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Giulio C Sarti - One of the best experts on this subject based on the ideXlab platform.
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A predictive model for the permeability of gas mixtures in glassy polymers
Fluid Phase Equilibria, 2018Co-Authors: Enrico Toni, Matteo Minelli, Giulio C SartiAbstract:Abstract The transport of gaseous mixtures in glassy polymers is analyzed by means of a thermodynamic based model, which is applied to describe the permeability of CO 2 /CH 4 50/50 binary mixtures in various glassy polymeric membranes. The approach relies on the description of the solubility behavior of penetrant/polymer mixtures provided by the nonequilibrium thermodynamics for glassy polymers (NET-GP), and considers the gradient in penetrant chemical potential of each species as the actual driving force of the diffusive mass fluxes. Such an approach is specialized to dilute solutions conditions, as it is typically of interest for the transport of light gas (e.g. CO 2 , N 2 , CH 4 , O 2 ) in glassy polymeric membranes; that allows for the simple and successful prediction of the gas permeability of gas mixtures based on single component transport data, with no additional parameters required. The NET-GP model is used in combination with an equation of state (lattice fluid theory by Sanchez and Lacombe) to obtain the solubility of pure and mixed gases at various pressures and compositions, as well as the thermodynamic factors accounting for the dependence of chemical potentials of the solutes on the concentrations of both Penetrants. An exponential dependence on penetrant concentration is used to describe the mobility coefficient behavior, so that only two adjustable parameters are required for the pure penetrant case (infinite dilution mobility and plasticization factor). A simple but effective linear mixing rule is considered to describe transport in the binary mixture case, which does not introduce any additional adjustable parameter due to the presence of a second penetrating species. The comparison with permeation data of gas mixtures in different polymers shows the good predictive ability of the model.
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On the interpretation of cryogenic sorption isotherms in glassy polymers
Journal of Membrane Science, 2017Co-Authors: Matteo Minelli, Donald R Paul, Giulio C SartiAbstract:Abstract Sorption data of nitrogen, argon and krypton in different glassy polymers at different cryogenic temperatures are analyzed, including hydrogen in PIM-1; conventional and high free volume glassy polymers are included. A consistent interpretation of experimental data is obtained by considering penetrant dissolution in a uniform dense glassy polymer, undergoing volume swelling with all Penetrants but hydrogen. All the data are properly described by using the NELF model which is appropriate for the solubility in glassy polymers. Remarkably, in each polymer the sorption isotherms of different Penetrants are described well by using the same initial polymer density, and the same swelling coefficient value allows satisfactory description of the sorption behavior of one penetrant at different temperatures. For PIM-1, NELF model and molecular dynamics give exactly the same swelling, and desorption after sorption or subsequent sorption-desorption cycles show hysteresis effects clearly associated to irreversible volume changes; in addition, hydrogen sorption in PIM-1 is fully predicted by the NELF model, simply based on nitrogen sorption, as opposed to BET theory. On the bases of the above results the conclusion is drown that BET theory is not applicable to the cryogenic sorption isotherms in glassy polymers.
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Thermodynamic Modeling of Gas Transport in Glassy Polymeric Membranes
Membranes, 2017Co-Authors: Matteo Minelli, Giulio C SartiAbstract:Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various Penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model.
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Elementary prediction of gas permeability in glassy polymers
Journal of Membrane Science, 2016Co-Authors: Matteo Minelli, Giulio C SartiAbstract:Abstract The transport model proposed by Minelli and Sarti for the representation of gas and vapor permeability in glassy polymers has been extensively applied to various systems, and the model results are thoroughly analyzed. The approach is based on fundamental theory for the diffusion of low penetrant species in polymers, in which the diffusivity is considered as the product of the molecular mobility, and a thermodynamic coefficient, accounting for the concentration dependence of the chemical potential. The model relies on the thermodynamic description of the penetrant/polymer systems provided by the NonEquilibrium Thermodynamics for Glassy Polymers (NET-GP) approach. The penetrant mobility is assumed to depend exponentially on penetrant concentration, and the model contains two parameters only: mobility coefficient at infinite dilution and plasticization factor. The model parameters obtained from the analysis of the permeability behaviors of various systems have been examined and general correlations are derived. The mobility coefficient is indeed correlated to the properties of the pure Penetrants (penetrant molecular size) and pure polymer (fractional free volume and characteristic energy). This allows the derivation of a simple and general expression for the prediction of the permeability of any penetrant species in glassy polymers in the range of low penetrant pressures, as well as the selectivity of any gas pair. Remarkably, the model predictions are able to represent quite accurately the experimental data available in the literature. Furthermore, the plasticization factor is correlated to the swelling produced by the penetrant into the glassy polymer matrix, obtaining thus a reliable tool for the estimation of the pressure dependence of gas permeability on upstream pressure.
