Thin-Film-Composite Gas Separation Membranes: On the Dynamics of Thin Film Formation Mechanism On Porous Substrates

Abstract

A wide range of gas separations of interest in energy applications are carried out using membranes. Growing attention has been paid to the technology of making thin-film-composites(TFCs) membranes. Understanding the polymer solution and substrate property is key to successfully preparing TFCs membranes. This paper reports on some fundamental issues of coating hollow fibers with polymer from solution by dip coating. Polymeric porous hollow fibers with varying porosities and permeances were coated with polymer solutions of different viscosities in a continuous process. In addition, the fibers were coated dry and by presoaking in the coating solvent. It was found that the thickness of the coating on the low permeance/porosity/wet and dry fibers could be approximated by the Deryaguin model (h/R = 1.33 (Ca) ^0.67). For dry fibers, as the fiber porosity increased, the measured coating thickness was significantly underestimated by the Deryaguin equation. It is believed that the pores in the fiber allow rapid capillary suction of the solvent into the fiber walls and the bore, thus increasing the solution viscosity near the fiber wall, resulting in an increase in the coating thickness. Significant differences in the rate of solvent uptake were observed in these fibers by wicking experiments on a microbalance to support the above hypothesis.