Postfunctionalization of Nanoporous Block Copolymer Membranes via Click Reaction on Polydopamine for Liquid Phase Separation

In this work, an azido-modified dopamine derivative was synthesized and subsequently used to postfunctionalize the surface of nanoporous poly­(styrene)-<i>block</i>-poly­(4-vinylpyridine) diblock copolymer membranes. On the basis of this layer a continuative modification was realized by performing a “Click” reaction, namely, the Cu­(I)-catalyzed 1,3-dipolar cycloaddition, with different alkynes. While the Click reaction was monitored by X-ray photoelectron spectroscopy, the morphology of the membranes in the different states of modification was examined with scanning electron microscopy and atomic force microscopy. The membrane properties were characterized by measurements of contact angle and clean water permeance, retention tests, and protein adsorption. Independent from the alkyne applied during the Click reaction, the clean water permeance is approximately 1200 L m^–2 bar^–1 h^–1 and therefore slightly below the permeance of the pristine membrane. While the sharp molecular weight cutoff of the pristine membrane and all modified membranes is similar, antifouling properties as studied on the interaction of two model proteins (bovine serum albumin, hemoglobin) with the membranes turned out to be best for the membranes modified with 1-nonyne

Evaporation-Induced Block Copolymer Self-Assembly into Membranes Studied by <i>in Situ</i> Synchrotron SAXS

Amphiphilic diblock copolymers can spontaneously form integral asymmetric isoporous membranes by evaporation-induced self-assembly. The critical structural evolution steps occur within the first hundred seconds after solvent casting. By using synchrotron X-ray scattering employing a specially designed solvent casting apparatus, we were able to follow the kinetics of the structural evolution <i>in situ</i>. At an initial time of 20 s after solvent-casting we observe the first structural features on length scales <i>d</i> of 30–70 nm, signaled by a weak maximum in the low-<i>q</i> region of the measured scattering curves. During the subsequent period the length scales increase continuously until after around 100 s they reach a plateau value <i>d</i>_∞ of 80–120 nm, the size depending on the molecular weight of the block copolymer. Interestingly, the time evolution of the characteristic length scales follow a simple exponential saturation curve for all block copolymers, irrespective of molecular weight, composition, and addition of ionic additives, in agreement with theoretical models on two-dimensional ordered block copolymer domain formation. In addition, we could show that immersion in water during solvent evaporation leads to a nearly instantaneous increase of the characteristic length scale to its plateau value. The addition of salts such as Cu²⁺ leads to compaction of the structures with smaller characteristic length scales, but still following the same kinetic evolution