The Effect of Pore Penetration on Composite Membranes

Composite membranes typically consist of at least one nonporous layer on top of a porous structure. The porous support restricts diffusion in the top layer because molecules can exit the layer only where a pore is present. Computational fluid dynamics (CFD) has been used to simulate the geometric restriction and an empirical model was developed to quantify the effect of the porous support on the permeance of composite membranes.

In this work, modeling results are compared to experimental data for composite membranes consisting of a dense polydimethylsiloxane (PDMS) layer on a polyetherimide (PEI) ultrafiltration support. Significant discrepancies are observed between the experimental and modeling results. Pore penetration is believed to be a likely reason for the difference between the theoretical and measured permeances. A resistance-in-series model and CFD were employed to calculate the effect of pore penetration on the permeance of composite membranes. Results from these two approaches are in good agreement, and provide a good fit to experimental composite membrane data if pore penetration depth is allowed to vary. An analysis of the PDMS/PEI composite membrane data, suggests that the depth of PDMS penetration into the PEI pores increases as the thickness of the PDMS selective layer increases.