Yun-Hsuan Huang

Mixed matrix membranes with molecular-interaction-driven tunable free volumes for efficient bio-fuel recovery

Mixed matrix membranes (MMMs), consisting of inorganic fillers dispersed in a polymer matrix, are regarded as one of the most promising futuristic membranes. This work reports the utilization of molecular interactions to finely control the conformation and topology of polymer chains to fabricate high-performance polyhedral oligomeric silsesquioxanes (POSS)/polydimethylsiloxane (PDMS) MMMs. The influence of the incorporation of POSS on the polymer structure was systematically studied by molecular dynamics simulations combined with DSC, XRD and IR measurements. The surface and interfacial morphologies of the MMMs were observed through SEM, TEM and AFM characterizations. In particular, positron annihilation spectroscopy was employed to analyze the evolution of free volumes in the MMMs. Results indicated that facilely incorporating POSS into PDMS by molecular interactions could manipulate favorable interfacial morphology and tunable free volumes in MMMs. In the PDMS MMMs, the small free volumes were reduced and the large free volumes increased; these changes were beneficial for the preferential permeation of large-sized molecules through the polymeric membrane. As applied to the bio-butanol recovery from aqueous solutions, the prepared POSS/PDMS MMMs exhibited a simultaneous increase in permeability and selectivity, breaking the permeability-selectivity trade-off limitation, moreover transcending the upper bound of the state-of-the-art organophilic pervaporation membranes. Therefore, our work demonstrates that the proposed approach based on rationally creating molecular interactions can be expected to have broad applicability in fabricating high-quality MMMs for molecular separations.

Novel thermally stable and soluble triarylamine functionalized polyimides for gas separation

A novel series of solution-processable aromatic polyimide membranes with trimethyl-substituted triphenylamine units for gas separation were prepared from a newly synthesized dianhydride, N,N-bis(3,4-dicarboxyphenyl)-2,4,6-trimethylaniline dianhydride (2), and various diamines via one-step high-temperature solution polymerization. The corresponding polyimides derived from structurally related dianhydrides with different pendant groups such as phenyl, naphthyl, and pyrenyl moieties were also prepared for comparison. All the polyimides were readily soluble in many polar solvents and showed useful levels of thermal stability associated with high glass-transition temperatures (Tg, 324–455 °C) and high char yields (higher than 58% at 800 °C in nitrogen). The noncoplanar triphenylamine-containing polyimides IV with pendant trimethyl-phenyl moieties exhibited an effective improvement of gas permeability with a minor decrease in permselectivity.

Effect of the surface property of poly(tetrafluoroethylene) support on the mechanism of polyamide active layer formation by interfacial polymerization

The mechanism of polyamide formation by interfacial polymerization is important fundamental knowledge for understanding the properties of the polyamide active layer of thin-film composite (TFC) membranes. In this study, TFC membranes of polyamide using poly(tetrafluoroethylene) (PTFE) as the support were prepared by interfacial polymerization. The effect of the surface property of the PTFE membrane support on the mechanism of formation of the polyamide active layer was investigated. Characterization of polyamide–PTFE composite membranes was performed by attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. Positron annihilation spectroscopy was used to analyze the microstructural variation in the polyamide active layer. The growth of the polyamide film was affected by the surface property of the PTFE support. Positron annihilation lifetime spectroscopy (PALS) results showed that the densest structure was at the interface between the polyamide layer and the PTFE support for the polyamide–hydrophilic PTFE composite membrane system; however, the densest structure was at the top surface of the polyamide active layer for the polyamide–hydrophobic PTFE composite membrane system. The high electronegativity of the –CF2– groups on the PTFE support caused “quenching” and “inhibition” effects, resulting in a dramatic decrease in the o-Ps intensity.