The reinforcing component of these articles includes a compn. made from at least one polymer and graphene sheets. [on SciFinder(R)]

A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from ∼300-2600 m2/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as detd. by x-ray diffraction. [on SciFinder(R)]

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 bionanocomposite film consisting of glucose oxidase/Pt/functional graphene sheets/chitosan (GOD/Pt/FGS/chitosan) for glucose sensing is described. With the electrocatalytic synergy of FGS and Pt nanoparticles to hydrogen peroxide, a sensitive biosensor with a detection limit of 0.6 mu M glucose was achieved. The biosensor also has good reproducibility, long-term stability and negligible interfering signals from ascorbic acid and uric acid comparing with the response to glucose. The large surface area and good electrical conductivity of graphene suggests that graphene is a potential candidate as a sensor material. The hybrid nanocomposite glucose sensor provides new opportunity for clinical diagnosis and point-of-care applications.

Direct electrochemistry of a glucose oxidase (GOD)-graphene-chitosan nanocomposite was studied. The immobilized enzyme retains its bioactivity, exhibits a surface confined, reversible two-proton and two-electron transfer reaction, and has good stability, activity and a fast heterogeneous electron transfer rate with the rate constant (k(s)) of 2.83 s(-1). A much higher enzyme loading (1.12 x 10(-9) mol/cm(2)) is obtained as compared to the bare glass carbon surface. This GOD-graphene-chitosan nanocomposite film can be used for sensitive detection of glucose. The biosensor exhibits a wider linearity range from 0.08 mM to 12 mM glucose with a detection limit of 0.02 mM and much higher sensitivity (37.93 mu A mM(-1) cm(-2)) as compared with other nanostructured supports. The excellent performance of the biosensor is attributed to large surface-to-volume ratio and high conductivity of graphene, and good biocompatibility of chitosan, which enhances the enzyme absorption and promotes direct electron transfer between redox enzymes and the surface of electrodes.

We used anionic sulfate surfactants to assist the stabilization of graphene in aqueous solutions and facilitate the self-assembly of in situ grown nanocrystalline TiO2, rutile and anatase, with graphene. These nanostructured TiO2-graphene hybrid materials were used for investigation of Li-ion insertion properties. The hybrid materials showed significantly enhanced Li-ion insertion/extraction in TiO2. The specific capacity was more than doubled at high charge rates, as compared with the pure TiO2 phase. The improved capacity at high charge-discharge rate may be attributed to increased electrode conductivity in the presence of a percolated graphene network embedded into the metal oxide electrodes.

This paper established a necessary condition for the sintering of powder compacts by examining the total free energy balance in terms of the particle size, neck size and contact number. The thermodynamic analysis of the proposed model clarifies the relation of shrinkage (q) of powder compact-contact angle (phi)-relative density at a given dihedral angle (phi(e)) of a grain boundary. Faster densification proceeds in the region with a larger coordination number (n) of particles at a small q value. A large shrinkage is needed to eliminate the large pores formed in the structure of small n value. Full density can be achieved in the range of 117 degrees

The present invention is a bridged graphite oxide material, comprising at least two graphite oxide sheets in which a plurality of graphite oxide sheets are bridged to at least one other graphite oxide sheet by at least one diamine bridging group. The bridged graphite oxide is formed by the covalent reaction of one amino group of a diamine with a reactive group on the surface or edge of one graphite oxide sheet and the covalent reaction of another amino group of the same diamine with a reactive group on the surface or edge of another graphite oxide sheet. The bridged graphite oxide material may be incorporated in polymer composites or used in hydrogen adsorption media. [on SciFinder(R)]

Functionalized graphene sheets having a carbon to oxygen molar ratio of at least about 23:1. A polymer composite comprises the functionalized graphene sheet and ≥1 polymer. [on SciFinder(R)]

Measuring the dissolution dynamics of thin films in situ both with spatial and temporal resolution can be a challenging task. Available methods such as scanning electrochemical microscopy rely on scanning the specimen and are intrinsically slow. We developed a characterization technique employing only an optical microscope, a digital charge coupled device camera, and a computer for image processing. It is capable of detecting dissolution rates of the order of nm/min and has a spatial and temporal resolution which is limited by the imaging and recording setup. We demonstrate the capabilities of our method by analyzing the electrochemical dissolution of copper thin films on gold substrates in a mild hydrochloric acid solution. Due to its simplicity, our technique can be implemented in any laboratory and can be applied to a variety of systems such as thin film sensors or passive coatings.

