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Donald R Paul - One of the best experts on this subject based on the ideXlab platform.
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enthalpy recovery and structural relaxation in layered Glassy Polymer films
Polymer, 2012Co-Authors: Thomas M Murphy, Deepak Langhe, Michael Ponting, Eric Baer, Benny D Freeman, Donald R PaulAbstract:Abstract Recent studies of physical aging in confined Polymer glasses have revealed that aging behavior in confinement often differs from bulk behavior. This study used DSC to characterize physical aging and structural relaxation in bulk polysulfone (PSF) and co-extruded multilayered films of PSF and an olefin block coPolymer (OBC) that have average PSF layer thicknesses of 640 nm, 260 nm, and 185 nm. The films were aged isothermally at 170 °C, and the recovered enthalpy upon reheating was measured over time. The films with 640 nm and 260 nm PSF layers had aging rates very similar to that of bulk PSF, while the film with 185 nm PSF layers had an aging rate slightly greater than the bulk value. The cooling rate dependence of the limiting fictive temperature (Tf′) in multilayered and bulk PSF samples was also characterized. Values of Tf′ were similar for all films at each cooling rate. The results of this work are in general agreement with our previous gas permeation aging study of multilayered PSF films aged at 35 °C, in which the effect of layer thickness on aging behavior was minimal. This stands in contrast to studies with thin, freestanding PSF films, which exhibit accelerated aging relative to bulk and have aging rates that depend strongly on film thickness.
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carbon dioxide sorption and plasticization of thin Glassy Polymer films tracked by optical methods
Macromolecules, 2012Co-Authors: Norman R Horn, Donald R PaulAbstract:Our previous publications have demonstrated that thin Glassy Polymer films respond to highly sorbing penetrants, such as CO2, quite differently than thick films. These studies focused on CO2 permeation behavior and revealed that, for thin films, CO2 permeability at constant CO2 pressure goes through a maximum followed by a continual decrease in permeability owing to physical aging. So far, thick and thin Glassy Polymer films have been compared in the context of permeability, but lack of substantial means of obtaining thin film sorption data has prevented adequate comparison of thick and thin films in the context of gas solubility. In this paper, spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO2 sorption capacity for thin Glassy Polymer films. This allows a more comprehensive look at CO2 permeability, sorption, and diffusivity as a function of both CO2 pressure and exposure time. The evidence reported here suggests that thin film sorption behavior is substantially diffe...
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physical aging of layered Glassy Polymer films via gas permeability tracking
Polymer, 2011Co-Authors: Thomas M Murphy, Deepak Langhe, Michael Ponting, Eric Baer, Benny D Freeman, Donald R PaulAbstract:The physical aging of Polymers in confined environments has been an area of intensive study in recent times. The rate of physical aging in thin films of many Polymers used in gas separation membranes is dependent on film thickness and accelerated relative to bulk. In this study, the physical aging of Polymer films with alternating Glassy polysulfone and rubbery polyolefin layers was monitored by measuring the gas permeability of O2 and N2 as a function of aging time at 35 � C. The alternating layer structures were formed by a melt co-extrusion process. The polysulfone layers have thicknesses ranging from 185 to 400 nm, and the overall thicknesses of the films are on the order of 80e120 mm. The aging of freestanding thin films of polysulfone is rapid and exhibits clear thickness dependence, whereas the aging of multilayered films was observed to be similar to bulk and showed no dependence on layer thickness. At 1000 h of aging time, a 400 nm freestanding PSF film decreased in O2 permeability by 35%, whereas on average the bulk and multilayered films only experienced a decline of 10e15%. A slight increase in O2/N2 selectivity for the multilayered films was observed over the course of aging.
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carbon dioxide plasticization of thin Glassy Polymer films
Polymer, 2011Co-Authors: Norman R Horn, Donald R PaulAbstract:Abstract We have demonstrated in previous studies that thin Glassy Polymer films exhibit complex responses to highly sorbing penetrants, such as CO 2 , relative to their thick film counterparts. In this paper, we apply similar experiments to two new Polymers, including a polysulfone made from bisphenol A (PSF), and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and compare their responses to Matrimid ® to understand better CO 2 plasticization behavior of these materials when in thin film form. As expected, the extent of plasticization response tracks with CO 2 solubility; CO 2 diffusivity may also be an important factor at shorter exposure times. Experiments at longer CO 2 exposure times revealed that each Polymer experiences the permeability maximum observed in our previous work as well. However, Polymers that are not as highly sorbing to CO 2 , like polysulfone, may not at some conditions exhibit a distinct permeability maximum but will still decrease in permeability after a long period of CO 2 exposure owing to physical aging.
