ISSN:0032-3888    

DOI:10.1002/pen.760200102

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAfter defining Fickian diffusion in rubbery polymers an overview of transport behavior in polymers is presented. Diffusion and sorption below the glass transition are discussed, followed by a review and classification of the various theoretical models which have been proposed to account for these phenomena. A short list of recommendations for future work is included.

ISSN:0032-3888    

DOI:10.1002/pen.760200103

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAt temperatures at least 30°C above the glass transition (Tg) the sorption and transport of carbon dioxide in poly(ethylene terephthalate) (PET) can be described conveniently using Henry's law and Fick's law with a constant diffusion coefficient. BelowTgFick's law with a concentration‐ dependent diffusion coefficient, coupled with a sorption isotherm which is concave toward the pressure axis adequately describes the observed sorption and transport data. Physical interpretations of the quantitative deviations from Henry's law and the form of the concentration dependence of the diffusion coefficient is provided by a model which hypothesizes dual modes of sorption and separate non zero mobilities of two populations of sorbed species in local equilibrium. The implications of the observed temperature variations of the phenomenological model parameters are discussed. Dilatometric parameters for PET, polycarbonate, and poly(acrylonitrile) (PAN) are shown to correlate well with a simple. relationship developed to explain the existence of the “extra” mode of sorption responsible for deviations from Henry's law for CO in glassy polymers. In the temperature range fromTgto + 20°C, deviations from Fickian behavior are also apparent. These effects are consistent with a transition in the nature of the polymer from an elastic solid belowTgto a viscous liquid aboveTgIn the narrow temperature range slightly above T the time scale for chain rearrangements apparently approaches that for the diffusion process. The polymer's viscoelastic response to the probing molecule, therefore, causes deviations from the classical time lag predictions. These deviations disappear 30°C

ISSN:0032-3888    

DOI:10.1002/pen.760200104

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractSorption isotherms in the region of low relative pressures have been determined at several temperatures for methane, propane, and chlorodifluoromethane in polystyrene and for propane in bisphenol‐A polycarbonate and poly(vinylacetate). The results are well represented by the isotherm equation of Dual Sorption Theory as applied to glassy polymers. The temperature dependence of the isotherm parameters is examined and discussed; the Langmuir component to sorption decreases as the glass transition temperature is approached and measurements with poly(vinylacetate) confirm that this component is absent above the transition. Average diffusion coefficients were obtained from sorption (desorption) rate curves at constant pressure for propane in polystyrene and polycarbonate and a procedure developed for their analysis to yield the diffusion coefficients of the two sorbed species of penetrant. For the polycarbonate there is evidence of mobility in that fraction of the penetrant: population exhibiting Langmuir‐type sorpt

ISSN:0032-3888    

DOI:10.1002/pen.760200105

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe pressure dependence of the apparent diffusion and permeation coefficients were observed by using the permeation time‐lag method for CO2in glassy poly(ethylene terephthalate) (PET), polystyrene (PS) and poly(vinyl chloride) (PVC) below 1 atm. The results show that the permeation coefficient is constant whereas the diffusion coefficient increases with pressure. According to the theoretical prediction of Paul, it can be concluded that the adsorbed CO2in these glassy polymers is completely immobilized and does not participate directly in the diffusion. A computer was used in the numerical calculation to determine the true diffusion coefficient from the model of Paul,et al. A comparison of the curves calculated with these constants and experimental values gave excellent agreement for the three glassy polymers. But there is a large difference between the values of one of the parameters obtained by this time‐lag method and the sorption method. Relations between this difference and the magnitude of the parameters are discus

ISSN:0032-3888    

DOI:10.1002/pen.760200106

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe dual sorption theory has been extended to the transport of drug molecules through human skinin vitro. By assuming that sorption of drug molecules occurs by both dissolution and binding of drug to immobile sites in the skin, the experimental sorption isotherm can be predicted, and the disparity between steady state and time lag diffusivities can be reconciled. Furthermore, the dual sorption model has been used to develop techniques for controlling these sorption transport processes in order to rapidly achieve predictable transdermal drug deliveryin vivo.

