Wei-Song Hung

Tuning nanostructure of graphene oxide/polyelectrolyte LbL assemblies by controlling pH of GO suspension to fabricate transparent and super gas barrier films

A technique of layer-by-layer (LbL) self-assembly was used to prepare transparent multilayered gas barrier films consisting of graphene oxide (GO)/branched poly(ethylenimine) (BPEI) on a poly(ethylene terephthalate) substrate. The effect of the GO suspension pH on the nanostructure and oxygen barrier properties of the GO/BPEI film was investigated. The oxygen barrier properties of the assemblies were shown to be highly dependent on the pH. It was demonstrated that the film assemblies prepared using a GO suspension with a pH of 3.5 exhibited very dense and ordered structures and delivered very low oxygen transmission rates (the lowest was <0.05 cm(3) m(-2) day(-1)). The assemblies were characterized with ultraviolet-visible spectroscopy and ellipsometry to identify the film growth mechanism, and the result indicated a linear growth behavior. To analyze the nanostructure of the films, atomic force microscopy, transmission electronic microscopy, and grazing incidence wide-angle X-ray diffraction were used.

Bio-inspired fabrication of high perm-selectivity and anti-fouling membranes based on zwitterionic polyelectrolyte nanoparticles

Nanofiltration membranes featuring high permeability, selectivity and anti-fouling properties represent a focal point of advanced membrane technologies for clean water production and purification. Inspired by “water channel” structures and fouling resistance characteristics of biological membranes, we fabricated a novel thin-film nanocomposite (TFN) membrane containing zwitterionic polyelectrolyte nanoparticles (ZPNPs) by interfacial polymerization, wherein ZPNPs act as building blocks allowing for simultaneously improved permeability, selectivity and anti-fouling properties. By modulating the zwitterionic group content and ionic cross-linking degree of ZPNPs, the TFN-ZPNP membrane showed high water permeability (109.7 L m−2 h−1 MPa−1) and enhanced NaCl/Na2SO4 selectivity (28.4), respectively; these values were 191% and 125% of those for the pristine polyamide membrane. It was also demonstrated that the incorporation of ZPNPs can increase the surface hydrophilicity, electronegativity and reduce the surface roughness, leading to an improved anti-fouling performance against the bovine serum albumin protein foulant.

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.

Preparation and Characterization of Bioplastic-Based Green Renewable Composites from Tapioca with Acetyl Tributyl Citrate as a Plasticizer

Granular tapioca was thermally blended with poly(lactic acid) (PLA). All blends were prepared using a plasti-corder and characterized for tensile properties, thermal properties and morphology. Scanning electron micrographs showed that phase separation occurred, leading to poor tensile properties. Therefore, methylenediphenyl diisocyanate (MDI) was used as an interfacial compatibilizer to improve the mechanical properties of PLA/tapioca blends. The addition of MDI could improve the tensile strength of the blend with 60 wt% tapioca, from 19.8 to 42.6 MPa. In addition, because PLA lacked toughness, acetyl tributyl citrate (ATBC) was added as a plasticizer to improve the ductility of PLA. A significant decrease in the melting point and glass-transition temperature was observed on the basis of differential scanning calorimetry, which indicated that the PLA structure was not dense after ATBC was added. As such, the brittleness was improved, and the elongation at break was extended to several hundred percent. Therefore, mixing ATBC with PLA/tapioca/MDI blends did exhibit the effect of plasticization and biodegradation. The results also revealed that excessive plasticizer would cause the migration of ATBC and decrease the tensile properties.

Multilayered poly(vinylidene fluoride) composite membranes with improved interfacial compatibility: correlating pervaporation performance with free volume properties.

A spin-coating process integrated with an ozone-induced graft polymerization technique was applied in this study. The purpose was to improve the poor interfacial compatibility between a selective layer of poly(2-hydroxyethyl methacrylate) (PHEMA) and the surface of a poly(vinylidene fluoride) (PVDF) substrate. The composite membranes thus fabricated were tested for their pervaporation performance in dehydrating an ethyl acetate/water mixture. Furthermore, the composite membranes were characterized by field emission scanning electron microscopy (FE-SEM) for morphological change observation and by Fourier transform infrared spectroscopy equipped with attenuated total reflectance (ATR-FTIR) for surface chemical composition analysis. Effects of grafting density and spin-coating speed on pervaporation performance were examined. The composite membrane pervaporation performance was elucidated by means of free volume and depth profile data obtained with the use of a variable monoenergy slow positron beam (VMSPB). Results indicated that a smaller free volume was correlated with a higher pervaporation performance of a composite membrane consisting of a selective layer of spin-coated PHEMA on a PHEMA-grafted PVDF substrate (S-PHEMA/PHEMA-g-PVDF). The composite membrane depth profile illustrated that an S-PHEMA layer spin-coated at a higher revolutions per minute (rpm) was thinner and denser than that at a lower rpm.

