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Anita J Hill - One of the best experts on this subject based on the ideXlab platform.
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membranes with artificial Free Volume for biofuel production
Nature Communications, 2015Co-Authors: Nikos Petzetakis, Cara M. Doherty, Anita J Hill, Aaron W Thornton, Chelsea X Chen, Pepa Cotanda, Nitash P BalsaraAbstract:Free-Volume of polymers governs transport of penetrants through polymeric films. Control over Free-Volume is thus important for the development of better membranes for a wide variety of applications such as gas separations, pharmaceutical purifications and energy storage. To date, methodologies used to create materials with different amounts of Free-Volume are based primarily on chemical synthesis of new polymers. Here we report a simple methodology for generating Free-Volume based on the self-assembly of polyethylene-b-polydimethylsiloxane-b-polyethylene triblock copolymers. We have used this method to fabricate a series of membranes with identical compositions but with different amounts of Free-Volume. We use the term artificial Free-Volume to refer to the additional Free-Volume created by self-assembly. The effect of artificial Free-Volume on selective transport through the membranes was tested using butanol/water and ethanol/water mixtures due to their importance in biofuel production. We found that the introduction of artificial Free-Volume improves both alcohol permeability and selectivity.
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Free Volume characterization of sulfonated styrenic pentablock copolymers using positron annihilation lifetime spectroscopy
Journal of Membrane Science, 2014Co-Authors: Geoffrey M Geise, Anita J Hill, Cara M. Doherty, Benny D Freeman, Donald R PaulAbstract:Abstract A series of sulfonated styrenic pentablock copolymers was characterized using positron annihilation lifetime spectroscopy (PALS). Ortho -positronium ( o -Ps) lifetime was measured as a function of the polymer's degree of sulfonation and the environment in which the polymer was equilibrated. Samples ranged from an un-sulfonated styrenic pentablock copolymer to one with an ion exchange capacity (IEC) of 2.0 meq/g(dry polymer), and the samples were equilibrated in either air having 50% relative humidity, de-ionized (DI) water, or 2000 mg L −1 aqueous NaCl solution environments. The o -Ps lifetime, and thus, the average Free Volume element size, decreased as the polymer's degree of sulfonation increased and as the amount of water sorbed into the polymer increased, similar to reported decreases in o -Ps lifetime accompanying increased water sorption in uncharged cross-linked poly(ethylene glycol) hydrogels. The o -Ps lifetimes of the DI water equilibrated acid counter-ion form polymers were quite similar to those of the salt solution equilibrated sodium counter-ion form polymers, suggesting that the PALS data are not particularly sensitive to the counter-ion form of these hydrated polymers. Previously reported water and salt permeability data in polymers were correlated with the PALS data. Correlating water and salt permeability with Free Volume data, estimated using o -Ps lifetime, was complicated by the micro-phase separated nature of the block copolymers. The water permeability of polymers whose hydrophilic micro-domains are believed to be well connected correlated with Free Volume data, based on o -Ps lifetime. Salt permeability, however, did not correlate with Free Volume data estimated from o -Ps lifetime, according to Free Volume theory. In general, contributions of the hydrophobic micro-domain Free Volume to the PALS measurement frustrate the correlation of water and salt transport properties with PALS parameters in a manner that is not observed in other sulfonated and uncharged polymers.
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effect of Free Volume on water and salt transport properties in directly copolymerized disulfonated poly arylene ether sulfone random copolymers
Macromolecules, 2011Co-Authors: Wei Xie, Anita J Hill, Benny D Freeman, Geoffrey M Geise, James I Mardel, James E McgrathAbstract:The influence of cation form and degree of sulfonation on Free Volume, as probed via positron annihilation lifetime spectroscopy (PALS), and water and salt transport properties was determined in a systematic series of directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers. Polymer samples were studied in both the dry and hydrated states. PALS-based estimates of Free Volume in the dry polymers were compared with those estimated using density and the Bondi group contribution method, and PALS-based Free Volume data for hydrated polymers were correlated with water and salt transport properties. The transport properties depend strongly on Free Volume cavity size. Samples with larger Free Volume elements have higher water and salt solubility, diffusivity, and permeability and lower water/salt diffusivity and permeability selectivity. Sorption of water alters the characteristic Free Volume of the polymer matrix by two competing mechanisms: water molecules partially occupy the original ...
