Carbon Dioxide Solubility in Three Fluorinated Polyimides Studied by Molecular Dynamics Simulations

Abstract

Fluorinated polyimides are interesting polymer materials for gas separation applications because of their good mechanical, thermal, and transport properties. We have performed molecular dynamics simulations (MD) of CO2 sorption and desorption in three fluorinated polyimides: 6FDA-6FpDA, 6FDA-6FmDA, and 6FDA-DAM. These polyimides are known to vary significantly in their gas permeation properties. A stepwise procedure was used to insert CO2 molecules into the previously prepared polymer matrices in order to mimick the experimental procedure of progressive loading and to avoid the necessity of preswelling the samples. An iterative technique was then used to estimate the vapor pressure of CO2 that would have to be applied in order to obtain the imposed uptake. The resulting sorption isotherms are found to be in relatively good agreement with their respective experimental curves, and the trend in solubility was reproduced (6FDA-DAM > 6FDA-6FpDA > 6FDA-6FmDA). Desorption isotherms were also calculated starting from systems corresponding to an applied pressure of 60 bar. Hysteresis was evident even upon immediate unloading. Changes in volume, void space, potential energies, etc., have been characterized and compared to experimental data and to theories of gas sorption and plasticization in glassy polymers.

Parameterization of electrostatic interactions for molecular dynamics simulations of heterocyclic polymers

“…As it was mentioned above in the Introduction, a correct account for EI within atomistic force fields in the MD method is, nowadays, a nontrivial task due to the impossibility of a direct comparison of calculated partial atomic charges with experimental data . Partial atomic charges are calculated by means of quantum‐chemical methods from electronic orbital populations or electrostatic surface potential (ESP) and used further in MD force fields …”

“…Molecular dynamics (MD) simulations represent an efficient alternative to chemical syntheses, making it possible to reduce both time and material resources and not only to interpret experimental investigation results at the molecular level but also to predict properties of novel polymer compounds before their synthesis. Furthermore, the MD method implemented into fully atomic models allows the effect of slight changes in the chemical structure of bulk PIs to be taken into account in order to optimize the performance of polyimide‐based materials …”

“…In a number of studies, thermal properties of PIs are simulated with the use of force fields of the TRIPOS family . For each individual compound, the values of partial atomic charges are calculated by density functional theory (DFT) or Hartree‐Fock ( ab initio ) methods.…”

Improved gas selectivity of polyetherimide membrane by the incorporation of PIM polyimide phase

“…The structure of the 80/20 polymer matrix saturated by CO 2 sorption may retard a little the passage of the gas across the membrane due to the interaction between gas molecule and polymer segments. [64][65][66] Despite blend membrane at a ratio of 50/50 was proved to present stronger molecular interactions as well as lower d-spacing, typical high permeability and low selectivity of microporous phase predominated and consequently, it was responsible for the low gas separation performance of this membrane. Figures 7 and 8 depict upper bound graphics of Robeson for H 2 /CO 2 and O 2 /N 2 , respectively.…”

Thermodynamic transferability of coarse-grained potentials for polymer–additive systems

“…This may be related to geometric aspects of the mapping scheme that we employed. However, to address these questions, a systematic study of a single system with different CG mapping schemes is required where enthalpy-entropy compensation of implicit entropy contributions to the effective interaction potentials is studied in greater detail (see discussion of eqn (2) and (3) in Section 2.3).…”