Wendy Tian

Effects of MWNT nanofillers on structures and properties of PVA electrospun nanofibres

In this study, we have electrospun poly(vinyl alcohol)(PVA) nanofibres and PVA composite nanofibres containing multi-wall carbon nanotubes (MWNTs) (4.5 wt%), and examined the effect of the carbon nanotubes and the PVA morphology change induced by post-spinning treatments on the tensile properties, surface hydrophilicity and thermal stability of the nanofibres. Through differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD) characterizations, we have observed that the presence of the carbon nanotubes nucleated crystallization of PVA in the MWNTs/PVA composite nanofibres, and hence considerably improved the fibre tensile strength. Also, the presence of carbon nanotubes in PVA reduced the fibre diameter and the surface hydrophilicity of the nanofibre mat. The MWNTs/PVA composite nanofibres and the neat PVA nanofibres responded differently to post-spinning treatments, such as soaking in methanol and crosslinking with glutaric dialdehyde, with the purpose of increasing PVA crystallinity and establishing a crosslinked PVA network, respectively. The presence of carbon nanotubes reduced the PVA crystallization rate during the methanol treatment, but prevented the decrease of crystallinity induced by the crosslinking reaction. In comparison with the crosslinking reaction, the methanol treatment resulted in better improvement in the fibre tensile strength and less reduction in the tensile strain. In addition, the presence of carbon nanotubes reduced the onset decomposition temperature of the composite nanofibres, but stabilized the thermal degradation for the post-spinning treated nanofibres. The MWNTs/PVA composite nanofibres treated by both methanol and crosslinking reaction gave the largest improvement in the fibre tensile strength, water contact angle and thermal stability.

Polysaccharides as protectants for paper-based analytical devices with antibody

Paper with immobilized protein can provide a low-cost platform for diagnostics, but evidence is emerging that the instability of protein on paper during shipping and storage severely limits its commercial development. Of these, paper-immobilized antibody, though widely used, is in urgent need of improvement in the shelf life. Herein we provided a detailed investigation of a simple and versatile approach for achieving stable antibody on paper to improve bioassay performance. Anti-Blood Group A IgM was chosen as the model antibody and its activity was tested via agglutination reactions. Representative polysaccharides (i.e., chitosan, sodium alginate and dextran) were used as protectants and their ability to stabilize antibody under heat and desiccation stresses was investigated. It was found that the presence of dextran with high concentration markedly stabilized paper-immobilized IgM for at least 120 days. Our results indicate that dextran with good film-forming ability could be a protectant for paper-immobilized antibody.

Synthesis and characterisation of new sulphur-containing epoxy networks

The position of sulphur within a cured epoxy amine network and its impact upon the thermal, mechanical, chemical and physical properties has been investigated in this study. Sulphur-containing epoxy resins, diglycidyl thioether of bisphenol A (DGTEBA) and diglycidyl ether of dithio diphenyl (DGTED) have been synthesised, cured and characterised and then compared with the benchmark epoxy resin, diglycidyl ether of bisphenol A (DGEBA). DGTEBA has two sulphur atoms located terminally to the epoxide groups, whilst DGTED has a sulphur atom located centrally between two phenyl groups. Evaluation of the properties and cure mechanism using 4,4′-diamino diphenyl sulphone (4,4′-DDS) as the hardener showed that when the sulphur was terminally located, the glass transition temperature, cure conversion, thermal stability, yield strain and stress decrease substantially, whilst the rate of cure and methyl ethyl ketone (MEK) ingress was comparatively higher. Near-infrared spectroscopy revealed that a competing hydrogen abstraction reaction mechanism deactivated the epoxide ring to nucleophilic attack to produce a heterogeneous network and poorer properties. In contrast, the properties and network structure of the DGTED-cured network, which had sulphur placed centrally between the diphenyl groups were similar to DGEBA except that MEK fluid ingress was reduced. The DGTEBA epoxy was also cured with other amines of varying reactivity to reveal that the hydrogen abstraction mechanism was dependent upon the reactivity of the hardener. Less reactive hardeners were dominated by the hydrogen abstraction mechanism, whilst the more reactive amines displayed a step-growth mechanism more typically associated with epoxy amine cure.