Not available / text

Not available / text

There is significant interest in understanding and exploiting the extraordinary property enhancements of polymers, enabled by adding small concentrations of nanoparticles to polymer hosts to create polymer nanocomposites (PNCs). Thin film PNCs hold potential for novel technological applications in areas such as optoelectronics or photovoltaic devices. One of the key challenges that limits the potential of PNC-based technologies is the control of nanofiller dispersion throughout the matrix. This requires a fundamental understanding of the energetic interactions that affect dispersion. Thin film PNCs pose a greater challenge than bulk PNCs, largely because interfacial interactions become increasingly important as the material is confined. It is equally important to find effective processing schemes that promote nanofiller dispersion in a manner that can be readily scalable for industrial operations. Accordingly, the last few years have seen an upsurge in processing schemes involving supercritical solvents, due in part to their tunable solvent strength. To this end, our research is aimed at gaining control of nanoparticle dispersion within thin film hosts using supercritical CO₂ (scCO₂) as a processing aid. This research examined a series of related problems. For the first project, we investigated the effects of scCO₂ sorption on the structural stability and kinetics of destabilization of homopolymer films. We showed that the films are metastable under these conditions, and the barrier to nucleation is larger than that encountered in air/vaccum. We also examined the issue of nanofiller dispersion within homopolymer thin films. In a model athermal mixture, polystyrene-coated gold nanoparticles in polystyrene hosts, interfacial segregation was generally observed, and was shown to be a function of the wetting characteristics of the brush-matrix interface and the ratio of the size of the particles to the unperturbed dimensions of the host chains. In a separate system, we show how scCO₂ can serve to prevent coarsening, which is ubiquitous in air/vacuum environments at elevated temperatures, for these nanofillers. Finally, we made nanocomposite micellar structures from block copolymers, with a fluorinated block. Gold nanoparticles were sequestered within the discontinuous domain. We then showed how scCO₂ could be used to invert the structure, placing the nanoparticles in the continuous phase.

A large-scale pilot plant (0.43 m ID) was extensively modified and converted into an absorber/stripper system to demonstrate CO₂ capture technology using aqueous piperazine promoted potassium carbonate for coalfired power plants. Four pilot plant campaigns were completed. Three campaigns were conducted using 5 m K⁺/2.5 m PZ and 6.4 m K⁺/1.6 m PZ. Flexipac 1Y and Flexipac AQ Style 20 structured packing were used in the absorber. The stripper was tested with 14 sieve trays, IMTP #40 random packing, and Flexipac AQ Style 20 packing. Monoethanolamine (7 m) was tested in the third campaign to establish a base case. An approximate rate analysis showed that 5 m K⁺/2.5 m PZ is two times faster than 7 m MEA and three times faster than 6.4 m K⁺/1.6 m PZ. The location of the temperature bulge moves from the top of the column to bottom as the liquid to gas flow rate ratio is increased. Foaming occurred in the absorber in the first two campaigns and occurred in the stripper in the fourth campaign. Data from the pilot plant was used to develop a K⁺/PZ absorber model in Aspen Plus® RateSep[trademark]. The Hilliard (2005) Aspen Plus® VLE model and the kinetics developed by Cullinane (2005) were incorporated in the model. Data-Fit was simultaneously used to reconcile pilot plant data and perform a regression of the interfacial area and heat loss parameters for the RateSep[trademark] absorber model. The lean loading for the pilot plant data was shifted down by 10% to account for a discrepancy with the Cullinane vapor-liquid equilibrium data. The Data-Fit results showed that the average interfacial area for Flexipac 1Y was 80% of the value measure by the air-water column. The average interfacial area for Flexipac AQ Style 20 for 5 m K⁺/2.5 m PZ was 56% of the air-water measurement. The CO₂ heat of absorption may not have been adequately predicted by the RateSep[trademark] absorber model because the regressed values of heat loss were consistent with forced convection.

The mystery surrounding high concentrations of Cr(III) in plants has been uncovered. It is attributed to the presence of low molecular weight organic acids (LMWOA) in soil in which the plants are growing. Apart from that, the factors influencing solubility of Cr(VI) in soil have also been investigated. It was found that the solubility of Cr(VI) species is governed by the presence of CO3 2− ions in a soil solution that resulted when atmospheric CO2 dissolves in soil–water. Concentrations of Cr(VI) and Cr(III) were determined in plants, collected on unpolluted soils in different geographical areas. It was found that the concentration of Cr(VI) in plants correlated with the soluble fraction of Cr(VI) in soil, while Cr(III) concentration in plants is limited by concentration LMWOA in soil. It can therefore be concluded that the high level of Cr(III) in plants is also due to the direct absorptions of the species from soil rich in organic acids.

