Don H. Rasmussen

Effect of Solute on Ice-Solution Interfacial Free Energy; Calculation from Measured Homogeneous Nucleation Temperatures

Among the forms of the water polymer interface of interest to low temperature scientists one distinguishes in particular the common surfaces separating ice from solid polymer and ice from aqueous polymer solution. The ice — solid polymer interface has been the subject of considerable attention; it was, for example, discussed at the Sapporo Conference on the Physics of Snow and Ice in 1966 /1/ and was the subject of a symposium chaired by Dr. H. H. G. Jellinek in 1967 /2/. Studies on the ice — aqueous solution interface have, in contrast, been limited largely to the interpretation of growth rate measurements in dilute salt solutions /3/, where the physical characteristics of the solution dominate the contribution from the surface effects.

Mechanisms of anodic bonding of silicon to pyrex glass

The mechanisms of formation of anodic bonds between glasses and metals are examined. The process is found to be an electrochemical analog to thermal glass-to-metal seals, where the metal surface is oxidized into the glass due to the development of large electric fields across the anodic depletion layer. The current vs. time transient at constant voltage contains a significant amount of information regarding the process mechanisms, which are predominantly electrochemical.<<ETX>>

Interactions in the Water-Polyvinylpyrrolidone System at Low Temperatures

Great interest has attached to the hydration of macromolecular species and to the state of water molecules in hydrophilic polymer systems in particular. Bull /1/ and Hoover and Mellon /2/ reported the sorption of water by cellulose, cellulose acetate, nylon, and numerous proteins, applying equations developed originally to describe the binding of monatomic gases and small molecules to free surfaces. Bull determined the method of Brunauer, Emmett and Teller /3/ to suffice at 25 and 40°C. from 0.05 to 0.50 water activity (denoted hereafter by the symbol ‘aW’). Hoover and Mellon applied Bradley’s isotherm /4,5/ very successfully throughout the range of aW’ s (0.06 to 0.93) encompassed in their studies. Bull, and Hoover and Mellon each determined that water became attached to certain sites on the macromolecules, also that additional water molecules became attached to the first to form layer-like structures.

The Impact of Deliquescence and pH on Cr Speciation in Ambient PM Samples

The 2 chromium oxidation states found in ambient atmospheric particulate matter (PM) are trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium. Cr(III) is a trace element essential for the proper function of living organisms. However, Cr(VI) is toxic and exposure to Cr(VI) may lead to cancer, nasal damage, asthma, bronchitis, pneumonitis, inflammation, dermatitis, and skin allergies. Therefore, it is important to accurately discriminate between these 2 species in atmospheric PM samples. This work focuses on the effect of deliquescence and pH on chromium speciation in filter samples of airborne PM collected in the northeastern USA. The deliquescence relative humidity (DRH) and liquid water mass content determined for the ambient particle samples are in good agreement with previously reported values for ammonium sulfate and ammonium nitrate suggesting that these 2 salts control the hygroscopic properties of the ambient particles in the northeastern USA. The loss of Cr(VI) increases significantly up to 85% at acidic pH as Cr(III) becomes more stable. Under basic pH conditions, deliquescence increases the loss of Cr(VI) such that up to 33% reduction was observed at 96% relative humidity (RH). No statistically significant difference was observed for Cr(VI) and Cr(III) interconversion over a range of ambient PM mass. Because of the effect of deliquescence on chromium speciation at basic pH, a new design criterion for Cr(VI) samplers can be defined to preserve the collected Cr(VI). DRH of sodium bicarbonate, K2Cr2O7, and Cr(NO3)3 was found to be 91%, 94%, and 52%, respectively. Copyright 2012 American Association for Aerosol Research

Comparison of Experimental and Theoretical Heterogeneous Nucleation on Ultrafine Carbon Particles.

Using a modified turbulent mixing CNC, the heterogeneous nucleation of different compounds (working fluids) on nanometer sized carbon particles was examined. The working fluids were dibutyl phthalate, octadecane, octadecanol, and octadecanoic acid. Based on the particle size distributions measured with a scanning mobility particle sizer system, nucleation and consequent growth were examined with respect to different temperature and vapor pressure for each working fluid. Nucleation rates for all conditions were calculated from the fitted size distribution data by subtracting the residual nonactivated particle concentration for each condition. Experimental nucleation rates were compared to the calculated ones based on Fletchers heterogeneous nucleation theory. This theory matches well with the experiments with octadecanol and octadecanoic acid, and at high supersaturation ratios for dibutyl phthalate. However, the theory shows discrepancies with the observed phenomena at low supersaturation for dibutyl phthalate, and especially for octadecane. Several possible hypotheses for the discrepancies and observed particle growth are discussed.

Relationship of phase diagrams and surfaces of new phase nucleation rates

Experimental and theoretical investigations of vapor nucleation began about 100 years ago. Until the 1980s, experiments generally measured only critical supersaturation values. Since then, measurement procedures have substantially improved and nucleation rates can now be measured as a function of temperature, vapor activities, and pressure with high accuracy. Nucleation theory has made obvious progress, but the understanding of nucleation phenomenon is far from complete. New approaches to conceptualizing nucleation are necessary in order to identify possible new directions for further improvement of nucleation theory. One such approach is the analysis of the topology of nucleation rate surfaces. The creation of a nucleation rate surface is based on knowledge of phase equilibrium diagrams, limited experimental nucleation results, and a few plausible assumptions. In this article, the surfaces of the nucleation rates as a function of pressure or activity for single and binary systems for nucleation from meta...

