Daniel J. Burnett

An inorganic–organic proton exchange membrane for fuel cells with a controlled nanoscale pore structure

Proton exchange membrane fuel cells have the potential for applications in energy conversion and energy storage, but their development has been impeded by problems with the membrane electrode assembly. Here, we demonstrate that a silicon-based inorganic-organic membrane offers a number of advantages over Nafion--the membrane widely used as a proton exchange membrane in hydrogen fuel cells--including higher proton conductivity, a lack of volumetric size change, and membrane electrode assembly construction capabilities. Key to achieving these advantages is fabricating a silicon membrane with pores with diameters of approximately 5-7 nm, adding a self-assembled molecular monolayer on the pore surface, and then capping the pores with a layer of porous silica. The silica layer reduces the diameter of the pores and ensures their hydration, resulting in a proton conductivity that is two to three orders of magnitude higher than that of Nafion at low humidity. A membrane electrode assembly constructed with this proton exchange membrane delivered an order of magnitude higher power density than that achieved previously with a dry hydrogen feed and an air-breathing cathode.

Determination of the Surface Energy Distributions of Different Processed Lactose

Particulate interactions between drug and lactose carrier in dry powder inhaler formulations are affected by the heterogenous energy distribution on the surface of the individual compounds. A new method based on Inverse Gas Chromatography at finite concentration is applied to study the energy heterogeneity of untreated, milled, and recrystallized lactose of similar particle size distribution. Energy distributions for the dispersive surface energy and the specific free energy of ethanol are obtained. Milling causes an increase in surface energy due to formation of amorphous regions. Untreated and recrystallized materials have similar surface energies at low surface coverages but show clear differences in energy distribution.

Effect of Processing Route on the Surface Properties of Amorphous Indomethacin Measured by Inverse Gas Chromatography

The aim of this study was to investigate the effect of processing route (i.e., quench cooling and ball milling) on the surface energy heterogeneity and surface chemistry of indomethacin (IMC). Recently developed inverse gas chromatography (IGC) methodology at finite concentrations was employed to determine the surface energy distributions of crystalline, quench cooled and milled IMC samples. Surface properties of crystalline and processed IMC were measurably different as determined by the IGC and other conventional characterization techniques: differential scanning calorimetry and powder X-ray diffraction. Quench cooled IMC was in fully amorphous form. Milled IMC showed no amorphous character by calorimetric or X-ray diffraction studies. It was demonstrated that both processed IMC samples were energetically more active than the crystalline IMC. In particular, milled IMC exhibited a relatively higher dispersive surface energy and higher surface basicity (electron donor capability). This may be attributed to the creation of surface defect sites or exposure of higher energy crystal facets during the milling process. This study confirms that processing route has notable influence on the surface energy distribution and surface acid–base character. IGC was demonstrated as a powerful technique for investigating surface properties of real-world, heterogeneous pharmaceutical materials.

Quantification of surface amorphous content using dispersive surface energy: the concept of effective amorphous surface area.

We investigate the use of dispersive surface energy in quantifying surface amorphous content, and the concept of effective amorphous surface area is introduced. An equation is introduced employing the linear combination of surface area normalized square root dispersive surface energy terms. This equation is effective in generating calibration curves when crystalline and amorphous references are used. Inverse gas chromatography is used to generate dispersive surface energy values. Two systems are investigated, and in both cases surface energy data collected for physical mixture samples comprised of amorphous and crystalline references fits the predicted response with good accuracy. Surface amorphous content of processed lactose samples is quantified using the calibration curve, and interpreted within the context of effective amorphous surface area. Data for bulk amorphous content is also utilized to generate a thorough picture of how disorder is distributed throughout the particle. An approach to quantifying surface amorphous content using dispersive surface energy is presented. Quantification is achieved by equating results to an effective amorphous surface area based on reference crystalline, and amorphous materials.

Interaction of water with three granular biopesticide formulations.

Two obstacles for biopesticide commercialization, long shelf life and reliable efficacy, are both affected by moisture availability. Three biopesticide delivery systems, TRE-G, PEC-G, and PESTA, were analyzed by dynamic vapor sorption analysis. The objective was to investigate the moisture sorption profile of each system in air at 25 degrees C and a relative humidity (RH) ranging from 0 to 90%. The formulations sorbed up to 12.7% moisture. In rehydrating from 0.00 to 90% RH, TRE-G and PEC-G were >or=63% and >or=58% faster than Pesta, respectively. In losing moisture from 90 to 0.00% RH, Pesta was 3.4 and 2.3 times slower than TRE-G and PEC-G, respectively. The GAB model was inadequate for describing moisture sorption, but the Young and Nelson model showed good correlation (r > 0.990) for all three formulations. Moisture distribution for all formulations was obtained. The implications of the findings as they relate to shelf life and dew period requirements of biopesticides are discussed.