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gas separation Free Volume distribution and physical aging of a highly microporous spirobisindane polymer
Chemistry of Materials, 2008Co-Authors: Chad L Staiger, Anita J Hill, Steven J Pas, Chris J CorneliusAbstract:PALS results show a bimodal pore size distribution for a spirobisindane polymer, with the majority of pores being of the larger size. Gas permeability, density and PALS results suggest the polymer undergoes physical aging during permeability testing. PALS results also show that solution processing generates extra Free Volume above the intrinsic Free Volume of the precipitated polymer.
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impact of average Free Volume element size on transport in stereoisomers of polynorbornene i properties at 35 c
Journal of Polymer Science Part B, 2003Co-Authors: Broderick R Wilks, Anita J Hill, Won J Chung, Peter J Ludovice, Mary R Rezac, Pavla MeakinAbstract:This article demonstrates that transport of gases through glassy polymers is significantly influenced not only by the absolute amount but also by the distribution of Free Volume. Two stereoisomers of polynorbornene with nearly equivalent total Free Volume, but markedly different average Free-Volume sizes, were evaluated. The Free-Volume element size was probed with positron annihilation lifetime spectroscopy, wide-angle X-ray scattering, gas sorption, and molecular modeling. The permeation, sorption, and diffusion of light gases were measured in each stereoisomer at 35 °C. All analytical techniques indicated that one isomer (labeled as Architecture II) had a larger average Free-Volume element size but fewer elements. This isomer also had a very slightly higher bulk density (1.000 vs 0.992 g/cm3 for the other stereoisomer). Architecture II also had gas sorption and diffusion coefficients that were two to three times those of the less dense counterpart. These differences have been attributed to differences in the Free-Volume element size available within the polymer matrix. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2185–2199, 2003
V P Shantarovich - One of the best experts on this subject based on the ideXlab platform.
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Free Volume distributions in ultrahigh and lower Free Volume polymers comparison between molecular modeling and positron lifetime studies
Macromolecules, 2002Co-Authors: Dieter Hofmann, Matthias Heuchel, Yuri Yampolskii, V S Khotimskii, V P ShantarovichAbstract:The present paper deals with important differences in the distribution of Free Volume in high and low Free Volume polymers as indicated by a joint investigation utilizing molecular modeling and positron annihilation lifetime studies. The main focus of this paper is on the molecular modeling approach. The polymers in question are the ultrahigh Free Volume polymer poly(1-(trimethylsilyl)-1-propyne) (PTMSP) and two polystyrene derivatives containing Si and F. Extended equilibration procedures were necessary to obtain reasonable packing models for the polymers. The transition state Gusev−Suter Monte Carlo method was utilized to prove a reasonable agreement between simulated and measured diffusivity and solubility values for the model structures. The Free Volume distribution was analyzed for the validated packing models and compared with respective positron annihilation data. In both cases, a bimodal distribution of Free Volume was observed for PTMSP while the polystyrene derivatives as other conventional glas...
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gas permeability and Free Volume of highly branched substituted acetylene polymers
Macromolecules, 2001Co-Authors: Yuri Yampolskii, V P Shantarovich, Benny D Freeman, A P Korikov, Kazukiyo Nagai, Toshio Masuda, Masahiro Teraguchi, Giseop KwakAbstract:Gas permeation, sorption, and structural properties of two highly branched polyacetylenes, poly[1-phenyl-2-[p-(triphenylsilyl)phenyl]acetylene] (PPhSiDPA) and poly[1-phenyl-2-[p-(triisopropylsilyl)phenyl]acetylene] (PPrSiDPA), are reported. Structurally, both polymers have much in common; however, their transport properties are quite different. PPhSiDPA has dramatically lower permeability coefficients than PPrSiDPA. For example, the O2 permeability coefficients of PPhSiDPA and PPrSiDPA are 12 × 10-10 and 230 × 10-10 cm3 (STP) cm/(cm2 s cmHg), respectively, at 22 °C. Gas solubility is very high in PPrSiDPA, similar to that observed in poly(1-trimethysilyl-1-propyne) (PTMSP), the most permeable polymer known. Gas solubility coefficients of PPhSiDPA are 2−3 times lower than those of PPrSiDPA. Free Volume size and size distribution were characterized using positron annihilation lifetime (PAL) spectroscopy. Results from these studies (i.e., a bimodal size distribution of Free Volume elements and large Free vol...
