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The diffusion coefficient of ethanol and of n-pentane in PTMSP, at 27°C, was measured as a function of concentration up to a penetrant content of about 12% by weight, for polymer samples obtained through different processes; differential sorptions and desorptions with vapor phases were considered. In the case of ethanol a nonmonotonous behavior was observed for the diffusivity, while in the case of n-pentane the same property was found to monotonously decrease with increasing the penetrant content. The sorption isotherms were also reported, indicating that n-pentane exhibits a typical dual mode behavior, while ethanol follows an unusual s-shape curve. The chemical potential of the dissolved penetrants, calculated directly from the isotherms, shows the very different importance of the energetic interactions of the two penetrants with the polymer units. In spite of the remarkably different concentration dependencies observed for both solubility and diffusivity of the two penetrants, the mobility factors are in both cases monotonously decreasing with the penetrant concentration, and follow very similar trends. The significant differences observed for the concentration dependence of the diffusion coefficients are, thus, associated to the thermodynamic contributions, which are very different for n-pentane and ethanol. Different polymeric films, obtained through different solvent evaporation processes, show quite different solubility, diffusivity and mobility for both ethanol and n-pentane. On the other hand, the ratio between the mobility of the two penetrants as well as the slope of mobility as function of the concentration remains the same for all the different samples inspected. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2245–2258, 1997

The representation of liquid–liquid equilibria (LLE) in ternary systems composed by water, 1,4-dioxane and different grades of poly(lactic acid) (PDLLA and PLLA), has been addressed through the PC-SAFT equation of state (EoS), in which the scheme of induced association is used to represent the interaction between solvent (dioxane) and non-solvent (water). The model parameters devoted to the description of pure component properties, as well as those pertinent to the representation of thermodynamic behaviour of solvent/non-solvent mixtures, were tuned on the basis of specific pressure–volume–temperature (PVT) data for the corresponding systems. Only the binary parameters for polymer–solvent and polymer/non-solvent pairs were adjusted to obtain a useful representation of experimental LLE data for the ternary systems. A suitable description of the thermodynamic properties of ternary mixtures was obtained using temperature-independent binary interaction parameters in the range 25–80 °C, and the consistency of the approach in the entire composition range was verified against experimental solubility data specifically measured for the polymer/non-solvent pair. The model shows good ability in the description of the thermodynamic properties of the system and it represents a reliable tool for the prediction of LLE also at conditions different from those considered for its set-up. This approach thus represents a useful designing tool for processes, such as thermally induced phase separation (TIPS), used in the preparation of microporous polymeric scaffolds.

The sorption of organic vapors of different chemical nature, molecular weight and polarity in glassy Matrimid 5218 polyimide films is measured and modeled in the entire activity range up to saturated vapor conditions. Experimental isotherms show several different peculiarities according to the nature of the solute component, consistent with the glassy character of the polymeric matrix. These features range from high vapor solubility coefficient at infinite dilution to swelling and plasticization of the polymer matrix depending on temperature and solute affinity. The various behaviors are then discussed by means of a thermodynamic model for properties of glassy polymeric phases. Indeed, the Non-Equilibrium Lattice Fluid (NELF) model is used to interpret the Vapor-Liquid-Equilibrium below Tg, while the corresponding equilibrium Lattice Fluid model was considered to the same purpose for the case of plasticization conditions in the system. This representation is able to describe consistently all different observed features and allows for a predictive procedure to reproduce solubility isotherms over a wide activity range.

The nonequilibrium lattice fluid (NELF) model is here implemented with a simplified relation for bulk rheological behavior of glassy polymers, to obtain a predictive model for pseudoequilibrium solute content and volume dilation induced by swelling agents. The rheological model discussed in this work is ultimately used to derive a relation for the pseudoequilibrium volume of the polymeric system as a function of temperature and solute fugacity. The model makes use of two nonequilibrium parameters which, in turn, can be determined through the analysis of nonequilibrium pVT properties of the polymeric species. The predictive ability of the new model for solubility and volume swelling was tested by means of the comparison of model predictions and correlations with experimental data, available in the literature, for different polymer/penetrant pairs. The results obtained from the comparison allow one to conclude that the model is not just useful to describe the swelling effect of penetrants but also to recognize conditions at which plasticization by solute species induces a glass to rubber transition in the polymeric system.