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carbon dioxide plasticization and conditioning effects in thick vs thin Glassy Polymer films
Polymer, 2011Co-Authors: Norman R Horn, Donald R PaulAbstract:Abstract Recent studies have shown that thin Glassy Polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the plasticization and conditioning responses of thin Glassy films in the presence of highly-sorbing penetrants such as CO2. In this paper, a carefully designed systematic study explores the effect of thickness on the CO2 plasticization and conditioning phenomena in Matrimid®, a polyimide commonly used in commercial gas separation membranes. Thin films are found to be more sensitive than thick films to CO2 exposure, undergoing more extensive and rapid plasticization at any pressure. The response of Glassy Polymers films to CO2 is not only dependent on thickness, but also on aging time, CO2 pressure, exposure time, and prior history. Finally, thin films experiencing constant CO2 exposure for longer periods of time exhibit an initial large increase in CO2 permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored.
Yongjiang Huang - One of the best experts on this subject based on the ideXlab platform.
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Effect of Film Thickness on the Gas-Permeation Characteristics of Glassy Polymer Membranes
Industrial & Engineering Chemistry Research, 2007Co-Authors: Yongjiang Huang, Donald R PaulAbstract:Films made from three Glassy Polymerspolysulfone, poly(2,6-dimethyl-1,4-phenylene oxide), and a commercial polyimide known as Matrimidwere prepared in thicknesses ranging from 0.4 μm to 60 μm, and their permeabilities to oxygen, nitrogen, and methane were monitored for more than a year. These films exhibited substantial decreases in permeability with time, because of volume relaxation that is due to physical aging, which is a reversible process. The observed permeability coefficients were originally greater than the literature values for thick, or so-called “bulk” films, but eventually decreased well below these values. The rate of the aging effect becomes greater the thinner the film. The implications of this observation for practical membrane gas separation processes and the selection of membrane materials based on thick film data are discussed.
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physical aging of thin Glassy Polymer films free volume interpretation
Journal of Membrane Science, 2006Co-Authors: Yongjiang Huang, Xiaoyan Wang, Donald R PaulAbstract:Abstract Previous studies have documented the dramatic effects of film thickness, at least compared to the bulk state, and the more modest effects of aging temperature and Polymer structure on physical aging of thin Glassy Polymer films. In this paper, these results are interpreted in terms of the free volume calculated from the refractive index, determined by ellipsometry, using the Lorentz–Lorenz equation. The relative progress of aging towards the final equilibrium state was determined using this approach. The free volume data were fitted to the Struik model for the self-retarding volume contraction on aging to obtain the thickness and temperature dependent parameters. The gas permeability versus aging time is related to the free volume computed from the refractive index. The effect of prior history on the aging of thin Glassy Polymer films was briefly explored.
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physical aging of thin Glassy Polymer films monitored by optical properties
Macromolecules, 2006Co-Authors: Yongjiang Huang, Donald R PaulAbstract:The change in refractive index of thin films formed from three Glassy Polymers, polysulfone, a polyimide, and poly(2,6-dimethyl-1,4-phenylene oxide), measured by ellipsometry was used to track their physical aging. These thin films with thicknesses less than 1 μm were aged for up to 6000 h at 35 °C. A pronounced aging response via refractive index change, attributed to the densification of the Glassy Polymers, was observed for each film. The Lorentz−Lorenz equation was used to relate changes in refractive index to densification, or volume relaxation, with aging time. The volumetric aging rate was shown to be dependent on the Polymer structure and the film thickness. These thin films age at rates orders of magnitude more rapid than expected for bulk or thick films.