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positron annihilation lifetime study of high and low Free Volume glassy polymers effects of Free Volume sizes on the permeability and permselectivity
Macromolecules, 2000Co-Authors: V P Shantarovich, Yu. P. Yampolskii, I B Kevdina, Yu A AlentievAbstract:Free Volume in a big group of glassy polymers distinguished by a wide range of gas permeability (P in the range 1−104 Barrer) was studied using the positron annihilation lifetime (PAL) method. To take into account an additional channel of decay of positronium (Ps), caused by the reaction with sorbed O2, measurements were performed both under ambient conditions and under a nitrogen atmosphere. The finite-term and continuous lifetime analyses (PATFIT and CONTIN programs) were used for the treatment of the positron annihilation decay curves. It was shown that better statistical fitting parameters can be obtained for four component PAL spectra of a vast majority of the glassy polymers studied. The presence of two Ps lifetimes (τ3 = 1.7−3.3 ns and τ4 = 2.7−10.9 ns) indicates that size distribution of Free Volume elements (FVE) in glassy polymers is typically bimodal. The presence of smaller and larger FVE (R3 = 2.5−3.5 A, R4 = 3.5−7.0 A) was proved by PATFIT analysis of the data. Continuous analysis clearly in...
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high transport parameters and Free Volume of perfluorodioxole copolymers
Journal of Membrane Science, 1997Co-Authors: Yu A Alentiev, Yu. P. Yampolskii, V P Shantarovich, S Nemser, N A PlateAbstract:Abstract Permeability (P) and diffusion (D) coefficients of perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene copolymers were determined with respect to different gases (He, H2, O2, N2, CO2, hydrocarbons C1C3). The copolymers with large content of perfluorodioxole comonomer exhibit high permeability with respect to lighter gases comparable to that of poly(trimethylsilyl propyne). However, the copolymers studied are much more permselective than the latter polymer. Free Volume as estimated via Bondi's method and Free Volume size distribution parameters which were determined by means of positron annihilation lifetimes (PAL) method are also unusually high if compared with other glassy polymers. A novel correlation of the P and D values, as well as of the solubility coefficients S with the PAL parameter t 4 I 4 are reported.
Benny D Freeman - One of the best experts on this subject based on the ideXlab platform.
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modeling water diffusion in polybenzimidazole membranes using partial immobilization and Free Volume theory
Polymer, 2020Co-Authors: Joshua D Moon, Benny D Freeman, Michele Galizia, Hailun Borjigin, Ran Liu, Judy S Riffle, Donald R PaulAbstract:Abstract This study extends previous work on modeling water sorption, dilation, and diffusion in polybenzimidazoles (PBIs) by comparing water transport properties of commercial PBI (Celazole®) with three sulfone-containing PBIs. A model is developed combining Free Volume and partial immobilization theories to describe water diffusion coefficients across a wide range of concentrations and degrees of swelling. Water vapor sorption and dilation follow dual-mode behavior and generally correlate with the availability of strong hydrogen bonding sites on the polymer chains. At low concentrations, water diffusion coefficients are suppressed by partial immobilization of Langmuir species, while at high concentrations, water diffusion coefficients increase due to significant swelling and plasticization. To account for the influence of plasticization on Free Volume and water mobility, local Henry's law mobility coefficients are correlated with fractional Free Volume (FFV), where the Volume occupied by water molecules is considered to contribute to dynamic Free Volume and is assumed to be as accessible for water diffusion as unoccupied Free Volume. Contributions to diffusion coefficients from thermodynamic and convective frame of reference effects and concentration averaging are also considered.
