Influence of crystallinity on gas transprt in polymeric films (original) (raw)
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Gas diffusion in partially crystalline polymers part I: Concentration dependence
Journal of Polymer Science Part B: Polymer Physics, 1996
In this work, a phenomenological model for the gas diffusion in partially crystalline polymers using differential effective medium theory is presented. By making an analogy with the power law known as Archie's law which relates the d.c. conductivity of a brine saturated porous rock to its porosity; we show that gas diffusion through semicrystalline polymers can be described in a similar way. It is assumed that the diffusion coefficient in the crystalline region is zero, while in the amorphous region it is given by a free volume model, and an effective diffusion coefficient Deff, is obtained using the mentioned analogy. The variation of Deff upon concentration is analyzed through its free volume dependence. The crystallinity dependence is considered through an average chain immobilization factor (p), which is explicitely derived. Finally, the results of this model are compared with experimental data given by Kreituss and Frisch, obtaining a good agreement. 0 1996 John Wiley & Sons, Inc. Keywords: diffusion through polymeric films Archie's law effective medium theory concentration dependence Geophysics, 4 3 , 1 2 5 0 (1978).
On the diffusion of gases in partially crystalline polymers
Journal of Polymer Science Part B: Polymer Physics, 1989
The diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient DeB is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita-like free-volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
Macromolecular Symposia, 2010
Summary: Diffusion of n‐hexane in poly(ethylene‐co‐1‐hexene)s with 15–75 wt.% crystallinity was studied by desorption experiments analyzing data using the Fickian equations with a concentration dependent diffusivity. The effect of the impenetrable crystalline phase on the penetrant diffusivity (D) is described by D = Da/(τβ), where Da is the diffusivity of the amorphous polymer, τ is the geometrical impedance factor and β is a factor describing the constraining effect of the crystals on the non‐crystalline phase. For a polymer with 75 wt.% crystallinity, τβ varied markedly with penetrant concentration (v1a) in the penetrable phase: 1000 (v1a = 0) and 10 (v1a = 0.15). This penetrant‐uptake had no effect on the gross crystal morphology, i.e. β must be strongly dependent on v1a. Samples saturated in n‐hexane exhibited a penetrant‐induced loosening of the interfacial structure, as revealed by an increase in crystal density that require an increased mobility in the interfacial component ...
Diffusion in glassy polymers: A model using a homogenization method and the effective medium theory
Journal of Polymer Science Part B: Polymer Physics, 1992
Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows Henry's law and others where it follows Langmuir's law. It is assumed that the linear dimensions of these regions are small compared with the macroscopic length of interest but large compared with the mean free path of the penetrant gas molecules. Applying an homogenization method it is shown that the average flux is directly proportional to the concentration gradient in the polymer. This relationship can be expressed in terms of an effective diffusion coefficient Deff, which depends on the details of the microstructure. D,ff is evaluated in the framework of the effective medium theory and compared with experimental data for diffusion of five vapors in ethylcellulose.
Diffusion of small-molecule penetrants in semicrystalline polymers
Progress in Polymer Science, 1996
This paper is a review of the kinetics of diffusion of small-molecule penetrants in semi-crystalline polymers. The variations in diffusion impedance resulting from variations in morphology and segmental mobility in the amorphous component are highlighted. Deviations from Fickian diffusion appearing in many systems are discussed, as well as the effect of morphology, crystal orientation and chain orientation on the diffusivity.
Gas Transport in Glassy Polymers: Prediction of Diffusional Time Lag
Membranes
The transport of gases in glassy polymeric membranes has been analyzed by means of a fundamental approach based on the nonequilibrium thermodynamic model for glassy polymers (NET-GP) that considers the penetrant chemical potential gradient as the actual driving force of the diffusional process. The diffusivity of a penetrant is thus described as the product of a purely kinetic quantity, the penetrant mobility, and a thermodynamic factor, accounting for the chemical potential dependence on its concentration in the polymer. The NET-GP approach, and the nonequilibrium lattice fluid (NELF) model in particular, describes the thermodynamic behavior of penetrant/polymer mixtures in the glassy state, at each pressure or composition. Moreover, the mobility is considered to follow a simple exponential dependence on penetrant concentration, as typically observed experimentally, using only two adjustable parameters, the infinite dilution penetrant mobility L10 and the plasticization factor β, b...
Diffusion in polymeric systems–A review on free volume theory
Progress in Organic Coatings, 2017
This review paper deals the history and development of various theories to predict the diffusion in polymeric systems. The basis and application of various theories with the prediction capabilities are discussed. The most commonly used theory is Vrentas and Duda free volume theory with excellent agreement with experimental data report so far. This theory predicts the data very accurately in rubbery region. However, few modifications have come up in this theory to predict the diffusion above the glass transition with a little success. Relation between Fujita −Kishimoto theory [15] and Vrentas and Duda Theory [11,12] is
Transition-State Theory Model for the Diffusion Coefficients of Small Penetrants in Glassy Polymers
Macromolecules, 1997
Previous molecular dynamics simulations have shown that the diffusion of a penetrant in a glassy polymer involves occasional jumps between cavities through the opening of a "neck", and thus, because this is a rare event, the diffusion coefficient can be estimated using transition-state theory. We treat this process as a unimolecular rearrangement and develop semiempirical means of estimating the activation energy, frequency factor and jump length. The activation energy is obtained by treating the polymer as a continuous solid and calculating the energy required to expand a neck in that continuum. The model for the frequency factor uses the result from simulations that the distribution of frequencies of the modes in the transition is very similar to that distribution for the reactant state. The frequency factor is estimated by considering only the motion of the penetrant. These motions are treated as harmonic oscillators. The jump length is obtained from simple geometric considerations of the polymer chain. The parameters are readily evaluated from bulk properties of the polymer such as the isothermal compressibility. The model reproduces experimental trends semiquantitatively and could be used to interpolate and extrapolate experimental diffusion data.
Diffusion de la matière dans les polymères
2000
Publikationsansicht. 50590157. Diffusion de la matière dans les polymères (2000). ElAfif, Ali. Details der Publikation. Download, http://www.collectionscanada.ca/obj/s4/f2/ dsk1/tape3/PQDD_0012/NQ60935.pdf. Herausgeber, National ...