Showing papers by "Greg G. Qiao published in 2013"

Highly permeable membrane materials for CO2 capture

Abstract: The release of large quantities of CO2 into the atmosphere has been linked to global warming and climate anomalies. Membrane processes offer a potentially viable energy-saving alternative for CO2 capture in comparison with conventional technologies such as amine absorption. However, gas separation membranes that are currently available have insufficiently high permeance (flux) for large scale applications such as the treatment of high volume flue gas with low concentration of CO2. Here we demonstrate a class of thin film composite (TFC) membranes, consisting of a high molecular weight amorphous poly(ethylene oxide)/poly(ether-block-amide) (HMA-PEO/Pebax® 2533) selective layer and a highly permeable polydimethylsiloxane (PDMS) intermediate layer which was pre-coated onto a polyacrylonitrile (PAN) microporous substrate. In contrast to the performance of conventional materials, the selective layer of TFC membranes shows super-permeable characteristics and outstanding CO2 separation performance. This unprecedented result arises from the introduction of HMA-PEOs into the Pebax® 2533 matrix, leading to high CO2 permeability and flux. These results provide an encouraging direction to further develop TFC membranes for efficient CO2 capture processes.

Enhancement of radiation effects by bismuth oxide nanoparticles for kilovoltage x-ray beams: A dosimetric study using a novel multi-compartment 3D radiochromic dosimeter

Abstract: The aim of this study is to present the first experimental validation and quantification of the dose enhancement capability of bismuth oxide nanoparticles (Bi2O3-Nps). A recently introduced multi-compartment 3D radiochromic dosimeter for measuring radiation dose enhancement produced from the interaction of X-rays with metal nanoparticles was employed to investigate the 3D spatial distribution of ionizing radiation dose deposition. Dose-enhancement factor for the dosimeters doped with Bi2O3-NPs was ~1.9 for both spectrophotometry and optical CT analyses. Our results suggest that bismuth-based nanomaterials are efficient dose enhancing agents and have great potential for application in clinical radiotherapy.

A novel one-pot approach towards dynamically cross-linked hydrogels

Abstract: Herein, we report the synthesis of sliding-ring (SR) hydrogel networks in a one-pot click-mediated approach using α,ω-dialkyne poly(ethylene glycol) (PEG) and azido-functionalised cyclodextrin, which acts as both sliding cross-link and end-capping agent. This novel approach resulted in polymeric networks that possess a combination of both SR and covalent (CV) cross-link points. The extent of inclusion complexation and the ratio of SR to CV cross-links in the hydrogels was found to be dependent on both the concentration of the precursors and the curing temperature. Based upon model studies where rotaxanes were synthesised from the same precursors, it was observed that an increase in the precursor concentration led to an increase in click efficiency and inclusion ratio, which in turn affects the overall hydrogel rigidity and elasticity. Hydrogels synthesised at higher curing temperatures led to more homogeneous networks that were significantly tougher as a result of the overall increase in cross-linking density and the extent of CV cross-links. We therefore present a facile one-pot method for the synthesis of SR networks with tunable physicochemical properties. Additionally, the resultant hydrogel networks are potentially capable of supporting post-modification with various (bio)molecules or therapeutics utilizing the remaining azide groups on the cyclodextrin cross-links. Preliminary cytotoxicity studies revealed that the hydrogels did not impede cell growth and demonstrate negligible toxicity. Thus, these networks may have potential for soft-tissue engineering or biomedical applications, including sustained release and drug-delivery systems.

Super)hydrophobic and Multilayered Amphiphilic Films Prepared by Continuous Assembly of Polymers

Abstract: The continuous assembly of polymers (CAP) is used to fabricate tailored nanocoatings on a wide variety of substrates. Ring-opening metathesis polymerization (ROMP) is used to mediate the CAP process (CAPROMP) to assemble specifically designed macromolecules into nanoengineered crosslinked films. Different films composed of single or multiple macromolecules are used to tune the surface wetting characteristics on various planar substrates, including porous substrates such as filter paper and cotton, and non-porous subtrates such as aluminium foil and glass. By judicious selection of the macromolecules, these substrates, which are hydrophilic in nature, can be rendered (super)hydrophobic. The robustness of the ROMP catalysts and the reinitiation ability of the CAPROMP approach allow the production of layered multicomponent amphiphilic films with on-demand switchable wettability. Such functional nanocoatings can be potentially applied as self-cleaning surfaces, as waterproof woven fabrics, and for the next generation of microelectronic devices. The continuous assembly of polymers (CAP) is utilized to fabricate advanced functional nanocoatings with tunable film compositions on various substrates. The versatility of CAP is demonstrated by the formation of (super)hydrophobic coatings on hydrophilic substrates including paper, cotton, aluminium foil, and glass. Moreover, by simple alternate dipping in hydrophilic and hydrophobic macro-crosslinker solutions, novel stratified amphiphilic films can be assembled via CAP. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ring-opening metathesis polymerization with the second generation Hoveyda-Grubbs catalyst: an efficient approach toward high-purity functionalized macrocyclic oligo(cyclooctene)s.

