The electrospinning technique transforms a polymer solution of sufficient concentration from a sub-millimetre sized droplet to a fibre ranging in diameter from tens of micrometers to tens of nanometres by application of a sufficiently strong electric field. A polymer jet is extruded from the droplet and a solid fibre is deposited onto a grounded collector. During this transition a large scale transformation occurs and the solvent is rapidly removed from the polymer jet. The purpose in this investigation is to develop a model of how the polymer chain conformation is altered from the solution state to that of the fibre by the electrospinning process using the technique of small angle neutron scattering (SANS). Using SANS in conjunction with isotopically labelled samples the polymer chain conformation in high dielectric constant solvents was measured at the high concentrations, associated with electrospinning. It was determined that for the concentrations used in electrospinning in this work, the solutions were all in the semi-dilute state, meaning that the polymer chain was in a swollen conformation and its dimensions were greater than those in the bulk state. The chain conformation in the polymer fibres was also measured with the aid of SANS and was determined to exhibit chain dimensions comparable to that measured in the solution. The level of extension inherent to the electrospinning process was measured by collection of aligned fibres. It was determined that the chains extend ~5% parallel to the fibre axis. A relatively small extension compared to the large macroscopic transformation of the fibre. The level of extension was further increased to ~20% through mechanical deformation by use of a rotating collector. The polymers relaxation rate, the solvent evaporation rate and any formation of a polymer skin play a significant role in determining the level of molecular anisotropy in the fibres.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:577778 |
| Date | January 2011 |
| Creators | Mohan, Saeed |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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