The transport properties of high free volume glassy polymers such as poly(1-trimethylsilyl-1-propyne) (PTMSP) were analyzed by comparing the steady state permeation behavior with the transient diffusion of light hydrocarbons. It has been observed that the apparent diffusivity measured in the two different modes are indeed quite different from one another, even by nearly an order of magnitude. The behavior can be explained by considering the high free volume glassy polymer as a two-phase system formed by a continuous solid phase and a discontinuous nano-void phase, with a suitable degree of interconnections. The influence of pore distribution and pore connectivity on the differences observed between transient sorption and steady permeation behavior has been analyzed by performing various mathematical simulations of transient and steady state diffusion for different morphological structures of the two phase system, used to model the polymer matrix. Qualitative comparison indicates that the difference experimentally observed is associated to a pore interconnectivity effect and to the corresponding anisotropy in pore distribution.

A comprehensive study of the gas barrier properties of hybrid organic–inorganic coatings formed by polyvinyl alcohol (PVOH) and Si-SiO2, obtained via sol–gel technique, was carried out. It has been shown that the oxygen, nitrogen and carbon dioxide transfer rates of barrier polymers such as poly(ethylene terephthalate) and oriented polypropylene can be further reduced, by up to two orders of magnitude, with a thin coating (1–2 μm) of PVOH/Si-SiO2. More notably, it has been observed that the material maintains this feature even after a prolonged contact with water, which is a strong solvent for PVOH. Direct moisture sorption measurements show that silica lowers the water uptake of PVOH and inhibits sorption-induced swelling and plasticization of the polymer. Correlations between the gas transport properties of the hybrid coatings and factors such as the silica content, the type of polymeric substrate, the nature of penetrant and the temperature have been found, providing guidelines for the selection and design of multilayer materials for packaging applications. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

The nonequilibrium thermodynamics of glassy polymers (NET-GP) approach (Macromolecules 2005, 38, 10299.) has been applied to the development of a one-dimensional transport model aimed at describing the kinetics of sorption and dilation of polymeric films in supercritical carbon dioxide. The NET-GP model was combined with a simple rheological constitutive equation to build a sorption-diffusion-relaxation model able to describe mass uptake and swelling kinetics of polymeric films in contact with carbon dioxide over a wide range of pressures and temperatures. The model calculations are compared with data on mass sorption kinetics for CO2 in supported glassy poly(methyl methacrylate) (PMMA) films, measured in a high-pressure quartz crystal microbalance (QCM).

A new experimental apparatus has been set up to analyze the polymer dilation as well as the stress profile induced by vapour sorption in constrained films. The device couples the bending cantilever technique with a new digital micrometer which allows to measure both deflection and polymer swelling at the same time. The apparatus has been applied to study the effects of acetonitrile mass uptake in polycarbonate at 40°C, obtaining the time evolution of swelling and of cantilever deflection during integral sorption tests, in the activity range from zero up to 0.35. A simulation model is also proposed, which couples Fick’s law for diffusion to the study of strain and stress distributions in the cantilever; the mechanical problem has been formulated following the classical laminate theory. The relevant values of the material properties entering the model, as solubility, diffusivity and penetrant induced dilation, have all been determined through separate independent measurements, and the results obtained are in good agreement with the corresponding values reported in the literature. The simulation model is able to predict with good precision both the kinetics of deflection during sorption and its final equilibrium value, as well as the overall swelling kinetics, with no need of any adjustable parameters. The model allows also to calculate the time evolution of the stress profile in the polymer film during sorption/desorption steps.

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.

Solubility isotherms for n-pentane and n-hexane were measured in pure poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and in 1-trimethylsilyl-1-propyne/1-trimethylsilyl-1-n-hexyne 70/30 copolymer, using freshly prepared samples as well as aged films, at different temperatures. The experimental values of penetrant diffusivity, mobility and heat of mixing have been reported and discussed, based on direct positron annihilation lifetime spectroscopy information, Dual Mode Sorption Model and Non-Equilibrium Lattice Fluid model. The ageing effect is more pronounced in PTMSP, where it leads to a significant solubility and diffusivity reduction, than in the copolymer where the effect is less important. In the activity range inspected the diffusion coefficient and the heat of mixing are almost concentration independent for PTMSP, while they increase appreciably with concentration in the copolymer, as an effect of the great difference in the free volume present in the two matrices.

