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This research effort investigated the influence of confinement on the physical aging behavior of thin and ultrathin glassy polymer membranes. Membrane permeability changes with time due to physical aging, and for reasons not completely understood, the rate of permeability change can become orders of magnitude faster in films thinner than one micron. Special experimental techniques were developed to enable the study of free standing, ultrathin glassy polymer films using gas permeability measurements. The gas transport properties and physical aging behavior of free-standing glassy polysulfone (PSF) and Matrimid® films from 18-550 nm thick are presented. Physical aging persists in glassy films approaching the length scale of individual polymer coils. The membranes exhibited significant reductions in gas permeability and increases in selectivity with aging time. Additionally, the influence of physical aging on the free volume profile in thin PSF films was investigated using variable energy positron annihilation lifetimespectroscopy (PALS). The films exhibited decreasing o-Ps lifetime during physical aging, while o-Ps intensity remained constant. The o-Ps lifetime was reduced at lower implantation energies, indicating smaller free volume elements near the film surface. Thin films aged dramatically faster than bulk PSF and the PALS results agree favorably to behavior tracked by gas permeability measurements. The physical aging behavior of ultrathin films with different previous histories was also studied. The state of these materials was modulated by various conditioning treatments. Regardless of the previous history, the nature of the aging response was consistent with the aging behavior of an untreated film that was freshly quenched from above Tg, i.e., permeability decreased and pure gas selectivity increased with aging time. However, the extent of aging-induced changes in transport properties of these materials depended strongly on previous history. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced Tg in ultrathin films, which allows them to reach a lower free volume state more quickly than bulk material. The Struik physical aging model was extended to account for the influence of film thickness on aging, and was shown to accurately describe the experimental data. / text

This study deals with polyvinylamine (PVAm)-poly(vinyl alcohol) (PVA) based composite membranes incorporated with carbon nanotubes (CNTs) and molecular amines (e.g., piperazine (PZ), triethanolamine (TEA), N-methyldiethanolamine (MDEA), PZ/TEA and PZ/MDEA blends, diethylenetriamine (DETA) and triethylenetetramine (TETA)) for CO2 separation, solvent dehydration by pervaporation, and hydrogen purification. The effects of the parameters involved in the procedure of membrane formation and operating conditions on the membrane performance were investigated. Composite membranes comprising of a skin layer of PVAm-PVA incorporated with CNTs and a microporous polysulfone substrate were developed for CO2 separation from flue gas and dehydration of ethylene glycol by pervaporation. The membranes were characterized with Fourier transform infrared (FTIR), Raman spectroscopy, X-ray diffraction (XRD), contact angle measurement and water sorption uptake, using dense films of PVAm-PVA/CNTs, to determine the effects of CNTs on the intermolecular interactions, degree of crystallinity, surface hydrophilicity, and degrees of swelling of the membranes. For CO2/N2 separation, adding CNTs in the membrane was shown to enhance CO2 permeance while retaining a similar CO2/N2 selectivity; a CO2 permeance of 18.5 GPU and a CO2/N2 ideal selectivity of 64 were obtained at 0.6 MPa feed pressure. For pervaporative dehydration of ethylene glycol, the incorporation of CNTs into the membrane was shown to increase both the permeation flux and separation factor, and at 70??? a permeation flux of 146 g/(m2.h) and a separation factor of 1160 were achieved at 1 wt% water in feed using a PVAm-PVA/CNT composite membrane containing 2 wt% MWNTs. Novel facilitated transport membranes containing both PVAm as fixed carriers and various molecular amines as mobile carriers were fabricated and used for CO2 separation from N2 and H2, as well as CO2 separation from ethanol fermentation off gas. For membranes containing a single amine (i.e., PZ, DETA or TETA), the CO2 permeance increased with an increase in the amine content in the membrane until the amine content is sufficiently high, beyond which a further increase in the amine content would decrease the membrane performance. The facilitation in CO2 transport was more significant with membranes containing mixed amines (e.g., PZ/TEA and PZ/MDEA). Among all the molecular amines tested, TETA was shown to be most effective in facilitating CO2 transport in terms of CO2/N2 permselectivity. Using a PVAm-PVA/TETA composite membrane with a TETA to polymer (i.e., PVAm plus PVA) mass ratio of 150/100, a CO2 permeance of 22.6 GPU and a CO2/N2 selectivity of 86.5 were obtained at 0.6 MPa feed pressure for the removal of CO2 from flue gas, a CO2 permeance of 23.3 GPU and a CO2/H2 selectivity of 28.5 were obtained at 0.6 MPa feed pressure for CO2 separation from H2, a water vapor permeance of 16700 GPU was obtained at 25??? and 2.5 mol% water vapor concentration in the feed for dehydration of ethanol fermentation off gas.

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Feb. 24, 2009). Includes bibliographical references (p. 91-93).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 242-260). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 186-197). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 221-227). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Gary T. Rochelle and William J. Koros. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: William J. Koros and Donald R. Paul. Vita. Includes bibliographical references.