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nelf model prediction of the infinite dilution gas solubility in glassy polymers
Journal of Membrane Science, 2007Co-Authors: M. De Angelis, Giulio C Sarti, Ferruccio DoghieriAbstract:Abstract It is observed in general that the solubility of gases and vapors in polymers, both in the rubbery and glassy phase, scales with measures of penetrant condensability, such as the Lennard-Jones parameter, the boiling temperature, or the critical temperature. For rubbery polymers, that behavior was found fully consistent with a simple equilibrium thermodynamic derivation, while no effective theoretical interpretation has been offered so far for the case of glassy polymers. On the other hand, a rigorous expression for the solubility coefficient S 0 in the limit of low pressures can be found based on the NELF model for gas solubility in glassy polymers, which also indicates its dependence on the characteristic parameters of the Penetrants, such as cohesive energy density, molar volume and molecular weight. The values of ln( S 0 ) for a series of gaseous Penetrants have been calculated with the NELF model for several common glassy polymers as polycarbonate (PC), polysulfone (PSf), poly(phenylene oxide) (PPO) and poly(methyl methacrylate) (PMMA). In all cases, ln( S 0 ) is linear with the penetrant critical temperature, T C , and the dependence on temperature and on the polymer fractional free volume can easily be evaluated by the model. The analysis points out also the specific roles of the energetic and entropic contributions to the trend observed for the solubility coefficient in glassy polymers.
Anita J Hill - One of the best experts on this subject based on the ideXlab platform.
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sorption and transport in poly 2 2 bis trifluoromethyl 4 5 difluoro 1 3 dioxole co tetrafluoroethylene containing nanoscale fumed silica
Macromolecules, 2003Co-Authors: Timothy C Merkel, Ingo Pinnau, Benny D Freeman, Pavla Meakin, Anita J HillAbstract:The addition of nanoscale, nonporous fumed silica [FS] particles to size-selective poly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene) [AF2400] systematically increases penetrant permeability coefficients, similar to behavior previously observed in vapor-selective polyacetylenes, but contrary to results in traditional filled polymer systems. Permeability coefficients of large Penetrants increase more than those of small molecules in filled AF2400, thereby decreasing the size selectivity of this polymer. AF2400 is readily plasticized by n-butane, whereas AF2400 containing 40 wt % FS exhibits antiplasticization behavior, suggesting that filler addition alters AF2400 to allow n-butane molecules to be accommodated in the polymer without significant swelling and subsequent plasticization of the matrix. Both filled and unfilled AF2400 have essentially the same gas solubility coefficients, so all of the increase in penetrant permeability in filled AF2400 is a result of increased diffus...
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sorption transport and structural evidence for enhanced free volume in poly 4 methyl 2 pentyne fumed silica nanocomposite membranes
Chemistry of Materials, 2003Co-Authors: Timothy C Merkel, Ingo Pinnau, Benny D Freeman, Richard J Spontak, Pavla Meakin, Anita J HillAbstract:In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS). For instance, the permeability of PMP containing 40 wt % FS to methane is 2.3 times higher than that of the unfilled polymer. Gas and vapor uptake in the PMP/FS nanocomposites is essentially unaffected by the presence of up to 40 wt % FS, while penetrant diffusion coefficients increase regularly with increasing filler content. This increase in diffusivity is responsible for elevated permeability in the PMP/FS nanocomposites. The addition of FS to PMP augments the permeability of large Penetrants more than that of small gases, consistent with a reduction in diffusivity selectivity. Consequently, vapor selectivity in the nanocomposites increases with increasing FS concentration. Activation energies of permeation in PMP decrease with...
