Stochastic reconstruction of mixed-matrix membranes and evaluation of effective permeability

Microstructures of three mixed-matrix membrane samples made of polyimide and silicalite-1 particles were reconstructed using a stochastic reconstruction procedure. The samples differed in the volume fractions of silicalite-1 particles as follows: 0.166, 0.310 and 0.371. The reconstruction revealed the existence of percolation clusters of silicalite-1 particles in the two samples with the volume fraction of silicalite-1 greater than 0.3. In contrast, only the reconstructed microstructure of the first sample contained small clusters of silicalite-1 particles, which did not percolate along any direction. The results of this reconstruction were tested by simulating the random walk of CO2 molecules in the reconstructed bodies and by predicting the effective permeability of CO2. Both original and reconstructed membranes revealed a similar enhanced effective permeability, which exceeded predictions based on the effective medium approximations. Therefore, we suggest that clustering of the silicalite-1 particles was the primary cause of the permeability increase.