We present a molecular dynamics simulation study of the structure and dynamics of water confined between silica surfaces using beta-cristobalite as a model template. We scale the surface Coulombic charges by means of a dimensionless number, k, ranging from 0 to 1, and thereby we can model systems ranging frorn hydrophobic apolar to hydrophilic, respectively. Both rotational and translational dynamics exhibit a nonmonotonic dependence on k characterized by a maximum in the in-plane diffusion coefficient, D-parallel to, at values between 0.6 and 0.8, and a minimum in the rotational relaxation time, tau(R), at k = 0.6. The slow dynamics observed in the proximity of the hydrophobic apolar surface are a consequence of beta-cristobalite templating an ice-like water layer. The fully hydrophilic surfaces (k = 1.0), on the other hand, result in slow interfacial dynamics due to the presence of dense but disordered water that forms strong hydrogen bonds with surface silanol groups. Confinement also induces decoupling between translational and rotational dynamics, as evidenced by the fact that TR attains values similar to that of the bulk, while D-parallel to is always lower than in the bulk. The decoupling is characterized by a more drastic reduction in the translational dynamics of water compared to rotational relaxation.

Electrocatalysis of oxygen reduction using Pt nanoparticles supported on functionalized graphene sheets (FGSs) was studied. FGSs were prepared by thermal expansion of graphite oxide. Pt nanoparticles with average diameter of 2 nm were uniformly loaded on FGSs by impregnation methods. Pt-FGS showed a higher electrochemical surface area and oxygen reduction activity with improved stability as compared with the commercial catalyst. Transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization suggest that the improved performance of Pt-FGS can be attributed to smaller particle size and less aggregation of Pt nanoparticles on the functionalized graphene sheets.

We use molecular dynamics simulations to study the influence of confinement on the dynamics of a nanoscopic water film at T = 300 K and rho = 1.0 g cm(-3). We consider two infinite hydrophilic (beta-cristobalite) silica surfaces separated by distances between 0.6 and 5.0 nm. The width of the region characterized by surface-dominated slowing down of water rotational dynamics is similar to 0.5 nm, while the corresponding width for translational dynamics is similar to 1.0 nm. The different extent of perturbation undergone by the in-plane dynamic properties is evidence of rotational-translational decoupling. The local in-plane rotational relaxation time and translational diffusion coefficient collapse onto confinement-independent "master" profiles as long as the separation d >= 1.0 nm. Long-tithe tails in the perpendicular component of the dipole moment autocorrelation function are indicative of anisotropic behavior in the rotational relaxation.

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 sp(2) 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 sp(3) carbons on the edges of a zigzag carbon ribbon.

Using liquid-cell atomic force microscopy, we investigate aqueous solutions of alkyltrimethylammonium halide surfactants at the Au(III) 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.

A polymer compn. comprises a polymer matrix comprising an elastomer, and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by X-ray diffraction. The functional graphene-contg. polymer compns. have excellent strength, toughness, thermal stability, elec. cond., and can be used for prodn. of gas-barrier materials. Thus, films (200-400 μm) made of a silicone rubber RTV 615 compn. contg. 5% of functional graphene nanoparticles had a Young's modulus 12.18 and a tensile strength 6.52 times higher than the resp. values for neat rubber. Similar films made of a silicone rubber RTV 615 compn. contg. 5% of clay nanoparticles had a Young's modulus 1.28 and a tensile strength 2.38 times higher than the resp. values for neat rubber. [on SciFinder(R)]

A gas diffusion barrier contains a polymer (e.g., natural rubber) matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by X-ray diffraction. [on SciFinder(R)]

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.

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.

A Reply to the Comment by Manuel Gamero-Castano.

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.

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.

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(1). 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(2-11). 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 polyacrylonitrile) 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.

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 similar to 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.