Dynamic surface tension and classical nucleation theory

Regular solution theory is used to develop the concentration dependence for both the equilibrium and dynamic surface tension of water–alcohol binary solutions. The equilibrium surface tensions of methanol–water, ethanol–water, and n‐propanol–water binary solutions are used to fit the parameters of the theory and the dynamic surface tension is calculated. The dynamic surface tension compares favorably with the surface tension which fits classical nucleation theory vs composition at a nucleation rate of one nuclei per cubic centimeter per second.

Water Clusters in Amorphous Pharmaceuticals

Amorphous materials, although lacking the long-range translational and rotational order of crystalline and liquid crystalline materials, possess certain local (short-range) structure. This paper reviews the distribution of one particular component present in all amorphous pharmaceuticals, that is, water. Based on the current understanding of the structure of water, water molecules can exist in either unclustered form or as aggregates (clusters) of different sizes and geometries. Water clusters are reported in a range of amorphous systems including carbohydrates and their aqueous solutions, synthetic polymers, and proteins. Evidence of water clustering is obtained by various methods that include neutron and X-ray scattering, molecular dynamics simulation, water sorption isotherm, concentration dependence of the calorimetric Tg , dielectric relaxation, and nuclear magnetic resonance. A review of the published data suggests that clustering depends on water concentration, with unclustered water molecules existing at low water contents, whereas clusters form at intermediate water contents. The transition from water clusters to unclustered water molecules can be expected to change water dependence of pharmaceutical properties, such as rates of degradation. We conclude that a mechanistic understanding of the impact of water on the stability of amorphous pharmaceuticals would require systematic studies of water distribution and clustering, while such investigations are lacking.

Improved atmospheric sampling of hexavalent chromium

Hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) are the primary chromium oxidation states found in ambient atmospheric particulate matter. While Cr(III) is relatively nontoxic, Cr(VI) is toxic and exposure to Cr(VI) may lead to cancer, nasal damage, asthma, bronchitis, and pneumonitis. Accurate measurement of the ambient Cr(VI) concentrations is an environmental challenge since Cr(VI) can be reduced to Cr(III) and vice versa during sampling. In the present study, a new Cr(VI) sampler (Clarkson sampler) was designed, constructed, and field tested to improve the sampling of Cr(VI) in ambient air. The new Clarkson Cr(VI) sampler was based on the concept that deliquescence during sampling leads to aqueous phase reactions. Thus, the relative humidity of the sampled air was reduced below the deliquescence relative humidity (DRH) of the ambient particles. The new sampler was operated to collect total suspended particles (TSP), and compared side-by-side with the current National Air Toxics Trends Stations (NATTS) Cr(VI) sampler that is utilized in the U.S. Environmental Protection Agency (EPA) air toxics monitoring program. Side-by-side field testing of the samplers occurred in Elizabeth, NJ, during the winter and summer of 2012. The average recovery values of Cr(VI) spikes after 24-hr sampling intervals during summer and winter sampling were 57 and 72%, respectively, for the Clarkson sampler, while the corresponding average values for NATTS samplers were 46% for both summer and winter sampling, respectively. Preventing the ambient aerosol collected on the filters from deliquescing is a key to improving the sampling of Cr(VI). Implications: This study describes a sampler that provides cooling and drying of the particle collection filter by reducing the ambient air relative humidity to below deliquescence relative humidity of ambient particles. This Clarkson Cr(VI) sampler improved the measurement of ambient Cr(VI) concentration. It showed higher Cr(VI) recovery during field tests (71.8 ± 4.9% in winter and 57.1 ± 0.2 % in summer) compared to the current EPA Cr(VI) sampler (46.2 ± 10.8% in winter and 46.0 ± 1.6% in summer) that is employed in the National Air Toxics Trends Stations (NATTS) monitoring program. Supplemental Materials: Supplemental materials are available for this paper. Go to the publishers online edition of the Journal of the Air & Waste Management Association.

Electrodeposition of CuGaSe2 from Thiocyanate-Containing Electrolytes

� as a complexing agent to cathodically shift the reduction potential of CuII. In the presence of thiocyanate, the peak reduction currents for CuII and GaIII during cyclic voltammetry occur at potentials that differ by only 80 mV, even though the standard reduction potentials of the uncom- plexed species differ by about 870 mV. Stoichiometric CuGaSe2 deposits are obtained by the induced codeposition mechanism at �300 mV vs SCE and pH 2.75 from electrolytes with Cu:Ga ratios ranging from 0.5 to 1.5. The stoichiometry is controlled by the thermodynamic driving force associated with stable compound formation, as illustrated by the anodically shifted reduction peak obtained in cyclic voltammograms of electrolytes containing all three elemental species. Oxygen incorporation into the electrode- posit is observed, because electrodeposition of stoichiometric CuGaSe2 appears to be immediately followed by Ga oxidation. Methods for removing oxygen from the electrodeposited film are discussed.