Glassy polymers penetrant-induced effects

The swelling mechanism is well established in rubbers (Flory, 1943). The expansion force generated by the solvent penetration is equilibrated by the entropic force linked to chain stretching. Little is known, in contrast, for the case of glassy polymers where plasticization effects are not sufficient to induce a devitrification. Swelling can be defined by... 

Penetrant-Induced Effects. History-dependent properties of glassy polymers are well documented in terms of thermal (113,114) and mechanical U15) properties. Studies have related excess enthalpy changes measured by differential scanning calorimetry to changes in small-molecule sorption (116,117). Many studies have reported penetrant-induced history-dependent (or conditioning) effects for gas and vapor sorption and transport properties in glassy... 

Chapter 4(71) focuses on the characterization of sorption kinetics in several glassy polymers for a broad spectrum of penetrants ranging from the fixed gases to organic vapors. The sorption kinetics and equilibria of these diverse penetrants are rationalized in terms of the polymer-penetrant interaction parameter and the effective glass transition of the polymer relative to the temperature of measurement. The kinetic response is shown to transition systematically from concentration independent diffusion, to concentration dependent diffusion, and finally to complex nonFickian responses. The nonFickian behavior involves so-called "Case II" and other anomalous situations in which a coupling exists between the diffusion process and mechanical property relaxations in the polymer that are induced by the invasion of the penetrant (72-78). ... 

Oriontation-Induced Effects. Orientation and combined heat and orientation processing affect the transport properties of glassy polymers. Especially when crystallites are present, the effects can become surprisingly large. As noted for rubbery semicrystalline materials, the obvious improvements in barrier properties associated with organization of lamellar crystalline domains with their platelets perpendicular to the direction of penetrant flow can produce significant... 

The pressure at which plasticizing effects begin to overcome permeability depression depends primarily on the ratio of the partial pressure of the penetrant in the feed stream to the corresponding vapor pressure of the penetrant at the system temperature. As the pressure approaches the vapor pressure, solubility tends to increase rapidly, thereby inducing plasticization or clustering responses such as those already discussed for rubbery polymers. Even below the plasticization point, additional complexities not encountered with rubbery polymers are often observed in glassy materials. For example, low vapor pressure components such as water can cause depression of the permeability of other gases when water is... 

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