Quan Yang - One of the best experts on this subject based on the ideXlab platform.
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molecular level insight of the differences in the diffusion and solubility of Penetrants in polypropylene poly propylmethylsiloxane and poly 4 methyl 2 pentyne
Journal of Membrane Science, 2018Co-Authors: Quan Yang, William I WhitingAbstract:Abstract In order to design optimal polymer membranes it is important to have a molecular level understanding of penetrant transport in such membranes. As such, molecular dynamics simulation was employed to study the diffusion and solubility of gas molecules in polypropylene (PP), poly(propylmethylsiloxane) (PPMS) and poly (4-methyl-2-pentyne) (PMP). After the structures of PP, PPMS and PMP were established and relaxed, the average amplitudes of the oscillation of the main and branch chains of PP, PPMS and PMP were evaluated with a proposed analysis method; in addition the cavity size distributions of PP, PPMS and PMP were determined. PPMS has the largest average cavity size and accessible cavity fraction for Penetrants, followed by PMP and PP, which has the smallest. The logarithm plot of mean-squared displacements (MSDs) versus time for the transport of methane in the three polymers revealed three regimes, namely the ballistic, the subdiffusive and the Fickian diffusive regimes. The ballistic regime of PMP is longer than that of PP and shorter than that of PPMS, because the average cavity size and accessible cavity fraction of PMP are larger than that of PP and smaller than that of PPMS and the Penetrants have less space in PP and more space in PPMS to move freely than they do in PMP before they hit any matrix units. Statistical tests showed that the random walk on a fractal (RWF) model was the most appropriate model to explain the subdiffusion phenomena. The subdiffusive regime is induced by the trap of Penetrants in cavities before they get the chances to jump from cavities to cavities nearby. Next the diffusivities of methane and n-butane were estimated from the plot of MSDs versus time for the penetrant transport in the Fickian diffusive regime. The diffusivities of Penetrants are much smaller in PP than they are in PPMS and PMP and these values are larger in PPMS than they are in PMP. With both unbiased and biased Widom insertion methods, the solubility coefficients K of gas molecules in the polymers were calculated, though biased Widom insertion method has significantly faster calculation speed. PPMS has the largest solubilities of methane and n-butane, followed by PMP and PP, which has the smallest. Though the permeabilities of both methane and n-butane in PPMS are larger than the corresponding values in PMP, the selectivity of n-butane over methane in PPMS is lower than that in PMP. The research results may be employed in membrane design.
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molecular dynamics simulation of Penetrants transport in composite poly 4 methyl 2 pentyne and silica nanoparticles
Journal of Physical Chemistry C, 2012Co-Authors: Quan Yang, Luke E K AchenieAbstract:In industrial processes, membranes made of composite polymer material are widely employed to separate gas mixtures. These membranes have better performance than membranes consisting of polymer alone. To understand the mechanism and therefore aid membrane design, it is essential to explore the penetrant transport in the complex composites from the molecular level, but few researchers have done such research to our knowledge. Herein the penetrant transport in the composite poly(4-methyl-2-pentyne) (PMP) and silica nanoparticle was explored with molecular dynamics (MD) simulations method. The complicated structure of the composite PMP and silica nanoparticle was modeled and with the structure the variation of the cavity size distribution was established due to the existence of nanoparticles. The diffusivity of different Penetrants, including H2, O2, Ar, CH4, and n-C4H10, was determined through least-squares fit of the data of mean square displacement at different times in the Fickian diffusive regime. On the...
Matteo Minelli - One of the best experts on this subject based on the ideXlab platform.
