Switchable pH-Responsive Polymeric Membranes Prepared via Block Copolymer Micelle Assembly

Abstract

A process is described to manufacture monodisperse asymmetric pH-responsive nanochannels with very high densities (pore density >2 × 10(14) pores per m(2)), reproducible in m(2) scale. Cylindric pores with diameters in the sub-10 nm range and lengths in the 400 nm range were formed by self-assembly of metal-block copolymer complexes and nonsolvent-induced phase separation. The film morphology was tailored by taking into account the stability constants for a series of metal-polymer complexes and confirmed by AFM. The distribution of metal-copolymer micelles was imaged by transmission electron microscopy tomography. The pH response of the polymer nanochannels is the strongest reported with synthetic pores in the nm range (reversible flux increase of more than 2 orders of magnitude when switching the pH from 2 to 8) and could be demonstrated by cryo-field emission scanning electron microscopy, SAXS, and ultra/nanofiltration experiments.

Biomimetic block copolymer particles with gated nanopores and ultrahigh protein sorption capacity

“…The carboxylic acid units were deprotonated at high pH and the PAA segments stretched to minimize the charge repulsion, transforming the pore into a pH-sensitive gate without affecting the overall spherical shape of the particle. The effect is opposite to that observed in recently reported stimuli-responsive PS-b-P4VP isoporous membranes 36,37 .…”

Block Copolymer Membranes for Aqueous Solution Applications

“…Only years after the first report the method could be reproduced with different copolymer batches and solvents then with better understanding of how the morphology develops. By using field emission scanning microscopy, focus ion beam and cryo transmission electron microscopy 61,111 we claimed for the first time that the micelle formation in solution is essential for the membrane formation in this case. Later this has been recognized by other excellent groups in the field 112 .…”

“…Their presence and assembly in the solution bulk before casting has been directly confirmed by cryo transmission (TEM) and scanning electron (SEM) microscopy 62,99,111,117,118 and small angle x-ray scattering (SAXS) of the casting solution 99,113,114 . Indications that the micelle structures remain as part of the ordered top layer of the membrane were presented by different groups 61,111,112 , using scanning (SEM) or transmission (TEM) electron microscopy, with tomography, scanning transmission electron microscopy (STEM) and focus ion beam (FIB). It is important to mention that the block copolymer assembly in solution is very sensitive to concentration and solvent quality.…”

Ferrocene-Modified Block Copolymers for the Preparation of Smart Porous Membranes

“…In the present study, this is the PHEMA and PHEMA-co-PFcMA block segment. For the SNIPS process, a 16 wt % block copolymer solution of a mixture of pure and functionalized block copolymer (1:1 or 2:1 wt %) consisting of THF/DMF/DOX (2:1:1 wt %) and 0.1 wt % CuCl2 as additive [45,60] was prepared and the viscous solution was casted on top of a nonwoven polymer support by a doctor blade with a gap height of 200 μm (see Experimental Section). THF and DOX are better solvents for the PS segment, whereas DMF is better for the PHEMA segment [47].…”

“…In the last decade, functional block copolymer filtration membranes attracted enormous attention because of their isoporous surface structure and capability for responsiveness stimulated by external triggers [34][35][36][37][38][39][40][41]. The most prominent and first block copolymer in this field is polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), which revealed tremendous potential for water purification and separation processes [42][43][44][45][46]. Quite recently, we reported on the preparation of the amphiphilic block copolymer polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) for the formation of integral asymmetric porous membranes featuring a high water flux [47].…”