| Summary: | <p>This thesis develops our understanding of the experimental variables, and viability, for the film production of primarily hexagonal boron nitride (hBN). This is initially achieved by a successful investigation of the dispersibility and deposition of hBN analogous carbon nanotubes (CNT) to create films by the novel combination of CNT reduction and electrophoretic deposition (EPD). This process is then successfully, and for the first time, applied to boron nitride nanotubes (BNNT) and 2D boron nitride platelets (BNP). The reduced dispersion for EPD process bypasses the traditional need to oxidise the starting nanomaterial which can damage the materials’ nanostructure. However, any comparative study for the oxidation of hBN materials is problematic as these processes are an underdeveloped field of research. The latter sections of this thesis therefore show that traditional acid oxidation methods used for carbon nanomaterials are ineffective at functionalising, dispersing and depositing the more inert hBN materials.</p>
<p>The novel and improved method for neat CNT film production is first developed by the combination of two established techniques: the electrochemical reduction and suspension of single walled carbon nanotubes (SWCNT) by sodium naphthalide (NaNap), and the charged particle coagulation of EPD. This ‘reduced dispersion for EPD method’ creates SWCNT films of controllable thicknesses (0-14 µm), in short amounts of time (5-120 s) and requires low field strengths (1-5 V cm-1) to do so. The final nanomaterial products are conductive, mechanically strong, and thermally stable SWCNT films which crucially retain the nanostructure of their initial starting material without the need for additional chemical modification, additives or binders. Free-standing examples of these materials are compared to samples made using the traditional oxidation-based methodology and are found to be mechanically weaker (8.4 vs 14.9 MPa Youngs modulus) and poorer electrical conductors (229 S cm-1 vs 694 ±18 S cm-1). This is due to the thicker films containing void spaces caused by the removal of sodium crystals during the post-EPD washing of the samples and thereby increasing the porosity and reducing the density of the material.</p>
<p>This thesis then shows the first reductive dispersion and first EPD of BNNT. It is found that the charge ratio on BNNT is significantly lower (<41BN:1Na) than for CNT (5C:1Na) and subsequently EPD deposition rates are slower (2.03 µg cm-2 min-1). It is hypothesised that this causes the resultant BNNT films to be thicker than CNT (up to 35 µm). The nanotubes within films are proved to have near identical nanostructures to their starting materials showing that the dispersion and EPD processes were none-damaging. However, the similar film density of these materials to CNT equivalents (0.31 g cm-3) and poor mechanical performance imply similar issues with film porosity.</p>
<p>Finally, various solution-based acid etching techniques and methodologies described across literature for carbon nanomaterials are applied to BNP which are shown to be inert to these conditions. Dispersion of these materials is still achieved by bath sonication which is shown to the most effective benchtop method for doing so (concentrations up to 0.232 mg mL-1). EPD of the resulting suspensions was slow and produced negligible hBN films leading to the conclusion that this is not an efficient method of film production, especially when compared to the reduced dispersion for EPD method developed previously in this work.</p>
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