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We have developed a flow cell that allows culturing adherent cells as well as suspended cells in a stable, homogeneous, and low-shear force environment. The device features continuous medium supply and waste exchange. In this paper, a simple and fast protocol for device design, fabrication, and assembly (sealing) based on a poly(dimethylsiloxane) (PMDS)/glass slide hybrid structure is described. The cell culture system performance was monitored, and the effective shear force inside the culture well was also determined. By manipulating the device dimensions and volumetric flow rate, shear stress was controlled during experiments. Cell adhesion, growth, proliferation, and death over long-term culture periods were observed by microscopy. The growth of both endothelial and suspension cells in this device exhibited comparable characteristics to those of traditional approaches. The low-shear culture device significantly reduced shear stress encountered in microfluidic systems, allowing both adherent and suspended cells to be grown in a simple device.

The removal behavior of self-assembled monolayers (SAMs) of thiol molecules on a gold substrate by an NH4OH–H2O2–H2O solution was studied using attenuated total reflectance infrared spectroscopy (ATR-IR) and atomic force microscopy (AFM). Furthermore, the impact of the concentration of NH4OH and H2O2 in the solution and reaction temperature on the SAM removal rate and efficiency was explored. The SAM removal rate and efficiency were significantly influenced by the concentration of NH4OH rather than H2O2. The solution containing the 2 : 1 molar ratio of NH4OH : H2O2 among three different solutions showed the highest removal rate and efficiency in the removal of 11-mercapto-1-undecanol. The increase in the reaction temperature resulted in the enhancement on the SAM removal rate, but it led to the fast delamination of the gold layer. These results may be useful in the regeneration of sensor surfaces relying on gold/thiol chemistry. SCANNING 30: 000–000, 2008. © 2008 Wiley Periodicals, Inc.

Pentaerythritol tetranitrate (PETN) is a very powerful explosive and is generally used in initiators. Changes in the morphology and surface area of aging powders are observed during long term storage, due to coarsening mechanisms (e.g., Ostwald ripening, sintering, sublimation, etc.) These changes in powder properties modify the initiation ability and performance. Various stabilization techniques have been investigated to minimize coarsening in PETN powders. In this report we present our study of changes in morphology between the pure PETN and PETN doped with the ions of iron, calcium, sodium, and zinc. We also carried out studies on the effect of annealing on the morphology of these crystals at the macroscopic and microscopic levels to determine how the different ions modify the crystal.

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering, etc.). In order to alleviate the sublimation of PETN crystals under service conditions, stabilization methods such as thermal cycling and doping with certain impurities during or after the crystallization of PETN have been proposed.

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.

For the first time, we have shown that spin coating and Dip pen nanolithography (DPNTM) are simple methods of preparing energetic materials such as PETN and HMX on the nanoscale, requiring no heating of the energetic material. Nanoscale patterning has been demonstrated by the DPN method while continuous thin films were produced using the spin coating method. Results are presented for preparing continuous PETN thin films of nanometer thickness by the spin coating method and for controlling the architecture of arbitrary nanoscale patterns of PETN and HMX by the DPN method. These methods are simple for patterning energetic materials and can be extended beyond PETN and HMX, opening the door for fundamental studies at the nanoscale.

Pentaerythritol tetranitrate (PETN) is a secondary energetic material generally used in initiators for industrial and government applications. Changes in the morphology and surface area of aging powders have been observed during aging, which can modify the initiability and performance. Here work is presented using two different techniques to determine kinetic and thermodynamic parameters of single crystal PETN. Atomic force microscopy is used for low-temperature analysis, while thermogravimetric analysis is used at higher temperatures. A mechanism is proposed to expand the understanding of coarsening observed in real world PETN.

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. The optical static method of detection is used to measure the deflection of cantilever at the free end. Experimentally determined results are compared to Sader's method and to the Thermotune method most commonly used in cantilever calibrations. Results indicate that the new bimaterial thermal expansion method is accurate within 15%-20% of the actual cantilever spring constant, which is comparable to other nondestructive calibration techniques.

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.