THIN-FILM-COMPOSITE GAS SEPARATION MEMBRANES - ON THE DYNAMICS OF THIN-FILM FORMATION MECHANISM OF POROUS SUBSTRATES

A wide range of gas separations of interest in energy applications are carried out using membranes. Growing attention has been paid to the t echnology of making thin-film-composites(TFCs) membranes. Understandin g the polymer solution and substrate property is key to successfully p reparing TFCs membranes. This paper reports on some fundamental issues of coating hollow fibers with polymer from solution by dip coating. P olymeric porous hollow fibers with varying porosities and permeances w ere coated with polymer solutions of different viscosities in a contin uous process. In addition, the fibers were coated dry and by presoakin g in the coating solvent. It was found that the thickness of the coati ng on the low permeance/porosity/wet and dry fibers could be approxima ted by the Deryaguin model (h/R = 1.33 (Ca)(0.67)). For dry fibers, as the fiber porosity increased, the measured coating thickness was sign ificantly underestimated by the Deryaguin equation. It is believed tha t the pores in the fiber allow rapid capillary suction of the solvent into the fiber walls and the bore, thus increasing the solution viscos ity near the fiber wall, resulting in an increase in the coating thick ness. Significant differences in the rate of solvent uptake were obser ved in these fibers by wicking experiments on a microbalance to suppor t the above hypothesis.