Dissipative particle dynamics study and experimental verification on the pore morphologies and diffusivity of the poly (4-methyl-1-pentene)-diluent system via thermally induced phase separation: The effect of diluent and polymer concentration

Abstract

Dissipative particle dynamics (DPD) simulation was performed to construct the mesophase membrane morphologies of poly(4-methyl-1-pentene) (PMP) during thermally induced phase separation (TIPS). The PMP morphologies and their fluid diffusivities relationship was established using a mesoscale 3-D tetragonal-like structure construction. The effects of PMP concentration and the use of a single diluent (dioctyl phthalate, diphenyl ether, and dibutyl phthalate) or a mixed diluent on the pore morphology were compared. The diffusivity resistance was evaluated by comparing the mean square displacement of a hypothetical fluid bead through tetragonal-like morphologies in three normal directions. The 3-D morphology and density profile results revealed that larger pores were produced after TIPS when the PMP-diluent interaction was weaker. Radial distribution function analysis showed that poor diluent and high PMP concentration could form a coarsened structure with less interconnectivity, indicating more diffusion resistance. To verify DPD simulation results, PMP hollow fibre membranes (HFMs) were fabricated via TIPS, and HFM cross-sectional morphologies proved that the pore structures agreed with the DPD-simulation 3-D evolution diagram. The structure-fluid diffusivity resistance relationship was also confirmed by porosity measurements and gas permeation testing. The DPD simulation method is promising for the fabrication and design of gas-diffusive membranes, especially in terms of the rational selection of diluent and polymer concentration.