Fabrication of polydimethylsiloxane (PDMS) dense layer on porous polyethersulfone (PES) hollow fibre membrane with varying dip coating parameters

Abstract

Polydimethylsiloxane (PDMS) is commonly used as a separating layer in gas separation membrane, hydrocarbon separation process, pervaporation and as a viable gutter layer in composite membrane fabrication. A methodical dip coating technique was used to fabricate PDMS dense layer on porous polyethersulfone (PES) hollow fibre membrane. Dip coating parameters such as coating speed (5-15 mm s -1 ) and holding time (10-900 s) were varied using an automated dip coating machine. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy characterisation were also conducted to investigate the membrane morphology and confirmed the presence of a coating on the membrane surface. Gas permeation performance test was carried out with CO 2 and N 2 under transmembrane pressure of 1 to 3 bars after membrane coating was finalised. The test results indicated that the coating speed inflicted less influence in the overall performance with a selectivity of 0.86. Gas permeance also exceeded 20,000 GPU mark at a lower speed, suggesting that a single coating at this speed range could not fully coat the porous PES fibres. Nevertheless, reduction of permeance with increasing speed indicates an improvement in the PDMS layer thickness. On the other hand, holding time in the coating solution showed a slight effect on membrane performance compared to the coating speed. However, the membrane exhibits drop in permeance reaching below 1,000 GPU at high holding time, suggesting a more complete coverage of the support with the PDMS layer. Hypothetically, it is caused by the increased viscosity during the PDMS crosslinking reaction as time passed, allowing more PDMS solution to be retained on the PES fibre's surface.