Abstract: Herein, we present a facile and general strategy to prepare functionalized macrocyclic oligo(cyclooctene)s (cOCOEs) in high purity and high yield by exploiting the ring-opening metathesis polymerization (ROMP) intramolecular backbiting process with the commercially available second generation Hoveyda–Grubbs (HG2) catalyst. In the first instance, ROMP of 5-acetyloxycyclooct-1-ene (ACOE) followed by efficient quenching and removal of the catalyst using an isocyanide derivative afforded macrocyclic oligo(5-acetyloxycyclooct-1-ene) (cOACOE) in high yield (95%), with a weight-average molecular weight (Mw) of 1.6 kDa and polydispersity index (PDI) of 1.6, as determined by gel permeation chromatography (GPC). The structure and purity of the macrocycles were confirmed by NMR spectroscopy and elemental analysis, which indicated the complete absence of end-groups. This was further supported by GPC-matrix assisted laser desorption ionization time-of-flight mass spectroscopy (GPC-MALDI ToF MS), which revealed the exc...

Molecular Mechanism of Stabilization of Thin Films for Improved Water Evaporation Protection

Abstract: All-atom molecular dynamics simulations and experimental characterization have been used to examine the structure and dynamics of novel evaporation-suppressing films where the addition of a water-soluble polymer to an ethylene glycol monooctadecyl ether monolayer leads to improved water evaporation resistance. Simulations and Langmuir trough experiments demonstrate the surface activity of poly(vinyl pyrrolidone) (PVP). Subsequent MD simulations performed on the thin films supported by the PVP sublayer show that, at low surface pressures, the polymer tends to concentrate at the film/water interface. The simulated atomic concentration profiles, hydrogen bonding patterns, and mobility analyses of the water-polymer-monolayer interfaces reveal that the presence of PVP increases the atomic density near the monolayer film, improves the film stability, and reduces the mobility of interfacial waters. These observations explain the molecular basis of the improved efficacy of these monolayer/polymer systems for evaporation protection of water and can be used to guide future development of organic thin films for other applications.

Assembly of Nanostructured Films with Hydrophobic Subcompartments via Continuous Assembly of Polymers

Abstract: The generation of nanoscale polymer films using complex, hierarchically structured (bio)macromolecular architectures has important implications in the field of materials science. This study details the surface-confined covalent cross-linking of micellar macrocross-linkers derived from the amphiphilic diblock copolymer, polystyrene-b-poly(N-(2-hydroxypropyl)methacrylamide), via atom transfer radical polymerization (ATRP)-mediated continuous assembly of polymers (CAPATRP), to generate compartmentalized thin films with unique surface morphologies. Using initiator-functionalized silicon wafers, the micellar films were found to be thicker in comparison to thin films prepared from linear macrocross-linkers derived from poly(N-(2-hydroxypropyl)methacrylamide) (15.2 vs 10.2 nm). Unlike the smooth and flat surface morphologies observed for films prepared from the linear macrocross-linker, the micellar films possessed distinctive pitted morphologies that became more pronounced after annealing. Furthermore, the hydr...

Assembly of Free-Standing Polypeptide Films via the Synergistic Combination of Hyperbranched Macroinitiators, the Grafting-From Approach, and Cross-Chain Termination

Abstract: Cross-linked polypeptide-based films are fabricated via a novel and robust method employing surface-initiated ring opening polymerization of α-amino acid N-carboxyanhydrides (NCA-ROP). The judicious combination of amine-based hyperbranched macroinitiators and benzyl ester-protected NCA derivatives promotes network formation by cross-chain terminations, which allows the formation of stable cross-linked peptide-based capsules in a one-pot system.

Molecular interactions behind the synergistic effect in mixed monolayers of 1-octadecanol and ethylene glycol monooctadecyl ether.

Abstract: Mixed monolayers of 1-octadecanol (C18OH) and ethylene glycol monooctadecyl ether (C18E1) were studied to assess their evaporation suppressing performance. An unexpected increase in performance and stability was found around the 0.5:0.5 bicomponent mixture and has been ascribed to a synergistic effect of the monolayers. Molecular dynamics simulations have attributed this to an additional hydrogen bonding interaction between the monolayer and water, due to the exposed ether oxygen of C18E1 in the mixed system compared to the same ether oxygen in the pure C18E1 system. This interaction is maximized around the 0.5:0.5 ratio due to the particular interfacial geometry associated with this mixture.

Formation of Dynamic Duolayer Systems at the Air/Water Interface by using Non-ionic Hydrophilic Polymers

Abstract: The inclusion of a water-soluble polymer, poly(vinyl pyrrolidone) (PVP), into a surface active film composition before application to the water surface leads to the formation of a dynamic duolayer; a novel surface film system. This duolayer shows improved surface viscosity over the monolayer compound alone, while the addition of polymer maintains other film properties such as evaporation control and equilibrium spreading pressure. Brewster Angle Microscopy shows that the duolayer film undergoes a different formation mechanism upon film compression, and the resultant surface pressure/area isotherm is different at lower surface pressures indicating the PVP is present on the water surface at these pressures and squeezed out to the water subphase at higher pressures. The addition of water-soluble polymers to form a dynamic duolayer provides a unique way to produce defect-free and tightly packed films while polymer is associated with the film. This finding provides new knowledge for the design of surface films with improved properties with potential applications in many areas.