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. (C) 2008 American Institute of Physics.

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.

A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from ∼300 m2/g to 2600 m2/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as detd. by x-ray diffraction. The modified graphite oxide is useful in nanocomposites with, e.g., PMMA. [on SciFinder(R)]

To elucidate the nature of processes involved in electrically driven particle aggregation in steady fields, flows near a charged spherical colloidal particle next to an electrode were studied. Electrical body forces in diffuse layers near the electrode and the particle surface drive an axisymmetric flow with two components. One is electroosmotic flow (EOF) driven by the action of the applied field on the equilibrium diffuse charge layer near the particle. The other is electrohydrodynamic (EHD) flow arising from the action of the applied field on charge induced in the electrode polarization layer. The EOF component is proportional to the current density and the particle surface (zeta) potential, whereas our scaling analysis shows that the EHD component scales as the product of the current density and applied potential. Under certain conditions, both flows are directed toward the particle, and a superposition of flows from two nearby particles provides a mechanism for aggregation. Analytical calculations of the two flow fields in the limits of infinitesimal double layers and slowly varying current indicate that the EOF and EHD flow are of comparable magnitude near the particle whereas in the far field the EHD flow along the electrode is predominant. Moreover, the dependence of EHD flow on the applied potential provides a possible explanation for the increased variability in aggregation velocities observed at higher field strengths.

While exhibiting a well-defined nanometer-level structure, surfactant-templated nanoscopic silicas produced via self-assembly do not always possess long-range order. We demonstrate that long-range order can be controlled by guiding the self-assembly of nanostructured silica-surfactant hybrids with low-strength electric fields (E similar to 200 V/m) to produce nanoscopic silica with both the micrometer- and nanometer-level structures oriented parallel to the applied field. Under the influence of the electric field, nanoscopic silica particles migrate, elongate, and merge into fibers with a rate of migration proportional to the applied field strength. The linear dependence with the field strength indicates that the process is governed by electroosmotic flow but not by polarization effects. Realignment of the short-range ordered surfactant nanochannels along the fiber axis accompanies the migration.

Electrohydrodynamic (EHD) flow around a charged spherical colloid near an electrode was studied theoretically and experimentally to understand the nature of long-range particle-particle attraction near electrodes. Numerical computations for finite double-layer thicknesses confirmed the validity of an asymptotic methodology for thin layers. Then the electric potential around the particle was computed analytically in the limit of zero Peclet number and thin double layers for oscillatory electric fields at frequencies where Faradaic reactions are negligible. Streamfunctions for the steady component of the EHD flow were determined with an electro-osmotic slip boundary condition on the electrode surface. Accordingly, it was established how the axisymmetric flow along the electrode is related to the dipole coefficient of the colloidal particle. Under certain conditions, the flow is directed toward the particle and decays as r(-4), in accord with observations of long-range particle aggregation. To test the theory, particle-tracking experiments were performed with fluorescent 300 nm particles around 50 mu m particles over a wide range of electric field strengths and frequencies. Treating the particle surface conductivity as a fitting parameter yields velocities in excellent agreement with the theoretical predictions. The observed frequency dependence, however, differs from the model predictions, suggesting that the effect of convection on the charge distribution is not negligible as assumed in the zero Peclet number limit.

The intercalation reaction of graphite oxide with diaminoalkanes, with the general formula H2N(CH2)(n)NH2 (n = 4-10), was studied as a method for synthesizing pillared graphite with tailored interlayer spacing. Interlayer spacings from 0.8 to 1.0 nm were tailored by varying the size of the intercalant from (CH2)(4) to (CH2)(10). X-ray diffraction and infrared spectroscopy were used to confirm intercalation, and the frequency of the CH2 stretch confirmed that the intercalants are in a disordered state, with an important contribution from the gauche conformer. Sequential intercalation of diaminoalkanes followed by dodecylamine demonstrated the inability of these "stitched" systems to undergo expansion along the c-direction, indicative of cross-linking. Finally, the reaction of graphite oxide with diaminoalkanes under reflux and for extended periods (> 72 h) resulted in the chemical reduction of the graphite oxide to a disordered graphitic structure.

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.

