Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Abstract

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20-40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by 2 scanning electronic microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.

Block Copolymer Membranes for Aqueous Solution Applications

“…Additionally to the flat-sheet configuration, hollow fibers are frequently used in large membrane applications such as artificial kidney. The manufacture of block copolymer membranes in hollow fiber geometry has been demonstrated by our group 138,139 and by Radjabian et al 146 . In summary as long as the desired block copolymers is available with narrow molecular weight distribution in large amount and at reasonable cost scaling up is not a problem.…”

Influence of block sequence and molecular weight on morphological, rheological and dielectric properties of weakly and strongly segregated styrene-isoprene triblock copolymers

“…They exhibit particular properties which are caused by the combination of different blocks most often leading to self-assembled periodic microphase separated structures. The application of block copolymers in modern material science varies from blends [5][6][7][8][9][10][11][12], nanopatterning [13][14][15][16][17][18] to membranes [19][20][21][22][23][24][25][26][27].…”

Functional Macromolecular Systems: Kinetic Pathways to Obtain Tailored Structures

“…Also morphological transitions can result from the action of external fields, like the transformation of spherical into cylindrical microdomains in bulk or solution . Processing techniques like spinning of fibers or hollow fibers from solution are still poorly understood. Electrospinning is a special spinning technique which leads to fibers with diameters down to the nanometer range .…”