Tailoring pore size of ultrafiltration membranes all the way down toward the nanofiltration regime in a predictable manner from molecular design principles is highly desirable. Here we present a way to achieve this in surface separation layers of nonsolvent induced phase separation (NIPS) derived graded block copolymer (BCP) membranes by means of an organic additive. Glycerol, a nontoxic organic molecule, is incorporated at varying amounts into poly(isoprene-b-styrene-b-4-vinylpyridine) (ISV) triblock terpolymer casting solutions. Employing scanning electron microscopy image analysis and solute rejection tests on resulting membranes, the relationship between the amount of additives and membrane performance (permeability, selectivity) is established. Pore size increases from 23 to 48 nm are achieved by moving from membranes cast from pure ISV solutions to those cast from up to 40% weight (relative to ISV) glycerol containing solutions. It is then demonstrated how a combination of additive driven pore expansion in conjunction with P4VP chain stretching via charge repulsion can be used to reduce pore sizes down to 5 nm under acidic (pH 3.6) conditions. This provides a path to move from ultrafiltration toward nanofiltration applications for asymmetric BCP membranes without compromising membrane mechanical properties. It also enables production of advanced membranes with wide tunability, low cost, and high performance.

A facile method for forming asymmetric organic-inorganic hybrid membranes for selective separation applications is developed. This approach combines co-assembly of block copolymer (BCP) and inorganic nanoparticles (NPs) with non-solvent induced phase separation. The method is successfully applied to two distinct molar mass BCPs with different fractions of titanium dioxide (TiO2) NPs. The resulting hybrid membranes exhibit structural asymmetry with a thin nanoporous surface layer on top of a macroporous fingerlike support layer. Key parameters that dictate membrane surface morphology include the fraction of inorganics used and the length of time allowed for surface layer development. The resulting membranes exhibit both good selectivity and high permeability (3200 ± 500 Lm(-2) h(-1) bar(-1)). This fast and straightforward synthesis method for asymmetric hybrid membranes provides a new self-assembly platform upon which multifunctional and high-performance organic-inorganic hybrid membranes can be formed.

Selective degradation of block copolymer templates and backfilling the open mesopores is an effective strategy for the synthesis of nanostructured hybrid and inorganic materials. Incorporation of more than one type of inorganic material in orthogonal ways enables the synthesis of multicomponent nanomaterials with complex yet well-controlled architectures; however, developments in this field have been limited by the availability of appropriate orthogonally degradable block copolymers for use as templates. We report the synthesis and self-assembly into cocontinuous network structures of polyisoprene-block-polystyrene-block-poly(propylene carbonate) where the polyisoprene and poly(propylene carbonate) blocks can be orthogonally removed from the polymer film. Through sequential block etching and backfilling the resulting mesopores with different metals, we demonstrate first steps toward the preparation of three-component polymer–inorganic hybrid materials with two distinct metal networks. Multiblock copolymers in which two blocks can be degraded and backfilled independently of each other, without interference from the other, may be used in a wide range of applications requiring periodically ordered complex multicomponent nanoarchitectures.

Evaporation-induced asymmetric triblock terpolymer membrane formation from polyisoprene-block-polystyrene-block-poly­(4-vinyl­pyridine) (ISV) that relies on self-assembly of doctor bladed solutions was studied using in situ grazing incidence small-angle X-ray scattering (GISAXS). Transient ordered structures were observed for two ISV terpolymers at intermediate evaporation times in the top surface layers of the films as a function of molar mass and solution concentration. Analysis of the GISAXS patterns revealed the evolution from disordered to ordered structures including a transition from body-centered cubic (BCC) to simple cubic (SC) lattices and finally to an amorphous mesoscale structure. The BCC to SC transition solves an apparent structural puzzle resulting from comparisons of, on one side, earlier quiescent solution SAXS studies suggesting BCC terpolymer micelle structures at higher concentrations and, on the other side, electron microscopy studies consistent with SC lattices originating from polymer micelles in the top separation layer of asymmetric ISV membranes. Gaining insights into the structural evolution of asymmetric triblock terpolymer film formation may enable further optimization of self-assembly plus non-solvent-induced phase separation (SNIPS) based high performance isoporous asymmetric block copolymer ultrafiltration membranes.

Block copolymer (BCP) self-assembly is a promising route to manufacture functional nanomaterials for applications from nanolithography to optical metamaterials. Self-assembled cubic morphologies cannot, however, be conveniently optically characterized in the lab due to their structural isotropy. Here, the aligned crystallization behavior of a semicrystalline-amorphous polyisoprene-b-polystyrene-b-poly(ethylene oxide) (ISO) triblock terpolymer was utilized to visualize the grain structure of the cubic microphase-separated morphology. Upon quenching from a solvent swollen state, ISO first self-assembles into an alternating gyroid morphology, in the confinement of which the PEO crystallizes preferentially along the least tortuous pathways of the single gyroid morphology with grain sizes of hundreds of micrometers. Strikingly, the resulting anisotropic alignment of PEO crystallites gives rise to a unique optical birefringence of the alternating gyroid domains, which allows imaging of the self-assembled grain structure by optical microscopy alone. This study provides insight into polymer crystallization within a tortuous three-dimensional network and establishes a useful method for the optical visualization of cubic BCP morphologies that serve as functional nanomaterial templates.