Biodegradable composition of poly(lactic acid) from renewable wood flour

Maleic anhydride-grafted poly(lactic acid) (PLA-g-MAH) was prepared by blending with wood flour (WF). The effect of MAH and WF inclusion on the mechanical and thermal properties of the composites was examined. PLA-g-MAH/WF had optimum tensile properties compared with PLA/WF. Scanning electron microscopic images indicated poor interfacial adhesion of the PLA/WF. It was enhanced after MAH was grafted onto PLA; the PLA-g-MAH/WF showed excellent compatible morphology. Results also revealed that the biodegradation of PLA and PLA-g-MAH was improved with increasing of WF content.

Solving the Charging Effect in Insulating Materials Probed by a Variable Monoenergy Slow Positron Beam

A variable monoenergy slow positron beam (VMSPB) operating at a high vacuum on insulating materials encounters a problem of significant surface charging effect with time. As a result, positronium formation is inhibited, and the positron annihilation radiation counting rate is reduced; these consequently distorted the experimental positron annihilation and results. To solve such problems, a technique of depositing an ultrathin layer of sputtering noble metals on insulators is developed. We report a successful method of sputtering a few atomic layers of platinum (∼1 nm) on a polyamide membrane to completely remove the charging effect for VMSPB applications in insulators.

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.

Effects of different metals on the synthesis and properties of waterborne polyurethane composites containing pyridyl units

This study used dicyclohexylmethane 4,4-diisocyanate, polybutylene adipate, polyether-1,3-diol, and 2,6-pyridinedimethanol to synthesize a novel water-based polyurethane (WPU) that contained pyridyl units. To enhance the thermal, mechanical, swelling, and antimicrobial properties of the WPU, various metals (silver nitrate, copper acetate, cobalt acetate, and zinc acetate) were incorporated to form WPU/metal composites. In addition, the study investigated the effects of the metal types on the WPU properties. Fourier transform infrared spectroscopy was used to confirm the synthesis of the WPU containing pyridine. Atomic force microscopy illustrated that the added metals increased the WPU surface roughness. The contact angle and degree of swelling tests demonstrated that the added metal reduced the WPU hydrophilicity, and with the addition of other metal types, the hydrophobicity increased considerably. Thermal gravimetric analysis indicated that the initial decomposition temperature of the highest WPU thermal stability was attributed to zinc. In addition, the results of differential scanning calorimetry and dynamic mechanical analysis showed that adding a small amount of metal increased the hard and soft segment glass transition temperatures. A universal strength tester validated that the WPU mechanical properties varied with the different metal additives and that the WPU strength increased. However, the WPU toughness and ductility decreased with the addition of metals; silver provided the highest mechanical strength. An antimicrobial test indicated that silver enhanced the antimicrobial property. The moisture permeability and waterproof property of the WPU coating was also analyzed.

One-step constructed ultrathin Janus polyamide nanofilms with opposite charges for highly efficient nanofiltration

Preparation of nanofiltration membranes (NFMs) with high rejection to both divalent cations and anions and simultaneous high water permeation is rather significant and highly desired. Herein, we engineered an ultrathin Janus polyamide (PA) separating layer with opposite charges in one step through the “self-regulation” process of low temperature interfacial polymerization (LTIP). The low temperature strategy plays a crucial role in optimizing the “self-regulation” process. It can reduce the transmission rate of aqueous monomers to the top reaction zone and thus the thickness of the reaction zone, resulting in an ultrathin Janus PA separating layer. Owing to the collaborative separation effect and reduced thickness of the Janus separating layer, our NFMs exhibit excellent comprehensive separation performance with high rejection to both divalent cations and anions and desirable water permeation, simultaneously, which exceeds the separation performance upper bound of state-of-the-art NFMs. Furthermore, these NFMs show outstanding anti-fouling performance owing to the uniform and smooth upper surface. The methodology reported here is easy to couple with current commercialized interfacial polymerization technology, making up-scaling feasible.