Component mobility analysis in the membrane-forming system water/ n-methyl-2-pyrrolidone/polyethersulfone

Abstract

Component mobilities (diffusion coefficients) were evaluated in the membrane-forming system water- N-methyl-2-pyrrolidone-polyethersulfone (H 2O(1)-NMP(2)-PES(3)). Two types of solvent-nonsolvent binary diffusion coefficients were obtained. In the 1-2 binary mixture D 12=5-7X10 −6 cm 2/sec. In agreement with observations of other authors, macromolecular diffusion coefficients measured by quasi-elastic light scattering (QELS) were found to exhibit anisotropy in semidilute and concentrated solutions. In the 2-3 binary, fast mode coefficients were: D C 23=3-7X10 −7 cm 2/sec and the slow mode coefficients were: D CM 23=3X10 −9-8X10 −12 cm 2/sec. Fast and slow QELS modes were identified with cooperative (C) and center-of-mass (CM) motions of polymer chains, respectively. Friction factors were calculated for both modes. Concentration dependence of friction factors was found to be strikingly different for the two modes. In ternary mixtures, the fast-mode mobility was found to decrease with nonsolvent concentration, while the slow mode (where detectable) was unaffected by addition of nonsolvent. Mobility of PES in other solvent and nonsolvent systems was also investigated.