A detailed analysis of the thermal expansion mechanism of graphite oxide to produce functionalized graphene sheets is provided. Exfoliation takes place when the decomposition rate of the epoxy and hydroxyl sites of graphite oxide exceeds the diffusion rate of the evolved gases, thus yielding pressures that exceed the van der Waals forces holding the graphene sheets together. A comparison of the Arrhenius dependence of the reaction rate against the calculated diffusion coefficient based on Knudsen diffusion suggests a critical temperature of 550 degrees C which must be exceeded for exfoliation to occur. As a result of their wrinkled nature, the functionalized and defective graphene sheets do not collapse back to graphite oxide but are highly agglomerated. After dispersion by ultrasonication in appropriate solvents, statistical analysis by atomic force microscopy shows that 80% of the observed flakes are single sheets.

We demonstrate improved atomic force microscopic imaging of surfactant surface aggregates, featuring an increase in the topography contrast by several hundred percent with respect to all previous studies. Surfactant aggregates on rough gold surfaces, which could not be imaged previously because of low resolution, display substantially different morphologies when compared with atomically smooth materials.

A pulsed electrohydrodynamic jet can produce on-demand drops much smaller than the delivery nozzle. This letter describes an experimentally validated model for electrically pulsed jets. Viscous drag in a thin nozzle limits the flow rate and leads to intrinsic pulsations of the cone jet. A scale analysis for intrinsic cone-jet pulsations is derived to establish the operating regime for drop deployment. The scaling laws are applicable to similar electrohydrodynamic processes in miniaturized electrospraying systems. (c) 2006 American Institute of Physics.

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.

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.

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.

Orientational order of surfactant micelles and proteins on crystalline templates has been observed but, given that the template unit cell is significantly smaller than the characteristic size of the adsorbate, this order cannot be attributed to lattice epitaxy. We interpret the template-directed orientation of rodlike molecular assemblies as arising from anisotropic van der Waals interactions between the assembly and crystalline surfaces where the anisotropic van der Waals interaction is calculated using the Lifshitz methodology. Provided the assembly is sufficiently large, substrate anisotropy provides a torque that overcomes rotational Brownian motion near the surface. The probability of a particular orientation is computed by solving a Smoluchowski equation that describes the balance between van der Waals and Brownian torques. Torque aligns both micelles and protein fibrils; the interaction energy is minimized when the assembly lies perpendicular to a symmetry axis of a crystalline substrate. Theoretical predictions agree with experiments for both hemi-cylindrical micelles and protein fibrils adsorbed on graphite.

The "drop-and-place" paradigm aims at delivering and positioning liquid drops using a pulsed electrohydrodynamic jet. On-demand drops much smaller than the diameter of the delivery nozzle may also contain particles. We report proof-of-concept experiments on the delivery of single 2 mu m diameter particles using a 50 mu m nozzle and identify the control parameters for dosing and positioning accuracies. A positioning accuracy at the micrometer level is achieved by eliminating contact line pinning on a hydrophobic surface and minimizing impingement-induced motion. The dosing statistics follow the random Poisson distribution, indicating that single-particle accuracy can be achieved using a gating mechanism. (c) 2006 American Institute of Physics.

We present a strategy to increase the sensitivity of resonators to the presence of specific molecules in the gas phase, measured by the change in resonant frequency as the partial pressure of the molecule changes. We used quartz crystals as the resonators and coated them with three different thin films (< 1 mu m thick) of porous silica: silica xerogel, silica templated by an ordered hexagonal phase of surfactant micelles, and silica templated by an isotropic L-3 phase surfactant micellar system. We compared the sensitivity of coated resonators to the presence of water vapor. The crystals coated with hexagonal phase-templated silica displayed a sensitivity enhancement up to 100-fold compared to an uncoated quartz crystal in the low-pressure regime where adsorption played a dominant role. L-3 phase-templated silica displayed the highest sensitivity (up to a 4000-fold increase) in the high partial pressure regimes where capillary condensation was the main accumulation mechanism. Three parameters differentiate the contributions of these coatings to the sensitivity of the underlying resonator: (i) specific surface area per unit mass of the coating, (ii) accessibility of the surfaces to a target molecule, and (iii) distribution in the characteristic radii of curvature of internal surfaces, as measured by capillary condensation.

