Sublimation and Diffusion Kinetics of 2,4,6-Trinitrotoluene (TNT) Single Crystals by Atomic Force Microscopy (AFM).

In this article, we report the in-situ nanoscale experimental measurement of sublimation rates, activation energy of sublimation, and diffusion coefficients of 2,4,6-trinitrotoluene (TNT) single crystals in air using atomic force microscopy (AFM). The crystals were prepared by slow evaporation at 5 °C using acetone-dissolved TNT. The mass loss was calculated by monitoring the shrinkage of the surface area of layered islands formed on the surface of the TNT crystals due to sublimation upon isothermal heating at temperatures below the melting point.

Investigation of Size-Dependent Sublimation Kinetics of 2,4,6-Trinitrotoluene (TNT) Micro-Islands Using In Situ Atomic Force Microscopy.

Kinetic thermal analysis was conducted using in situ atomic force microscopy (AFM) at a temperature range of 15-25 °C to calculate the activation energy of the sublimation of 2,4,6-trinitrotoluene (TNT) islands. The decay of different diameter ranges (600-1600 nm) of TNT islands was imaged at various temperatures isothermally such that an activation energy could be obtained. The activation energy of the sublimation of TNT increases as the diameter of islands increases.

Non-Isothermal Sublimation Kinetics of 2,4,6-Trinitrotoluene (TNT) Nanofilms.

Non-isothermal sublimation kinetics of low-volatile materials is more favorable over isothermal data when time is a crucial factor to be considered, especially in the subject of detecting explosives. In this article, we report on the in-situ measurements of the sublimation activation energy for 2,4,6-trinitrotoluene (TNT) continuous nanofilms in air using rising-temperature UV-Vis absorbance spectroscopy at different heating rates. The TNT films were prepared by the spin coating deposition technique.

Large-area preparation of high-quality and uniform three-dimensional graphene networks through thermal degradation of graphene oxide-nitrocellulose composites.

We demonstrate a simple method to prepare high-quality and uniform three-dimensional (3D) graphene networks through thermal degradation of graphene oxide (GO)-nitrocellulose composites over a large area. The nitrocellulose simultaneously acts as a support and aids in the reduction of GO by exothermic decomposition. The graphene networks have tunable porous morphology where the pore size can be controlled by adjusting the concentration of GO in the composite.

Polyethylenimine facilitated ethyl cellulose for hexavalent chromium removal with a wide pH range.

Ethyl cellulose (EC) composites modified with 20.0 wt % polyethylenimine (PEI) (PEI/ECs) demonstrated effective hexavalent chromium, [Cr(VI)], removal from solutions with a wide pH range. For example, 4.

Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.

The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets.

Preparation of sub-micron nitrocellulose particles for improved combustion behavior.

A novel method to prepare sub-micron nitrocellulose particles with spherical shape is demonstrated. The morphology of the nitrocellulose can be controlled by the solvent and the growth temperature. Using dimethylformamide (DMF) at a growth temperature is 5°C, reproducibly yielded spherical nitrocellulose particles.

Tip induced crystallization lithography.

We demonstrate a new technique for efficiently fabricating large-area organic crystal arrays on substrates using tip induced crystallization lithography (TICL). This technique depends on coating an amorphous organic thin film on a substrate and then inducing crystallization of the thin film using an atomic force microscope tip. After the noncrystalline materials are removed from the substrate by heating or washing, the organic crystal arrays are stable on the substrate.

Aerobic Oxidation of 9H-Fluorenes to 9-Fluorenones using Mono-/Multilayer Graphene-Supported Alkaline Catalyst.

The synthesis of 9-fluorenone derivatives has been achieved in high yield and with high purity by aerobic oxidation of 9H-fluorenes at room temperature in the presence of a graphene-supported KOH composite that acts as a catalyst in N,N-dimethylformamide. The new protocol involves very simple work-up procedures, and the solvent and the catalyst can be recycled and reused. A scaled-up preparative study employing this method was also conducted and showed its advantages of being both cost-effective and environmentally friendly, and has potential for application in industrial processes.

Effect of humidity and hydrophobicity on the tribological properties of self-assembled monolayers.

The tribological properties of two distinctive alkanethiol SAMs, 16-mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT), on gold substrates in various humidity conditions were examined by lateral force microscopy (LFM). The results suggest that hydrophobic ODT SAM is insensitive to humidity. The difference of lateral force signal is within ±10% regardless of humidity.

In situ direct measurement of vapor pressures and thermodynamic parameters of volatile organic materials in the vapor phase: benzoic acid, ferrocene, and naphthalene.

We report the direct determination of vapor pressures and optical and thermodynamic parameters of powders of low-volatile materials in their vapor phase using a commercial UV/Vis spectrometer. This methodology is based on the linear proportionality between the density of the saturated gas of the material and the absorbance of the gas at different temperatures. The vapor pressure values determined for benzoic acid and ferrocene are in good agreement with those reported in the literature with ∼2-7 % uncertainty.

Metal-organic frameworks (MOFs) as safer, structurally reinforced energetics.

Second-generation cobalt and zinc coordination architectures were obtained through efforts to stabilize extremely sensitive and energetic transition-metal hydrazine perchlorate ionic polymers. Partial ligand substitution by the tridentate hydrazinecarboxylate anion afforded polymeric 2D-sheet structures never before observed for energetic materials. Carefully balanced reaction conditions allowed the retention of the noncoordinating perchlorate anion in the presence of a strongly chelating hydrazinecarboxylate ligand.

Embossing of organic thin films using a surfactant assisted lift-off technique.