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A predictive model for the permeability of gas mixtures in glassy polymers
Fluid Phase Equilibria, 2018Co-Authors: Enrico Toni, Matteo Minelli, Giulio C SartiAbstract:Abstract The transport of gaseous mixtures in glassy polymers is analyzed by means of a thermodynamic based model, which is applied to describe the permeability of CO 2 /CH 4 50/50 binary mixtures in various glassy polymeric membranes. The approach relies on the description of the solubility behavior of penetrant/polymer mixtures provided by the nonequilibrium thermodynamics for glassy polymers (NET-GP), and considers the gradient in penetrant chemical potential of each species as the actual driving force of the diffusive mass fluxes. Such an approach is specialized to dilute solutions conditions, as it is typically of interest for the transport of light gas (e.g. CO 2 , N 2 , CH 4 , O 2 ) in glassy polymeric membranes; that allows for the simple and successful prediction of the gas permeability of gas mixtures based on single component transport data, with no additional parameters required. The NET-GP model is used in combination with an equation of state (lattice fluid theory by Sanchez and Lacombe) to obtain the solubility of pure and mixed gases at various pressures and compositions, as well as the thermodynamic factors accounting for the dependence of chemical potentials of the solutes on the concentrations of both Penetrants. An exponential dependence on penetrant concentration is used to describe the mobility coefficient behavior, so that only two adjustable parameters are required for the pure penetrant case (infinite dilution mobility and plasticization factor). A simple but effective linear mixing rule is considered to describe transport in the binary mixture case, which does not introduce any additional adjustable parameter due to the presence of a second penetrating species. The comparison with permeation data of gas mixtures in different polymers shows the good predictive ability of the model.
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On the interpretation of cryogenic sorption isotherms in glassy polymers
Journal of Membrane Science, 2017Co-Authors: Matteo Minelli, Donald R Paul, Giulio C SartiAbstract:Abstract Sorption data of nitrogen, argon and krypton in different glassy polymers at different cryogenic temperatures are analyzed, including hydrogen in PIM-1; conventional and high free volume glassy polymers are included. A consistent interpretation of experimental data is obtained by considering penetrant dissolution in a uniform dense glassy polymer, undergoing volume swelling with all Penetrants but hydrogen. All the data are properly described by using the NELF model which is appropriate for the solubility in glassy polymers. Remarkably, in each polymer the sorption isotherms of different Penetrants are described well by using the same initial polymer density, and the same swelling coefficient value allows satisfactory description of the sorption behavior of one penetrant at different temperatures. For PIM-1, NELF model and molecular dynamics give exactly the same swelling, and desorption after sorption or subsequent sorption-desorption cycles show hysteresis effects clearly associated to irreversible volume changes; in addition, hydrogen sorption in PIM-1 is fully predicted by the NELF model, simply based on nitrogen sorption, as opposed to BET theory. On the bases of the above results the conclusion is drown that BET theory is not applicable to the cryogenic sorption isotherms in glassy polymers.
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Thermodynamic Modeling of Gas Transport in Glassy Polymeric Membranes
Membranes, 2017Co-Authors: Matteo Minelli, Giulio C SartiAbstract:Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various Penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model.
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Elementary prediction of gas permeability in glassy polymers
Journal of Membrane Science, 2016Co-Authors: Matteo Minelli, Giulio C SartiAbstract:Abstract The transport model proposed by Minelli and Sarti for the representation of gas and vapor permeability in glassy polymers has been extensively applied to various systems, and the model results are thoroughly analyzed. The approach is based on fundamental theory for the diffusion of low penetrant species in polymers, in which the diffusivity is considered as the product of the molecular mobility, and a thermodynamic coefficient, accounting for the concentration dependence of the chemical potential. The model relies on the thermodynamic description of the penetrant/polymer systems provided by the NonEquilibrium Thermodynamics for Glassy Polymers (NET-GP) approach. The penetrant mobility is assumed to depend exponentially on penetrant concentration, and the model contains two parameters only: mobility coefficient at infinite dilution and plasticization factor. The model parameters obtained from the analysis of the permeability behaviors of various systems have been examined and general correlations are derived. The mobility coefficient is indeed correlated to the properties of the pure Penetrants (penetrant molecular size) and pure polymer (fractional free volume and characteristic energy). This allows the derivation of a simple and general expression for the prediction of the permeability of any penetrant species in glassy polymers in the range of low penetrant pressures, as well as the selectivity of any gas pair. Remarkably, the model predictions are able to represent quite accurately the experimental data available in the literature. Furthermore, the plasticization factor is correlated to the swelling produced by the penetrant into the glassy polymer matrix, obtaining thus a reliable tool for the estimation of the pressure dependence of gas permeability on upstream pressure.
