The effect of lattice compressibility on the thermodynamics of gas sorption in polymers
An incompressible lattice model, Flory-Huggins theory, was used to model the sorption of carbon dioxide, methane, and ethylene in silicon rubber. Above the glass transition temperature, the criterion of lattice incompressibility was satisfied with physically-reasonable and constant values for the partial molar volumes (or lattice-site volumes) of the gases. Below the glass transition temperature, lattice incompressibility required concentration-dependent and physically-unrealistic values for the lattice-site volumes. Instead of forcing lattice incompressibility on the systems, an activity coefficient model based on a compressible lattice, the glassy polymer lattice sorption model (GPLSM) was developed. The GPLSM equation has four parameters: the Henry`s law coefficient and the interaction energies for the pure gas, the pure polymer, and the gas-polymer pair. The pure gas interaction energy is determined from an equation of state, and a geometric mean assumption is used for the gas-polymer interaction energy. The pure polymer segment-segment interaction energy and the Henry`s law constant remain as adjustable parameters. GPLSM, was used to analyze gas sorption in glassy polycarbonate (PC), tetramethyl-polycarbonate (TMPC), and hexafluoropolycarbonate (HFPC). Two adjustable parameters, the segment-segment interaction energy and the Henry`s law constant, were necessary to model CO{sub 2} sorption data in these polymers. The segment-segment interaction energy was then fixed and H was varied to model CH{sub 4}, and C{sub 2}H{sub 4} sorption in unconditioned PC, CO{sub 2}, CH{sub 4}, and C{sub 2}H{sub 4} sorption in CO{sub 2}-conditioned polycarbonate, and desorption hysteresis in PC, TMPC, and HFPC. Carbon dioxide sorption in conditioned polystyrene (PS) and poly[phenylene oxide] (PPO) was modeled with the two adjustable parameters described above. Carbon dioxide sorption in blends of PS and PPO was modeled using a single adjustable parameter, H.
- Research Organization:
- Johns Hopkins Univ., Baltimore, MD (United States)
- OSTI ID:
- 111311
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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