The oxygen permeability of composite materials, consisting of a LDPE substrate coated with a thin layer (0.7–1 μm) of new hybrid organic/inorganic materials based on SiO 2 and PE-PEG block copolymers, has been characterized at 35 and 50 °C. The effect of adding a second organic component capable to form hydrogen bonds, namely either poly(4-hydroxystyrene) (PHS) or malic acid, has been studied. While the addition of PHS leads to a further significant decrease (50–70%) of the oxygen permeability both at 35 and 50 °C, on the contrary, the addition of malic acid leads to poorer barrier properties. A slight decrease of the permeability was obtained after plasma treatment of the LDPE surface.

Well established equation-of-state (EoS) models from Perturbed Hard Sphere Chain Theory have been adopted within the framework of non-equilibrium thermodynamics for glassy polymers (NET-GP) to describe the solubility of small penetrants in glassy polymers. The procedure presented here parallels the one already applied to the Lattice Fluid EoS, obtaining the Non-Equilibrium Lattice Fluid (NELF) model. The solubility is calculated as pseudo-equilibrium solute content in the glassy polymeric phase at fixed temperature and solute fugacity, and is compared to the experimental data. The NE-PHSC model predictions require pure component and binary EoS parameters, together with the value of the glassy polymer density during sorption. Several common glassy polymers, as well as a high free volume fluoropolymer, have been considered to test the model ability to represent the thermodynamic properties of glassy gas–polymer mixtures. A comparison between the performance of two NE-PHSC models, endowed with different expressions for the interaction potential, is also presented, offering interesting conclusions on their accuracy in the representation of the thermodynamic properties of relatively high-density systems. The results obtained in this work show that the NET-GP approach provides a reliable description of the properties of homogeneous glassy mixtures.

The solubility of C2H6 and C2F6 in two amorphous glassy fluoropolymers, Teflon® AF1600 and AF2400, has been modeled with the non equilibrium statistical associating fluid (NE-SAFT) and non equilibrium perturbed hard sphere chain (NE-PHSC) theories. Experimental swelling data during sorption are available to obtain a complete prediction of the solubility isotherms at 35°C. The solubility of C2F6 in both fluoropolymers is rather satisfactorily predicted by the models with no adjustable parameters, while that of C2H6 is overestimated, and a correction factor equal to about 0.90 must be applied on the binary energetic interactions estimated with the first approximation mixing rule. This result, combined with what previously obtained with the NE-lattice fluid (NE-LF) model, reveals inadequate representation of the hydrocarbon solubility in fluoropolymers by the geometric mean rule used to estimate the binary energetic interactions.

A new procedure is introduced for the calculation of solubility isotherms of plasticizing agents in glassy polymer matrices with particular application to the case of absorption of supercritical gases in bulk glassy polymer films. The model presented is an extension of the nonequilibrium thermodynamics for glassy polymers (NET-GP) approach, modified to allow for the calculation of the effects of pressure, temperature, and gas concentration on the glass transition. Mass sorption and one- dimensional swelling behavior are analyzed for the carbon dioxide (CO2)-poly(methyl methacrylate) (PMMA) system at high pressure. A quantitative comparison is presented between the model performance and experimental data measured using quartz crystal microbalance (QCM) and high-pressure ellipsometry (HPE).

Sorption experiments of DCM in Matrimid were performed with gravimetric method by means of a Quartz Crystal Microbalance (QCM) and of a Quartz Spring (QS) balance, that have been described elsewhere. Experiments were run at different temperatures, ranging from 10°C to 40°C, in differential activity steps at each temperature. Matrimid 5218 was spin coated on the quartz resonators of QCM from a 1% solution in dichloromethane and then treated for 24 hours at 50°C in a vacuum oven.

In the present work, the solubility of a series of liquid penetrants (water, n-alkanes, alkyl-alcohols, ethyl acetate, acetone, edible oil components) has been inspected at room temperature, into dense films of both glassy (Matrimid 5218) and rubbery (crosslinked PDMS) polymers.