AbstractNano and micro-fibres can exhibit properties which enhance their performance at certain tasks due to their high surface-to-volume ratio, porosity, and tailorable characteristics. Structuring these fibres into a gradient form, in which one or more of their properties gradually changes over the membrane superstructure, can enhance their performance at certain tasks and grant them the ability to perform new functions. Electrospinning is the most commonly used fabrication method for these materials, but this method has limitations in the rate of material fabrication, the forms it can produce, and the surfaces it can spin fibres on. The aim of this thesis is to investigate the application of an alternative fibre fabrication technique to overcome these limitations and produce new forms of gradient fibre membranes which exhibit novel functions. This is developed by a literature review examining alternative fibre fabrication techniques, the use of fillers to enhance the properties of the membranes, and the form and function of existing functional gradient nanofibres (FGNFs). Solution blow spinning (SBS), an emerging nanofibre fabrication technique which uses blown air to fabricate fibre membranes on a wide range of surfaces, was chosen to fabricate a novel FGNF. Two material pairs were chosen as FGNF candidates. The first pair, poly(vinylidene fluoride) (PVDF)/ graphene oxide (GO), was chosen due to its high performance at multiple functions, in particular its piezoelectric energy harvesting capability. The second pair, poly(methyl methacrylate) (PMMA)/PVDF, was chosen due to the miscibility of the two polymers and their tailorable wettability. To fabricate high performance FGNFs, three separate experiments were performed. The first experiment was designed to reduce the incidence of beads which are pervasive in SBS PVDF membranes, which detrimentally effect the mechanical integrity and morphological homogeneity of the material. This was achieved by adding controlled heating elements to the SBS apparatus to prevent the formation of PVDF microgels, resulting in bead-free SBS PVDF for the first time. In the second experiment a PVDF membrane which contained a GO gradient was fabricated and characterized, resulting in a membrane with a gradient in electroactive crystalline phase. Though the membranes did not exhibit any significant piezoelectric output when spun either via conventional SBS or with an assisting electrostatic field, the material produced is an attractive candidate for wastewater treatment, irradiation protection and membrane antifouling applications. The third experiment investigated the production of a PMMA/PVDF membrane with a gradient in oil and water permeation rates to fractionate a mixture of oil and water. This was achieved by spinning PMMA/PVDF membranes of gradually increasing thickness over an open-sided container, resulting in a FGNF membrane which fractionated oil and water. The ability to fabricate a functional gradient nanofibre membrane on any surface which fibres will form on via SBS presents the potential to fabricate large-scale FGNFs on almost any surface.
|Date of Award
|31 Dec 2020
|Nicola Tirelli (Supervisor) & Jonny Blaker (Supervisor)
- Solution blow spinning