No description available.

No description available.

No description available.

The exchange of carbon dioxide between the atmosphere and the polar caps on Mars creates a seasonal cycle of growth and retreat of the polar caps. As the major component of the Martian atmosphere, CO2 condenses in the polar regions of the planet during the winter seasons and precipitates as CO2 frost. It then sublimes during the spring and summer seasons in response to solar radiation. Through natural radioactivity or when exposed to cosmic rays, elements in the Martian near-subsurface (uppermost meter) emit gamma rays with distinct, characteristic energies. The Gamma Ray Spectrometer (GRS) onboard the 2001 Mars Odyssey satellite is used to measure the gamma rays coming from the Martian regolith to calculate elemental distributions, abundances, and temporal variations in the gamma ray flux. Changes in the CO2 frost over time can be quantified by observing attenuation effects of H (2223 keV hydrogen) and 40K (1461 keV potassium) gamma ray signals transmitted through various depths of polar CO2 overburden throughout the Martian seasons.Conclusions are drawn about the spatial extent, column density, and mass of Mars' seasonal polar caps as a function of time utilizing GRS data. Columnar thickness and mass results are discussed and plotted for latitudes including +/-60 degrees and poleward. GRS observations are compared to predictions from the NASA Ames Research Center Mars General Circulation Model (ARC GCM) and to similar experimental results from the Mars Odyssey High Energy Neutron Detector (HEND) and the Neutron Spectrometer (NS). Models for north and south polar atmosphere and regolith distributions are incorporated, and the results indicate that the assumption of a 100% H2O-ice residual cap underlying the seasonal frost in the north is accurate. The GRS CO2 frost observations are in good agreement with the other studies mentioned, in particular for the timing of the beginning of frost deposition to the complete sublimation of surface CO2 back into the atmosphere. The total amount of condensed CO2 mass derived from GRS data is on the order of 6.0 x 10^15 kg and verifies previous reports that ~25% of the total Martian exchangeable-CO2 reservoir participates in the ground-atmosphere cycle.

La Tesis està dividida en dues parts, en la primera part es descriu l’ús del diòxid de carboni com a dissolvent alternatiu en la reacció catalitzada amb complexos catiònics i dicatiònics de pal•ladi en la copolimerització de CO/vinyl arens comparant l’activitat catalítica amb el medi convencional (2,2,2-trifluoroetanol). S’ha estudiat el mecanisme d’iniciació i terminació de la reacció de copolimerització mitjançant l’estudi per MALDI-TOF dels copolímers. La química de coordinació del lligand hibrid bidentat P,N 2-(2’-pyridyl)-4,6-diphenylphosphinine (L4) amb Pd(II), Pt(II) i Rh(I) han estat investigats. La reactivitat dels complexos de Pd(II) i Pt(II) amb alcohols (quirals) i amines (quirals) a elevada temperatura, dóna lloc al complex [MCl2[L4H•XR] (XR = OR or NR1R2). En la segona part de la Tesis es descriu l’ús del diòxid de carboni com a matèria prima en la reacció de copolimerització de CO2 amb epòxid catalitzada amb complexos de zinc (II). L’efecte dels diferents substituents dels lligands aminoalcohols en front la productivitat i la selectivitat pel policarbonat es va estudiar en dita reacció. Per altra banda, es van sintetitzar i caracteritzar nous complexos de Zn(II) amb lligands N,N,O-tridentats i es van obtenir resultats catalítics preliminars. / The Thesis is divided in two parts, in the first part is described the use of carbon dioxide as green solvent in dicationic and cationic palladium catalysed CO/vinyl arenes copolymerisation comparing the catalytic activity with conventional media (2,2,2-trifluoroethanol). The initiation and termination mechanism of the copolymerisation reaction was studied by MALDI-TOF analysis of the copolymers. The coordination chemistry of the bidentate P,N hybrid ligand 2-(2’-pyridyl)-4,6-diphenylphosphinine (L4) towards Pd(II), Pt(II) and Rh(I) was investigated. Both Pd(II) and Pt(II) complexes reacted with (chiral) alcohols and (chiral) amines at the P=C double bond at elevated temperature, leading to the corresponding products [MCl2[L4H•XR] (XR = OR or NR1R2). In the second part is described the use of carbon dioxide as C1 building block in zinc (II) catalysed CO2/epoxides copolymerisation. The effect in the productivity and polycarbonate selectivity of the different amino-alcohol substituents were studied. Moreover, new zinc (II) Schiff base complexes were synthesized; characterized and preliminary catalytic studies were obtained.