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Polybenzimidazole is doped with aromatic polycarboxylic acids to form supramolecular assemblies achieving strong size-sieving ability and thus high H2/CO2 selectivity.

Two stage reactive polymer (TSRP) networks can be programmed with spatially varying heterogeneity, presenting a new way of designing material structure and controlling or enhancing properties.

Carbon molecular sieve (CMS) membranes prepared by carbonization of polymers containing strongly size-sieving ultramicropores are attractive for high-temperature gas separations. However, polymers need to be carbonized at extremely high temperatures (900° to 1200°C) to achieve sub-3.3 Å ultramicroporous channels for H 2 /CO 2 separation, which makes them brittle and impractical for industrial applications. Here, we demonstrate that polymers can be first doped with thermolabile cross-linkers before low-temperature carbonization to retain the polymer processability and achieve superior H 2 /CO 2 separation properties. Specifically, polybenzimidazole (PBI) is cross-linked with pyrophosphoric acid (PPA) via H bonding and proton transfer before carbonization at ≤600°C. The synergistic PPA doping and subsequent carbonization of PBI increase H 2 permeability from 27 to 140 Barrer and H 2 /CO 2 selectivity from 15 to 58 at 150°C, superior to state-of-the-art polymeric materials and surpassing Robeson’s upper bound. This study provides a facile and effective way to tailor subnanopore size and porosity in CMS membranes with desirable molecular sieving ability.

Mixed matrix materials (MMMs) hold great potential for membrane gas separations by merging nanofillers with unique nanostructures and polymers with excellent processability. In situ growth of the nanofillers is adapted to mitigate interfacial incompatibility to avoid the selectivity loss. Surprisingly, functional polymers have not been exploited to co-grow the nanofillers for membrane applications. Herein, in situ synergistic growth of crystalline zeolite imidazole framework-8 (ZIF-8) in polybenzimidazole (PBI), creating highly porous structures with high gas permeability, is demonstrated. More importantly, PBI contains benzimidazole groups (similar to the precursor for ZIF-8, i.e., 2-methylimidazole) and induces the formation of amorphous ZIFs, enhancing interfacial compatibility and creating highly size-discriminating bottlenecks. For instance, the formation of 15 mass% ZIF-8 in PBI improves H

The presence of surface patterns on separation membranes, when properly designed, can enhance the membrane performance by increasing the active surface area, tuning the surface wettability, and promoting mass transfer in the boundary layer. This work reports a new method of patterning microporous membranes, namely, lithographically templated thermally induced phase separation (lt-TIPS). Templated by surface-patterned elastomeric molds, the TIPS of poly (vinylidene fluoride) (PVDF) and tributyl O-acetylcitrate (ATBC) lead to successful pattern replication onto the PVDF membranes. We systematically examined the TIPS processing conditions, including PVDF/ATBC concentration (20 wt%, 25 wt% and 30 wt%) and quenching temperature (25 °C and 100 °C), on the fidelity of pattern replication, as well as structure and properties of the PVDF membranes. Experimental results show that lower solution concentration and direct quenching to 25 °C lead to higher fidelity of pattern replication. Lower concentration and higher quenching temperature result in membranes with larger pores and higher porosity. In comparison with non-patterned PVDF membranes, the patterned PVDF membranes display similar pore structures, mechanical characteristics and crystallinity. In contrast, the presence of the surface pattern significantly increases the water contact angle and pure water flux, as expected from the increase in active surface area. The work shows that lt-TIPS is an effective method for patterning membranes, complementary to existing imprinting and phase-inversion based methods.

Studies have been carried out to determine the influence of depths of cut of diamond grinding wheels on the wear of diamond abrasives and the material removal rate of silicon nitride during single pass grinding. The results suggest that there is an optimum depth of cut, which yields the greatest material removal rate. If the grinding depth is less than this optimum depth of cut, the grinding efficiency is low. If the grinding depth is larger than this optimum depth of cut, premature dulling of the diamond wheel occurs. Furthermore, some of the diamond abrasives break due to grain fracture, and the original sharp diamond abrasives become flat and smooth. As a result, the material removal rate of silicon nitride drastically decreases.