A simple technique for patterning organic materials using a surfactant assisted lift-off method is proposed. Thin films of various organic materials are prepared, and areas in contact with a surfactant coated poly(dimethylsiloxane) (PDMS) stamp are selectively removed. The general applicability of this technique is shown for materials containing nitrate, amine, and carboxylic acid functional groups.

Rapid estimation of thermodynamic parameters and vapor pressures of volatile materials at nanoscale.

Non-isothermal measurements of thermodynamic parameters and vapor pressures of low-volatile materials are favored when time is a crucial factor to be considered, such as in the case of detection of hazardous materials. In this article, we demonstrate that optical absorbance spectroscopy can be used non-isothermally to estimate the thermodynamic properties and vapor pressures of volatile materials with good accuracy. This is the first method to determine such parameters in nanoscale in just minutes.

Ionic polymers as a new structural motif for high-energy-density materials.

Energetic materials have been used for nearly two centuries in military affairs and to cut labor costs and expedite laborious processes in mining, tunneling, construction, demolition, and agriculture, making a tremendous contribution to the world economy. Yet there has been little advancement in the development of altogether new energetic motifs despite long-standing research efforts to develop superior materials. We report the discovery of new energetic compounds of exceptionally high energy content and novel polymeric structure which avoid the use of lead and mercury salts common in conventional primary explosives.

Thermo-optical determination of vapor pressures of TNT and RDX nanofilms.

Accurate thermodynamic parameters of thin films of explosives are important for understanding their behavior in the nanometer scale as well as in standoff detection. Using UV-absorbance spectroscopy technique, accurate thermodynamic parameters such as activation energies of sublimation, sublimation rates, and vapor pressures of the explosives cyclotrimethylenetrinitramine (RDX) and 2,4,6-trinitrotoluene (TNT) were determined. The values of these parameters are in excellent agreement with those reported using traditional experiments based on gravimetry.

Measuring the activation energy of thiol desorption using lateral force microscopy.

Thermal stability of self-assembled monolayers (SAMs) is important for applications in various surface science applications. As a model material, 16-mercaptohexadecanoic acid (MHA) on template stripped gold surfaces was investigated to determine the effect of temperature on the change of lateral force signal using atomic force microscopy (AFM). Friction force signals were obtained at various temperatures in order to determine whether it was possible to correlate the friction signal with desorption of the thiol molecule from the surface.

Simple method for determining the vapor pressure of materials using UV-absorbance spectroscopy.

Accurate thermodynamic parameters of thin films of materials are crucial in understanding their behavior in the nanometer scale. A new and simple method for determining the vapor pressure and thermodynamic properties of nanometer thick films of materials was developed based on UV-absorbance spectroscopy. Well-characterized benzoic acid was used to calibrate the spectrometer and the experimental conditions.

Engineering the microstructure of organic energetic materials.

The initiation sensitivity is highly dependent on void structures within an energetic material. It is technically feasible to modify the initiation sensitivity by lithographically defining the size and distribution of included voids on the micro- and nanoscale. We proposed a method to pattern organic energetic materials using microcontact printing of self-assembled monolayers.

Effect of Zn doping on the sublimation rate of pentaerythritol tetranitrate using atomic force microscopy.

A series of Zn ion-doped pentaerythritol tetranitrate (PETN) nanoislands in the form of thin films were prepared on Si substrates using spin coating. The effect of Zn concentrations on the sublimation energy was investigated by atomic force microscopy (AFM). The pure and Zn-doped nanoislands are imaged by AFM in contact mode at room temperature after annealing isothermally for a given time.

A simple and flexible thin film evaporating device for energetic materials.

A thin film evaporation device has been developed to prepare energetic materials at atmospheric pressure. The device is intuitive, simple, and easy to manipulate. The application of the device is demonstrated for pentaerythritol tetranitrate but can be extended to other explosives and organic materials that have low saturation pressures.

Nondestructive experimental determination of bimaterial rectangular cantilever spring constants in water.

In order to address the issue of spring constant calibration in viscous fluids such as water, a new method is presented that allows for the experimental calibration of bimaterial cantilever spring constants. This method is based on modeling rectangular cantilever beam bending as a function of changing temperature. The temperature change is accomplished by heating water as it flows around the cantilever beams in an enclosed compartment.

Inducing dendrite formation using an atomic force microscope tip.

Atomic force microscope (AFM) tip-induced nucleation, and dendrite growth of vapor deposited PETN films on Si (100) have been investigated at room temperature. The AFM tip induces a change from smooth and flat morphology to islands and dendrites, which is owing to the lowering and vanishing of 2-D nucleation barrier at the tip contact area; this action gives rise to the formation of large islands in the scanned area and dendrite growth along the scanning boundary.

Decoupling functionalization from sensor array assembly using detachable cantilevers.

Cantilevers are useful as sensor devices with high sensitivity and have shown great promise for dense, multianalyte arrays. One of the difficulties has been the fabrication of multianalyte arrays that are capable of the simultaneous detection of a wide range of chemical and biological species. Functionalization procedures for one class of analytes are often incompatible with other classes and cross contamination is a significant concern when ink-jet deposition processes are used.

Effect of surface conjugation chemistry on the sensitivity of microcantilever sensors.

Microcantilever sensors are an offshoot of atomic force microscopy and are useful tools for effectively detecting a target biomolecule. The recognition of the target molecule on the biosensor is based on the physical bending of the microcantilever, which is driven by a specific molecular interaction between the target molecule and the sensor surface. In this study, to enhance the sensitivity of the microcantilever sensor, the sensor surface was modified through a surface conjugation method using self-assembled monolayers (SAMs) and heterobifunctional cross-linkers.