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Free Volume characterization of sulfonated styrenic pentablock copolymers using positron annihilation lifetime spectroscopy
Journal of Membrane Science, 2014Co-Authors: Geoffrey M Geise, Anita J Hill, Cara M. Doherty, Benny D Freeman, Donald R PaulAbstract:Abstract A series of sulfonated styrenic pentablock copolymers was characterized using positron annihilation lifetime spectroscopy (PALS). Ortho -positronium ( o -Ps) lifetime was measured as a function of the polymer's degree of sulfonation and the environment in which the polymer was equilibrated. Samples ranged from an un-sulfonated styrenic pentablock copolymer to one with an ion exchange capacity (IEC) of 2.0 meq/g(dry polymer), and the samples were equilibrated in either air having 50% relative humidity, de-ionized (DI) water, or 2000 mg L −1 aqueous NaCl solution environments. The o -Ps lifetime, and thus, the average Free Volume element size, decreased as the polymer's degree of sulfonation increased and as the amount of water sorbed into the polymer increased, similar to reported decreases in o -Ps lifetime accompanying increased water sorption in uncharged cross-linked poly(ethylene glycol) hydrogels. The o -Ps lifetimes of the DI water equilibrated acid counter-ion form polymers were quite similar to those of the salt solution equilibrated sodium counter-ion form polymers, suggesting that the PALS data are not particularly sensitive to the counter-ion form of these hydrated polymers. Previously reported water and salt permeability data in polymers were correlated with the PALS data. Correlating water and salt permeability with Free Volume data, estimated using o -Ps lifetime, was complicated by the micro-phase separated nature of the block copolymers. The water permeability of polymers whose hydrophilic micro-domains are believed to be well connected correlated with Free Volume data, based on o -Ps lifetime. Salt permeability, however, did not correlate with Free Volume data estimated from o -Ps lifetime, according to Free Volume theory. In general, contributions of the hydrophobic micro-domain Free Volume to the PALS measurement frustrate the correlation of water and salt transport properties with PALS parameters in a manner that is not observed in other sulfonated and uncharged polymers.
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effect of Free Volume on water and salt transport properties in directly copolymerized disulfonated poly arylene ether sulfone random copolymers
Macromolecules, 2011Co-Authors: Wei Xie, Anita J Hill, Benny D Freeman, Geoffrey M Geise, James I Mardel, James E McgrathAbstract:The influence of cation form and degree of sulfonation on Free Volume, as probed via positron annihilation lifetime spectroscopy (PALS), and water and salt transport properties was determined in a systematic series of directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers. Polymer samples were studied in both the dry and hydrated states. PALS-based estimates of Free Volume in the dry polymers were compared with those estimated using density and the Bondi group contribution method, and PALS-based Free Volume data for hydrated polymers were correlated with water and salt transport properties. The transport properties depend strongly on Free Volume cavity size. Samples with larger Free Volume elements have higher water and salt solubility, diffusivity, and permeability and lower water/salt diffusivity and permeability selectivity. Sorption of water alters the characteristic Free Volume of the polymer matrix by two competing mechanisms: water molecules partially occupy the original ...
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cavity size distributions in high Free Volume glassy polymers by molecular simulation
Polymer, 2004Co-Authors: Xiaoyan Wang, Kenneth M Lee, Matthew T Stone, Isaac C Sanchez, Benny D FreemanAbstract:Abstract Two very permeable polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP) and a random copolymer of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (TFE/BDD), have very similar and large fractional Free Volumes (FFV), but very different permeabilities. Using atomistic models, cavity size (Free Volume) distributions determined by a combination of molecular dynamic and Monte Carlo methods are consistent with the observation that PTMSP is more permeable than TFE/BDD. The average spherical cavity size in PTMSP is 11.2 A whereas it is only 8.2 A in TFE/BDD. These cavity size distributions determined by simulation are also consistent with Free Volume distributions determined by positron annihilation lifetime spectroscopy.
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gas permeability and Free Volume of highly branched substituted acetylene polymers
Macromolecules, 2001Co-Authors: Yuri Yampolskii, V P Shantarovich, Benny D Freeman, A P Korikov, Kazukiyo Nagai, Toshio Masuda, Masahiro Teraguchi, Giseop KwakAbstract:Gas permeation, sorption, and structural properties of two highly branched polyacetylenes, poly[1-phenyl-2-[p-(triphenylsilyl)phenyl]acetylene] (PPhSiDPA) and poly[1-phenyl-2-[p-(triisopropylsilyl)phenyl]acetylene] (PPrSiDPA), are reported. Structurally, both polymers have much in common; however, their transport properties are quite different. PPhSiDPA has dramatically lower permeability coefficients than PPrSiDPA. For example, the O2 permeability coefficients of PPhSiDPA and PPrSiDPA are 12 × 10-10 and 230 × 10-10 cm3 (STP) cm/(cm2 s cmHg), respectively, at 22 °C. Gas solubility is very high in PPrSiDPA, similar to that observed in poly(1-trimethysilyl-1-propyne) (PTMSP), the most permeable polymer known. Gas solubility coefficients of PPhSiDPA are 2−3 times lower than those of PPrSiDPA. Free Volume size and size distribution were characterized using positron annihilation lifetime (PAL) spectroscopy. Results from these studies (i.e., a bimodal size distribution of Free Volume elements and large Free vol...
