Surface properties of electrospun polymer nanofibres
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Fibrous materials are used in a variety of applications due to their relatively high
surface area to volume ratio as well as anisotropic behaviour. Electrospinning is a
popular fabrication technique which produces polymer nanofibres with a
potentially high molecular orientation. The surface of polymer fibres plays a
significant role in many applications thus measurement of their surface properties
is essential but challenging due to their relatively small size. In this thesis,
ultrafine nanofibres have been produced by electrospinning with their nanofibre
morphology controlled by varying different processing parameters. Atomic force
microscopy (AFM) adhesion contact mechanics and individual nanofibre wetting
measurements have been conducted to explore surface properties of the produced
electrospun polymer fibres. Results using traditional Owens-Wendt plots applied
to our nanomaterials show electrospun nanofibres have a higher dispersive surface
free energy compared to bulk polymer film but a lower polar contribution, giving
a total surface free energy in excess of bulk equivalents. A novel proposed model
indicates that this nanofibre dispersive surface free energy is intimately linked to
density of the polymer and ultimately the molecular spacing or orientation for the
polymer chains. Comparisons are made with bulk polymer films to show that a
high degree of molecular orientation is present at least at the surface of the
polymer nanofibre. Structure investigations on electrospun fibres of polyvinyl
alcohol using FTIR and XPS surface techniques explore how an increase in
hydrogen bonds formed within nanofibres rather than on the fibre surface enhance
this dispersive contribution but lowers the polar contribution. The wetting
behaviour of electrospun fibre is extended to assemblies at length scales above
individual fibres to highlight how superhydrophobic surfaces can be produced
from nanofibre networks with defined spacings and geometries. This
superhydrophobicity was adequately described by a Cassie-Baxter model
modified to account for the fibrous geometry.
Authors
Li, ShuangwuCollections
- Theses [3822]