A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting.

Surfactant micelles form oriented arrays on crystalline substrates although registration is unexpected since the template unit cell is small compared to the size of a rodlike micelle. Interaction energy calculations based on molecular simulations reveal that orientational energy differences on a molecular scale are too small to explain matters. With atomic force microscopy, we show that orientational ordering is a dynamic, multimolecule process. Treating the cooperative processes as a balance between van der Waals torque on a large, rodlike micellar assembly and Brownian motion shows that orientation is favored.

Optical microscope images of graphite oxide (GO) reveal the occurrence of fault lines resulting from the oxidative processes. The fault lines and cracks of GO are also responsible for their much smaller size compared with the starting graphite materials. We propose an unzipping mechanism to explain the formation of cracks on GO and cutting of carbon nanotubes in an oxidizing acid. GO unzipping is initiated by the strain generated by the cooperative alignment of epoxy groups on a carbon lattice. We employ two small GO platelets to show that through the binding of a new epoxy group or the hopping of a nearby existing epoxy group, the unzipping process can be continued during the oxidative process of graphite. The same epoxy group binding pattern is also likely to be present in an oxidized carbon nanotube and cause its breakup.

The present invention provides thermal insulator composites based upon nanostructured L3-silica microparticles and polyurethane foam chem. that are both easy to process and have superior insulating properties for use in household and com. refrigeration, construction, and shipping applications. The composite material retains many of the attractive processing characteristics of polyurethane foams such as vol. expansion and shape-filling during polymn. and demonstrates a total thermal cond. between 32% and 44% that of com. available polyurethane foams. [on SciFinder(R)]

The patterning of ceramic thin films is of great interest for use in MEMS and other applications as discussed in the chapters by Maeda et al. and by Muralt and Baborowski. However, the complex chemistries of certain materials make the use of traditional photolithography techniques prohibitive. In this chapter, a number of low-cost, high throughput techniques for the patterrning of ceramic thin films derived from chemical solution precursors, such as sol-gels and ceramic slurries, are presented. Most of these methods are derived from soft lithographic methods using elastomer molds, a method that is categorized as the next generation lithography in the chapter by Alexe et al. Two categories of techniques are discussed: first, the focus is on methods that rely on the principles of confinement within the physical features of the mold to define the pattern on the substracte surface. Then, subtractive patterning techniques that rely on transferring a pattern to a spin-cast large-area continuous thin film are described. Most techniques have been demonstrated with fidelities on the order of 100 nm; however, their inability to precisely register and align the patterns as part of a hierarchical fabrication scheme has hindered their commercial implementation thus far. This chaper has been updated from the original manuscript to reflect the most recent available literature and complements the chapter by Baborowshi on pattern formation by micromachining techniques.

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.

A new patterning technique for the deposition of sol-gels and chemical solution precursors was developed to address some of the limitations of soft lithography approaches. When using micromolding in capillaries to pattern precursors that exhibit large amounts of shrinkage during drying, topographical distortions develop. In place of patterning the elastomeric mold, the network of capillary channels was patterned directly into the substrate surface and an elastomer membrane is used to complete the channels. When the wetting properties of the substrate surfaces were carefully controlled using self-assembled monolayers (SAMs), lead zirconate titanate thin films with nearly rectangular cross-sections were successfully patterned. This technique, called microchannel molding (mu CM), also provided a method for aligning multiple layers such as bottom electrodes for device fabrication.

The modern theory of dispersion forces uses macroscopic dielectric functions epsilon(omega) as a central ingredient. We reexamined the formalism and found that at separation distance < 2 nm the full dielectric function epsilon(omega,k) is needed. The use of epsilon(omega,k) results in as much as 30% reduction of the calculated Hamaker constants reported in the current literature. At larger distances, the theory reduces to the traditional method, which uses dielectric functions in the long-wavelength limit. We illustrate the formalism using the example of interaction between two graphite slabs. This example is of importance for intercalation and exfoliation of graphite and for the use of exfoliated graphite in composite materials. The formalism can also be extended to study anisotropic van der Waals interactions.