David L Mcdowell - One of the best experts on this subject based on the ideXlab platform.
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evolution of structure and Free Volume in symmetric tilt grain boundaries during dislocation nucleation
Acta Materialia, 2010Co-Authors: Garritt J Tucker, M A Tschopp, David L McdowellAbstract:Abstract Grain boundary evolution in copper bicrystals is investigated during uniaxial tension at 10 K. Grain boundary structures are generated using molecular statics employing an embedded atom method potential, followed by molecular dynamics simulation at a constant 1 × 109 s−1 strain rate. Interfacial Free Volume is continuously measured during boundary deformation, and its evolution is investigated both prior to and during grain boundary dislocation nucleation. Free Volume provides valuable insight into atomic-scale processes associated with stress-induced grain boundary deformation. Different boundary structures are investigated in this work to analyze the role of interface structure, stress state and initial Free Volume on dislocation nucleation. The results indicate that the Free Volume influences interfacial deformation through modified atomic-scale processes, and grain boundaries containing particular Free Volume distributions show a greater propensity for collective atomic migration during inelastic deformation.
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structure and Free Volume of 1 1 0 symmetric tilt grain boundaries with the e structural unit
Acta Materialia, 2007Co-Authors: M A Tschopp, Garritt J Tucker, David L McdowellAbstract:Abstract Atomistic simulations are used to investigate the structure and interfacial Free Volume of 〈1 1 0〉 symmetric tilt grain boundaries in copper containing the E structural unit from the Σ 9(2 2 1) θ = 141.1° grain boundary. In this work, a stereologically-based methodology is used to calculate the grain boundary Free Volume along with the spacing and connectivity of Free Volume. After generating the minimum energy equilibrium grain boundary, we examine (i) the grain boundary structure, (ii) a measure of Free Volume associated with the grain boundary, (iii) spatial correlation functions of the distribution of Free Volume, and (iv) images of grain boundary Free Volume distribution. Using the results from these calculations, the influence of Free Volume spatial distribution and grain boundary structure on dislocation dissociation and nucleation is briefly discussed for boundaries with the E structural unit subjected to tensile loading normal to the interface along with the potential implications of Free Volume connectivity.
Yong Yang - One of the best experts on this subject based on the ideXlab platform.
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atomistic Free Volume zones and inelastic deformation of metallic glasses
Nature Materials, 2010Co-Authors: C T Liu, Qing Wang, Yong YangAbstract:The amorphous nature of metallic glasses and their mechanical properties make them interesting for structural applications. However, the interplay between the nature of atomic structures in metallic glasses and mechanical properties remains poorly understood. In this study, high-frequency dynamic micropillar tests have been used to probe both atomic clusters and flow defects in metallic glasses. We show that loosely bonded atomistic Free-Volume zones that are enveloped elastically by tightly bonded atomic clusters show a deformation character similar to supercooled liquids. At room temperature, the effective viscosity of these Free-Volume zones is of the order of 1 x 10(8) Pa s before the occurrence of shear banding. The confined liquid-like deformation of Free-Volume zones leads to significant mechanical hysteresis in micropillars under dynamic loading, providing important insight into how atomistic structural features affect the deformation behaviours in metallic glasses in the apparent elastic regime. The inelastic behaviour also serves as the basis for the superior damping resistance of metallic glasses.
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atomistic Free Volume zones and inelastic deformation of metallic glasses
Nature Materials, 2010Co-Authors: C T Liu, Qiang Wang, Yong YangAbstract:The amorphous nature of metallic glasses makes them interesting for structural applications. However, the interplay between the nature of atomic structures and mechanical properties remains poorly understood. Dynamic micropillar tests now show the important contribution of the inelastic deformation of atomistic Free-Volume zones to the deformation behaviour of metallic glasses.
