Browsing by Subject "Gas separation"
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Item Characterization of gas separation properties of novel polymer membranes(2015-12) Liu, Qiang. Ph. D.; Freeman, B. D. (Benny D.); Paul, Donald R.; Sanchez, Isaac C; Ellison, Christopher J; Riffle, Judy SPolymers with high permeability (throughput), selectivity (separation efficiency), and long term stability are desired for gas separation applications. This dissertation investigates gas transport properties of two relatively novel polymer membranes: thermally rearranged (TR) polymers and UV-crosslinked poly(arylene ether ketone)s (PAEKs). TR polymers belong to a relatively recent class of materials that, due in part to high free volume and a favorable free volume distribution, have interesting gas separation performance. This work examines the structure-property relationship of several TR isomers, explores the gas transport and mechanical properties of a series of TR copolymers, and investigates the influence of toluene, a model aromatic contaminant in natural gas on pure- and mixed-gas permeation properties of TR polymers. In addition to TR polymers, this thesis also presents the influence of UV irradiation and physical aging on O2 and N2 permeation properties of ultra-thin (~150 nm thick) PAEK films. Gas permeability decreased and selectivity increased with UV irradiation and aging time. Samples irradiated in air have lower permeability coefficients and higher selectivities than samples irradiated in N2. Additionally, physical aging behavior was also influenced by the aging environment and the irradiation wavelength.Item The effect of synthesis route and ortho-position functional group on thermally rearranged polymer thermal and transport properties(2013-05) Sanders, David Finley; Freeman, B. D. (Benny D.); Paul, Donald R.This dissertation discusses the effect of synthesis route and ortho-position group on the thermal and transport properties of thermally rearranged polymers. Thermally rearranged polymers are polybenzoxazoles formed via the solid state rearrangement of ortho-functional polyimides. In this study, polymers were derived from 3,3'-dihydroxy-4,4'-diamino-biphenyl and 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB-6FDA). These HAB-6FDA polymers were synthesized using chemical and thermal imidization, and hydroxyl, acetate, propanoate, or pivalate ortho-position groups were considered. In these polymers, gas permeability increases as a function of conversion for all samples. The polyimide synthesis route does not affect the thermal or transport properties. However, the precursor ortho-position group strongly influences the thermal and transport properties of TR polymers. Additionally, it was determined that an increase in gas diffusivity was the primary cause of increased permeability as a function of thermal rearrangement.Item Physical aging of thin and ultrathin glassy polymer films(2010-05) Rowe, Brandon William; Paul, Donald R.; Freeman, B. D. (Benny D.); Ganesan, Venkat; Eldridge, R B.; Kulkarni, SudhirThis 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.