Enhanced thermal decomposition of nitromethane on functionalized graphene sheets: ab initio molecular dynamics simulations.

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, functionalized 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 H(2)O, CO(2), 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.

High surface area tapes produced with functionalized graphene.

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.

Functionalized graphene sheet colloids for enhanced fuel/propellant combustion.

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.

The stability of L3 sponge phase in acidic solutions.

In the synthesis of the disordered lyotropic liquid crystalline L3 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 HCl) 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.

Silica monoliths templated on L3 liquid crystal.

Dimensionally stable, optically clear, highly porous (approximately 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 L(3) 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 degrees from the surface normal). The degree of silica condensation in the monoliths was high, as determined by (29)Si 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.

Inhibition of aluminum oxyhydroxide precipitation with citric acid.

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 (27)Al 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.