ISSN:0032-3888    

DOI:10.1002/pen.760200107

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractDiffusivitiesDranging over six orders of magnitude with values as low as 2 × 10−13cm2/s have been obtained by a recently developed permeation apparatus, employing a gas‐flow method and a flame ionization detector; LogDfor hydrocarbons in bisphenol‐A polycarbonate (PC) at 120°C is proportional to the square of the molecular diameter (d2) as given by the Lennard‐Jones 6–12 potential. This correlation holds even for the nonspherical n‐hexane molecule. The activation energy for diffusion is also linearly related tod2, with values of 9.5 and 23 kcal/mol for methane and neopentane in PC, respectively. Comparison of PC with two similar polymers of higher glass‐transition temperatures (Tg) indicates that our diffusion data do not correlate with theTgof these polymers. The presence of subsidiary transitions, however, appears to enhance segmental mobilities, increasing the rate of diffusion of the hydrocarbons. The thermodynamic solubility of alkanes in glassy PC can be directly related to their boiling points, and in addition, their enthalpy of solution is linearly related to the heat of condensation of

ISSN:0032-3888    

DOI:10.1002/pen.760200108

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAmorphous polymers are assumed to possess a quasicrystalline structure with chain bundles that are locally parallel over distances ∼1 nm. Two possible types of random motion for a spherical penetrant in such a substrate are described, one type determining the jump frequency and activation energy of diffusion, the other type determining the jump length. The former quantities may be calculated from the model, but not the latter. Sorption of simple gases at low penetrant pressures is assumed to occur mostly in pre‐existing holes, both above and belowTg, and the same penetrant diffusion mechanism is assumed to hold in the two regions. The changes in apparent heat of solution and activation energy of diffusion observed atTgare explained in terms of additional hole formation with increase in temperature aboveTg. The theory is shown to be consistent with experimental diffusion data for several glassy and rubbery systems. Evidence is given that hole formation in simple polymers such as polyethylene may occur by chain “kinking”. For polymers possessing articulated side groups, however, it appears that hole formation arises principally from motions within these

ISSN:0032-3888    

DOI:10.1002/pen.760200109

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractWe have used gas chromatography to study solvent interactions with polysulfone at temperatures below the glass transition. A previously published procedure has been employed to decompose the Gibbs energy of sorption of various solvents in polysulfone into its component contributions from dispersion forces, polar forces, and forces of specific interactions such as hydrogen bonding. The gas chromatographic results and the analysis of Gibbs energy of sorption has been used to establish general criteria for solubility of nonpolar, polar, and specifically interacting solvents in polysulfone.

ISSN:0032-3888    

DOI:10.1002/pen.760200110

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA prediction technique for gas permeability from polymer structure has been developed on the basis of a specific free volume diffusion theory. In this theory, the free volume available per unit mass in a polymer structure controls the rate of gas diffusion and, hence, its rate of permeation. The smaller this specific free volume is, the more difficult the gas diffusion and, thus, the better its barrier to gases becomes. Specifically, the theory predicts a linear relationship between log (permeability) and (−1/specific volume). A number of existing polymers covering six orders of magnitude in CO2permeability and O2permeability were found to follow this correlation. The specific free volume in a polymer was obtained from group contribution calculations. As a result, the gas permeabilities become predictable from the specific volume in a polymer which, in turn, varies with its molecular structure. The advent of this specific free volume theory for gas permeation simplifies greatly the selection of barrier materials for packaging applications. For a given barrier application, a critical specific free volume is first defined from its gas barrier requirement. The polymer structures having specific free volumes smaller than the critical value are then identified. These are the polymers that would have the necessary barrier performance. By this theory, molecular structures, with string polar‐to‐polar interactions and hydrogen‐bonding forces are found to be good barriers to CO

ISSN:0032-3888    

DOI:10.1002/pen.760200111

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY