3) and Q(4) peak intensities (0.53 and 0.47, respectively). As a result, the extracted and dried monoliths were mechanically robust and did not fracture when infiltrated by organic solvents. Photoactive liquid monomers were infiltrated into extracted silica monoliths and polymerized in situ, demonstrating the possible application of templated silica to optical storage technology.

Dabbs, D. M. ; Mulders, N. ; Aksay, I. A. Solvothermal removal of the organic template from L3 ("sponge") templated silica monoliths. Journal of Nanoparticle Research 2006, 8 603-614.Abstract

We compare the methods of continuous solvent (Soxhlet) and supercritical solvent extractions for the removal of the organic template from nanostructured silica monoliths. Our monoliths are formed by templating the L-3 liquid crystal phase of cetylpyridinium chloride in aqueous solutions with tetramethoxy silane. The monoliths that result from both Soxhlet and supercritical extraction methods are mechanically robust, optically clear, and free of cracks. The Soxhlet method compares favorably with supercritical solvent extraction in that equivalent L-3-templated silica can be synthesized without the use of specialized reactor hardware or higher temperatures and high pressures, while avoiding noxious byproducts. The comparative effectiveness of various solvents in the Soxhlet process is related to the Hildebrand solubility parameter, determined by the effective surface area of the extracted silica.

Bhansali, S. H. ; Malik, A. S. ; Jarvis, J. M. ; Akartuna, I. ; Dabbs, D. M. ; Carbeck, J. D. ; Aksay, I. A. The stability of L3 sponge phase in acidic solutions. Langmuir 2006, 22, 4060-4064.Abstract

In the synthesis of the disordered lyotropic liquid crystalline L-3 sponge phase prepared with the cosurfactants cetylpyridinium chloride and hexanol, aqueous NaCl solution is used as the solvent. When this sponge phase is used as the template for L3 silica-phase processing, we replace NaCl with HCl to facilitate the acid catalysis of tetramethoxysilane in forming a templated silica gel, assuming that changing the solvent from NaCl(aq) to HCl(aq) of equivalent ionic strength does not affect the stability range of the L3 phase. In this work, we confirm that changing the pH of the solvent from neutral to acidic (with HQ has negligible effect on the L3 phase region. Equivalent ionic strength is provided by either NaCl(aq) or HCl(aq) solvent; therefore, a similar phase behavior is observed regardless of which aqueous solvent is used.

2005
Dabbs, D. M. ; Ramachandran, U. ; Lu, S. ; Liu, J. ; Wang, L. Q. ; Aksay, I. A. Inhibition of aluminum oxyhydroxide precipitation with citric acid. Langmuir 2005, 21, 11690-11695.Abstract

Citric acid has been shown to act as an agent for increasing the solubility of aluminum oxyhydroxides in aqueous solutions of high (>2.47 mol/mol) hydroxide-to-aluminum ratios. Conversely, citric acid also colloidally stabilizes particles in aqueous suspensions of aluminum-containing particles. Solutions of aluminum chloride, with and without citric acid added, were titrated with NaOH(aq), The presence and size of particles were determined using quasi-elastic light scattering. In solutions that contained no citric acid, particles formed instantaneously when NaOH(aq) was added but these were observed to rapidly diminish in size, disappearing at OH/Al ratios below 2.5 mol/mol. When the OH/Al ratio was raised beyond 2.5 by adding more NaOH(aq), suspensions of colloidally stable particles formed. Large polycations containing 13 aluminum atoms were detected by Al-27 solution NMR in citric-acid-free solutions with OH/Al ratios slightly lower than 2.5. In comparison, adding citric acid to solutions of aluminum chloride inhibited the formation of large aluminum-containing polycations. The absence of the polycations prevents or retards the subsequent formation of particles, indicating that the polycations, when present, act as seeds to the formation of new particles. Particles did not form in solutions with a citric acid/aluminum ratio of 0.8 until sufficient NaOH(aq) was added to raise the OH/Al ratio to 3.29. By comparison, lower amounts of citric acid did not prevent particles from forming but did retard the rate of growth.

2004
Adamson, D. H. ; Dabbs, D. M. ; Morse, D. E. ; Aksay, I. A. Non-peptide, Silicatein-α inspired silica condensation catalyst. ACS Abstracts 2004, 227, 145.
2003
McGrath, K. M. ; Dabbs, D. M. ; Aksay, I. A. ; Gruner, S. M. Lyotropic Liquid Crystalline L3 Phase Silicated Nanoporous Monolithic Composites and Their Production, 2003.
Cates, G. D. ; Aksay, I. A. ; Happer, W. ; Hsu, M. F. ; Dabbs, D. M. Sol-Gel Coated Polarization Vessels, 2003.
2001
Malik, A. - S. ; Dabbs, D. M. ; Aksay, I. A. ; Katz, H. E. Disordered mesoporous silicates formed by templation of a liquid crystal (L3). Solid-State Chemistry of Inorganic Materials III, 2001.
2000
Dabbs, D. M. ; Aksay, I. A. Self-assembled ceramics produced by complex-fluid templation. Annual Review of Physical Chemistry 2000, 51, 601-622.Abstract

This review examines the use of self-assembly in the fabrication of ceramic mesostructures, emphasizing the use of amphiphilic surfactants and block copolymers. The association between this area of research and biomimetics is discussed, linking developments in synthetic self-assembly with biomineralization. The fabrication of hierarchical structures through the use of simultaneous processing is shown to be a necessary condition for applications of this new technology.

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