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 T
g, 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.
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