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experimental methods for tracking physical aging of thin Glassy Polymer films by gas permeation
Journal of Membrane Science, 2004Co-Authors: Yongjiang Huang, Donald R PaulAbstract:Abstract This paper describes methodologies that have been developed for studying the physical aging of free-standing thin Polymer films and its effect on gas permeability. Both solution casting and spin coating methods were used to obtain thin polysulfone films having thicknesses in the range of 400–1000 nm. Ellipsometry has been employed to determine the thicknesses of these thin films. A thin wire frame was used to hold the thin free-standing films while heating above Tg to relax molecular orientation and to erase the ambiguous thermal history resulting from solution casting. The film underwent a significant thickness change during heating above Tg as the Polymer chains relaxed. By using the method of this study, the reproducibility of gas permeability change during physical aging was demonstrated as well as the thermoreversibility of physical aging. Comparison of the results obtained by using different methods to support the thin film during heating illustrated the preference for the free-standing scheme developed in this study.
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physical aging of thin Glassy Polymer films monitored by gas permeability
Polymer, 2004Co-Authors: Yongjiang Huang, Donald R PaulAbstract:Abstract The physical aging at 35 °C of three Glassy Polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O 2 , N 2 , and CH 4 , for over 200 days. Several techniques were used to accurately determine the thickness of films (∼400 nm–62 μm) in order to obtain absolute permeability coefficients and to study the effects of film thickness on the rate of physical aging. Each film was heated above the Polymer T g to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in Polymer free volume, was observed at temperatures more than 150 °C below T g for thin films of each Polymer compared to what is observed for the bulk Polymers. The films with thicknesses of approximately 400 nm of the three Polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14–15% increase in O 2 /N 2 selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on physical aging were examined briefly.
Joseph L Keddie - One of the best experts on this subject based on the ideXlab platform.
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thickness dependence of structural relaxation in spin cast Glassy Polymer thin films
Physical Review E, 2004Co-Authors: Hugh Richardson, I Lopezgarcia, Michele Sferrazza, Joseph L KeddieAbstract:The isothermal structural relaxation of Glassy, spin-cast Polymer thin films has been investigated. Specifically, the thickness h of freshly cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, It was found to be greater than the equilibrium thickness h(infinity), which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h. (referred to as delta(0)) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h(infinity), and delta(0) is small, whereas in thick films (>500 nm), a plateau value of delta(0) of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of) on thickness is observed regardless of the substrate, Polymer molecular weight, or angular velocity during spin casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the Polymer during the deposition process.
Matthew R Hill - One of the best experts on this subject based on the ideXlab platform.
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control of physical aging in super Glassy Polymer mixed matrix membranes
Accounts of Chemical Research, 2020Co-Authors: Matthew R Hill, Kristina Konstas, Stefan J D Smith, Ammara AkramAbstract:ConspectusSince the discovery of Polymers of intrinsic microporosity (PIMs) in 2004, the fast size-selective interconnected pore cavities of the Polymers have caused the upper bound of membrane per...
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ending aging in super Glassy Polymer membranes
Angewandte Chemie, 2014Co-Authors: Phuc Tien Nguyen, Matthew R Hill, Aaron W Thornton, Kristina Konstas, Cara M Doherty, Roger J Mulder, Laure Bourgeois, David Sprouster, James Sullivan, Timothy J BastowAbstract:Aging in super Glassy Polymers such as poly(trime- thylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and Polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas- separation membranes. While super Glassy Polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super Glassy Polymers through absorbing a portion of the Polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super Glassy Polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super Glassy Polymers to be revisited for commercial application in gas separations.
Michele Sferrazza - One of the best experts on this subject based on the ideXlab platform.
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thickness dependence of structural relaxation in spin cast Glassy Polymer thin films
Physical Review E, 2004Co-Authors: Hugh Richardson, I Lopezgarcia, Michele Sferrazza, Joseph L KeddieAbstract:The isothermal structural relaxation of Glassy, spin-cast Polymer thin films has been investigated. Specifically, the thickness h of freshly cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, It was found to be greater than the equilibrium thickness h(infinity), which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h. (referred to as delta(0)) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h(infinity), and delta(0) is small, whereas in thick films (>500 nm), a plateau value of delta(0) of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of) on thickness is observed regardless of the substrate, Polymer molecular weight, or angular velocity during spin casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the Polymer during the deposition process.