Computer simulation and experimental verification of morphology and gas permeability of poly(4-methyl-1-pentene) membranes: effects of polymer chain and diluent extractant

The effects of the polymer chain topology and choice of diluent extractant on the pore morphology and gas diffusion coefficient of poly(4-methyl-1-pentene) (PMP) membranes fabricated by thermally induced phase separation (TIPS) were investigated using 3-D dissipative particle dynamics and molecular dynamics simulation, taking dioctyl phthalate as the diluent into account. The dynamics simulation data indicate that the branched and crosslinked PMP chains are more inclined to form larger pore structures in the PMP support layer than the linear counterparts. The longer PMP chains also tend to generate larger pore structures. Further, the diffusivity coefficient of the dense PMP skins composed of branched and crosslinked PMP chains was smaller than those composed of the linear congeners, and the diffusivity coefficient was larger for the dense PMP skins from polymers with a shorter chain length. Moreover, ethanol and acetone as extractants exerted great influence on the membrane structure during the diluent extraction process, introducing further non-solvent phase separation and eliminating pore collapse. To verify the simulation predictions, asymmetric PMP hollow fiber membranes were fabricated via TIPS. The effects of the molecular weight of PMP and the diluent extractants were studied. The experimentally observed membrane morphologies and gas permeability were analyzed and discussed. The experimental results are all consistent with the corresponding simulation trends. The findings prove that the dynamics simulation method is promising for providing fabrication guidelines for the design of gas-diffusive membranes, especially in terms of rational selection of the polymer chain topology and diluent extractant.