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effect of relative humidity and temperature on gas transport in matrimid experimental study and modeling
Journal of Membrane Science, 2014Co-Authors: Luca Ansaloni, Matteo Minelli, Giacinti M Baschetti, Giulio Cesare SartiAbstract:Abstract The influence of water vapor on the gas permeability of a commercial polyimide, Matrimid ® 5218, has been extensively investigated at three different temperatures (25, 35 and 45 °C), and with four different penetrant gases (CH 4 , N 2 , CO 2 and He), varying the relative humidity in the range 0–75%. In all tests performed, the permeability coefficient decreases as the concentration of water vapor in the membrane increases. In particular, the influence of the presence of water on gas permeability is very similar for all Penetrants, as the same permeability decrease is found, at a given relative humidity, despite the different thermodynamic and kinetic characteristics of the probe gases considered. As temperature is raised, the gas permeability is enhanced, as expected. On the other hand, its decrease with respect to the dry polymer values, as relative humidity increases, is not affected by temperature, and it remains substantially unaltered from 25 to 45 °C, suggesting that such phenomenon can be directly related to the amount of water dissolved in the membrane, which is also unaffected by temperature. Based on the experimental evidence, a simple model is proposed to describe the permeation process under humid conditions, in the framework of the free volume theory. In particular, it has been considered that absorbed water molecules influence gas permeability by occupying polymer free volume, reducing its availability to other Penetrants with lower condensability. The model describes accurately the experimental data using only two adjustable parameters for the polymer-water-penetrant system, once the water solubility is estimated from sorption measurements.
Richard J Spontak - One of the best experts on this subject based on the ideXlab platform.
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nanoscale distribution and segregation of midblock selective co Penetrants in aba triblock copolymer lamellae
RSC Advances, 2013Co-Authors: Evan D Piephoff, K O Rasmussen, Richard J SpontakAbstract:In addition to their attractive and tunable macroscopic properties, microphase-ordered block copolymers serve as model systems capable of providing fundamental insight into the thermodynamic factors that govern the arrangement of spatially-confined molecules in soft, nanostructured environments. Of particular interest in this study is the spatial distribution of co-penetrant molecules in the design of dense polymeric materials intended for use as gas-separation membranes or responsive sensors. Here, we employ self-consistent field theory to examine the spatial distributions of two midblock-selective co-Penetrants in ordered triblock copolymers exhibiting the lamellar morphology. Our results establish how differences in block copolymer incompatibility and penetrant selectivity, size and concentration affect the spatial distributions of the penetrant species, and reveal the extent to which macroscopically miscible Penetrants spatially segregate due to nanoscale confinement.
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sorption transport and structural evidence for enhanced free volume in poly 4 methyl 2 pentyne fumed silica nanocomposite membranes
Chemistry of Materials, 2003Co-Authors: Timothy C Merkel, Ingo Pinnau, Benny D Freeman, Richard J Spontak, Pavla Meakin, Anita J HillAbstract:In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS). For instance, the permeability of PMP containing 40 wt % FS to methane is 2.3 times higher than that of the unfilled polymer. Gas and vapor uptake in the PMP/FS nanocomposites is essentially unaffected by the presence of up to 40 wt % FS, while penetrant diffusion coefficients increase regularly with increasing filler content. This increase in diffusivity is responsible for elevated permeability in the PMP/FS nanocomposites. The addition of FS to PMP augments the permeability of large Penetrants more than that of small gases, consistent with a reduction in diffusivity selectivity. Consequently, vapor selectivity in the nanocomposites increases with increasing FS concentration. Activation energies of permeation in PMP decrease with...