The continuous manufacture of dispersant coated bioresorbable nanoparticles

Walton, Kirsty E. (2018) The continuous manufacture of dispersant coated bioresorbable nanoparticles. PhD thesis, University of Nottingham.

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This thesis investigates the continuous synthesis and coating of hydroxyapatite nanoparticles (HA NP’s). A range of dispersant molecules were produced and subsequently used in this continuous coating process. Starting with small aliphatic hydrocarbon chains attached to various functional groups a basic understanding of the interactions occurring between the dispersant molecule, the hydroxyapatite surface and a solvent medium was built. It became clear that the length of the hydrocarbon chain, the nature of the functional group and the morphology of the dispersant all had a role to play in the effectiveness and extent of the coating. Using this fundamental understanding the work progressed into the realm of polymeric dispersants. The biodegradable and bioresorbable polymer, polylactic acid (PLA) was utilised in the coating process with the aim of producing HA NP’s that could be dispersed within a polymer matrix. These low molecular weight (Mw) polymers were based on similar chain size and functional groups chemistry. Similar linear morphologies were investigated along with a new six armed, branched morphology. It was concluded that molecular weight of the polymer (chain length), the functional head group (initiator) and morphology of the polymer were all responsible for the dispersant to successfully coat the HA NP’s. However, results indicated that different surface interactions were occurring between the polymeric dispersant chain and HA than those occurring between the hydrocarbon chain and HA. The conclusion that had been drawn from our hydrocarbon coated HA NP’s was that the interaction between dispersant and surface primarily resulted from the functional group. The aliphatic carbon chain would not form any significant surface bonds. This was not the same conclusion drawn from the results of our polymeric dispersants, which appeared to interact favourably with the highly charged nanoparticle surface.

A wide range of analytical techniques have been employed in this thesis to fully understand the surface chemistry occurring between dispersant and nanoparticle surface. Gel-permeation chromatography (GPC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy have been used to explore the chemistry and morphology of the dispersants. Understanding the interactions between the hydroxyapatite surface and the dispersant molecule proved more challenging. Multiple electron microscopy techniques, including scanning electron microscopy (SEM), tunnelling electron microscopy (TEM), electron energy loss (EEL) spectroscopy along with TGA and FTIR spectroscopy provided an insight into the dispersant-surface interactions. Elemental analysis, such as X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) also provided support to the theories developed throughout the project. It was vital that such a wide range of analytical techniques were explored as no one technique could provide the full picture of the surface chemistry.

Whilst the many conventional analytical approaches directed our focus to a combination of functional groups and chain lengths, the exact nature of the bonds between dispersant and nanoparticle surface remained elusive. Often NMR spectroscopy, being one of the most powerful tools in understanding chemical bonds, would be able to provide such information. Due to the physical nature of our final nanocomposite material, solution state NMR spectroscopic analysis was not possible leading our investigation into the realm of solid-state NMR spectroscopy. With the help of the Nottingham University’s solid-state NMR research group 1H-31P correlation experiments were used to investigate the interactions between the dispersant molecules and the surface of HA NP’s. The spectra revealed that hydrocarbon based dispersant primarily interacted with the surface via their functional head group. PLA based dispersant spectra were dominated by resonances arising from polymer chain – hydroxyapatite surface interactions. Dynamic nuclear polarization (DNP) solid-state NMR selectively enhanced the surface interactions and supported the conclusions drawn from the standard solid-state NMR correlation spectroscopy. Solid-state NMR spectroscopy was able to provide the final crucial piece of evidence that supported the conclusions drawn from Chapter’s 2 and 3.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Irvine, Derek
Lester, Ed
Howdle, Steven M.
Keywords: Hydroxyapatite; Nanoparticles; Dispersing agents; Coatings
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 49840
Depositing User: Walton, Kirsty
Date Deposited: 13 Jul 2018 04:40
Last Modified: 08 May 2020 08:30

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