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Gas sorption isotherms in swelling glassy polymers - detailed atomistic simulations

 
: Hölck, Ole; Böhning, Martin; Heuchel, Matthias; Siegert, Martin R.; Hofmann, Dieter

:

Journal of membrane science 428 (2013), S.523-532
ISSN: 0376-7388
ISSN: 1873-3123
Deutsche Forschungsgemeinschaft DFG
Bo 1921/1-2
Deutsche Forschungsgemeinschaft DFG
Bo 1921/1-3
Deutsche Forschungsgemeinschaft DFG
He2108/2-1
Deutsche Forschungsgemeinschaft DFG
He2108/2-3
Englisch
Zeitschriftenaufsatz
Fraunhofer IAP ()
Fraunhofer IZM ()

Abstract
Detailed atomistic simulations were carried out for swelling polymer/gas systems related to experimental sorption and dilation data for CO2 and CH4 in three glassy polymers (polysulfone PSU, the polyimide 6FDA-TrMPD, and a polymer of intrinsic microporosity PIM-1) at 308 K (35 °C) and pressures up to 50 bar. Corresponding experiments were performed with a gravimetric sorption balance and a dilatometer based on a capacitance distance sensor. For each polymer/gas system molecular packing models were prepared and equilibrated for two reference states: the pure polymer is taken as reference for the respective "unswollen" state and similarly the state of the highest penetrant pressure reached in the corresponding experiment is taken to represent the "swollen" state. Models for the latter were constructed in agreement with experimental data (pressure, temperature, gas concentration and volume dilation). Concentration-pressure isotherms of each polymer/gas system were obtained using Grand Canonical Monte Carlo (GCMC) simulations for both reference states (depleted of gas molecules), which are in good agreement with the experimental data in the respective pressure range. As expected these isotherms - due to the simulation technique used, merely based on hole-filling in a static host matrix - do not represent the sorption behavior over a broader range of gas pressures which may involve significant structural rearrangements as well as swelling and relaxational phenomena. Nevertheless, a linear combination of the two GCMC-isotherms allows the interpolation in order to describe the nonlinear gas sorption in the glassy polymers under investigation covering the penetrant pressure range between the reference states in good agreement with the experimental results.

: http://publica.fraunhofer.de/dokumente/N-233386.html