Thermally and Chemically Stable Isoporous Block Copolymer Membranes

Ultrafiltration (UF) membranes, particularly membranes fabricated from self-assembled diblock copolymers, hold promise in wastewater treatment, dairy, and food industries. Membrane development goals involve combining a highly porous selective layer with a narrow pore size distribution with a mechanically stable supporting layer to achieve constant flux. To date, isoporous integral asymmetric membranes have been formed either as flat sheets or hollow fibers, and a surface-selective layer determines membrane separation performance. A unique isoporous membrane of the poly(4-vinylbenzocyclobutene)-b-poly(4-vinylpyridine) (PVBCB-b-P4VP) diblock copolymer with a substructure of almost homogeneous porosity throughout the body of the material (three-dimensional porosity) has been developed. Moreover, the matrix of the membrane (PVCB) enables it to undergo cross-linking, allowing the membrane to be thermally sterilized and applied in high-temperature UF applications

Continuous Equilibrated Growth of Ordered Block Copolymer Thin Films by Electrospray Deposition

Deposition of block copolymer thin films is most often accomplished in a serial process where material is spin coated onto a substrate and subsequently annealed, either thermally or by solvent vapor, to produce a well-ordered morphology. Here we show that under appropriate conditions, well-ordered block copolymer films may be continuously grown under substrate equilibrated conditions by slow deposition of discrete subattoliter quantities of material using electrospray. We conduct time-resolved observations and investigate the effects of process parameters that underpin film morphology including solvent selectivity, substrate temperature, block-substrate selectivity, and flow rate of the feed solution. For a PEO cylinder-forming poly(styrene-b-ethylene oxide) block copolymer, we uncover a wide temperature window from 90 to 150 °C and an ideal flow rate of 2 μL/min for ordered film deposition from dilute acetone solutions. PEO cylinders aligned with their long axes perpendicular to the film–air interface at optimal spray conditions. Using poly(styrene-b-methyl methacrylate) deposited onto neutrally selective surfaces, we show that the substrate-equilibrated process results in vertically oriented microdomains throughout the film, indicating a preservation of the initial substrate-dictated morphology during the film deposition. Electrospray offers a new and potentially exciting route for controlled, continuous growth of block copolymer thin films and manipulation of their microstructure

Nanocomposites of Polystyrene‑<i>b</i>‑Poly(isoprene)‑<i>b</i>‑Polystyrene Triblock Copolymer with Clay–Carbon Nanotube Hybrid Nanoadditives

Polystyrene-<i>b</i>-polyisoprene-<i>b</i>-polystyrene (PS-<i>b</i>-PI-<i>b</i>-PS), a widely used linear triblock copolymer of the glassy-rubbery-glassy type, was prepared in this study by anionic polymerization and was further used for the development of novel polymer nanocomposite materials. Hybrid nanoadditives were prepared by the catalytic chemical vapor deposition (CCVD) method through which carbon nanotubes were grown on the surface of smectite clay nanolayers. Side-wall chemical organo-functionalization of the nanotubes was performed in order to enhance the chemical compatibilization of the clay–CNT hybrid nanoadditives with the hydrophobic triblock copolymer. The hybrid clay–CNT nanoadditives were incorporated in the copolymer matrix by a simple solution-precipitation method at two nanoadditive to polymer loadings (one low, i.e., 1 wt %, and one high, i.e., 5 wt %). The resulting nanocomposites were characterized by a combination of techniques and compared with more classical nanocomposites prepared using organo-modified clays as nanoadditives. FT-IR and Raman spectroscopies verified the presence of the hybrid nanoadditives in the final nanocomposites, while X-ray diffraction and transmission electron microscopy proved the formation of fully exfoliated structures. Viscometry measurements were further used to show the successful incorporation and homogeneous dispersion of the hybrid nanoadditives in the polymer mass. The so prepared nanocomposites exhibited enhanced mechanical properties compared to the pristine polymer and the nanocomposites prepared by conventional organo-clays. Both tensile stress and strain at break were improved probably due to better interfacial adhesion of the clay–CNT hybrid of the flexible rubbery PI middle blocks of the triblock copolymer matrix

Effect of Chain Architecture on the Compatibility of Block Copolymer/Nanoparticle Blends

The effect of block copolymer chain connectivity on the structure formation in binary blends comprising block copolymer hosts and enthalpically neutralized particle fillers is investigated for linear diblock (AB) and triblock (ABA and BAB) as well as four-arm star copolymer architectures (AB3 and A3B). For particles with approximately constant effective size (defined here as the ratio of filler particle diameter to host polymer radius of gyration), miscibility was observed only within diblock copolymers and within the domains formed by the end blocks of triblock copolymers. The limitation of particle miscibility within the triblock mid-domain is interpreted as a consequence of the entropy loss associated with particle deposition due to the stretched configuration of bridged midblock chains. Particle aggregation was observed in both star copolymer samples irrespective of the architecture of the particle-loaded polymer domain. In the case of particle loading of the branched copolymer domain, this is rationalized as a consequence of the increased effective particle size, whereas the incompatibility of particle fillers in the linear block domain of miktoarm copolymer hosts is interpreted as a result of the coupling of dimensional changes within the microstructure along with the reduced axial compressibility of the particle-free branched domain. The sensitive dependence of the particle compatibility on the chain architecture of the polymer host illustrates a yet unexplored parameter space that will need to be taken into account if particle blends are to be designed with branched or multiblock host copolymer architectures