Investigation into the effects of ionising radiation on plasma polymer monoterpene alcohols for applications in organic electronics

Grant, Daniel Shane (2017) Investigation into the effects of ionising radiation on plasma polymer monoterpene alcohols for applications in organic electronics. PhD thesis, James Cook University.

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Plasma polymers are coming to occupy a niche position in the development of functionalised thin films for use in electronic, biomedical, and optical devices. In particular, plasma polymers synthesised from natural organic precursors, such as essential oils, have demonstrated promising properties relating to electronic charge transport/insulation, biocompatibility, and protective device encapsulation. Several of these environmentally friendly precursors, including terpinen-4-ol, are derived from resources native to Australia and their commercial uptake in plasma polymer-enabled technologies holds economic benefits for Australian industry.

This commercial uptake can be advanced through several initiatives. First, the economics of the plasma polymer synthesis process can be improved through better understanding of the relationship between precursor, plasma environment, and polymer properties. Second, efforts can be made to demonstrate the retention of electronically and biomedically relevant properties following exposure to a standardised sterilisation process, such as gamma irradiation. Finally, the range of suitable applications for plasma polymers can be expanded by developing new techniques (such as radiation processing) for tailoring and enhancing their chemical and physical properties.

Resultantly, this thesis focussed on the cold plasma synthesis of polyterpenol thin films from the natural terpinen-4-ol precursor, and the subsequent exposure of these films to a variety of ionising radiation sources and species.

The synthesis process involved the introduction of terpinen-4-ol monomer units (a monocyclic terpene alcohol extracted from the distillation of Melaleuca alternifolia oil) into a radio frequency glow discharge. Subsequent fragmentation and recombination/deposition of species within the plasma led to the formation of thin, flexible, and morphologically uniform polyterpenol films. Following synthesis, the polyterpenol films were exposed to ionising radiation in the form of swift heavy ions from an ion beam, gamma rays from a cobalt-60 source, and high-temperature species generated by a dense plasma focus device.

The energy, type, and relative abundance of plasma species was explored using residual gas analysis and positive ion mode quadrupole mass spectrometry. Properties of the irradiated polyterpenol thin films were examined using crystal quartz microbalance analysis, spectroscopic ellipsometry, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron spectroscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray reflectometry, and two-probe current-voltage and capacitive characterisation.

Specific findings from this thesis include:

• Determination that the plasma environments of terpinen-4-ol and Melaleuca alternifolia oil (from which terpinen-4-ol is distilled) show increasing commonalities in plasma species as the applied power is increased. This finding indicates that the less processed Melaleuca alternifolia oil may be used as a cost-effective substitute for terpinen-4-ol in applications that are reliant primarily on the mechanical and physical properties of the resultant plasma polymer. Conversely, priority should be given to the use of terpinen-4-ol in a low power plasma environment for the synthesis of films that are required to demonstrate traits that are strongly dependent on chemical functionalities (e.g., antibacterial coatings, or coatings to support endothelialisation).

• Determination that high energy (~50 MeV) iodine ion (I¹⁰⁺) irradiation at low fluence (≤1×10¹² ions/cm²) can be employed to generate polyterpenol thin films with controlled surface pore density. This opens up the possibility of using porous polyterpenol thin films as nano- or micro-porous filtration membranes, or as loading and controlled dispersal platforms for pharmaceutical products.

• Determination that high energy (~55 MeV) iodine ion (I⁹⁺) irradiation at high fluence (≥1×10¹³ ions/cm²) can be employed to convert polyterpenol thin films into graphitic-polymer nanocomposite films, whilst still retaining some degree of polymer chemical functionality. This opens up the possibility of using high fluence ion treatment of polyterpenol to synthesise layers for use in supercapacitors, organic electronics, membranes, and biological assay.

• Determination that the physical and chemical characteristics of polyterpenol exhibit stability following gamma irradiation at doses up to four times in excess of the 25 kGy dose commonly employed to sterilise materials for biomedical applications. The antibacterial properties of polyterpenol (specifically with respect to the pseudomonas aeruginosa pathogen) are strongly dependent upon the surface morphology and chemical functionalities of the film. The retention of these characteristics following gamma irradiation at doses well in excess of 25 kGy suggests that polyterpenol antibacterial coatings (for devices such as in-dwelling implants) may be valid targets for gamma sterilisation processes.

• Determination that exposure to extremely high temperature transient irradiation from a dense plasma focus device can induce inelastic deformation of plasma polymer films. Plasma polymers exhibit a high degree of crosslinking, and as such behave in a fashion similar to that of thermosetting polymers when heated (i.e., they char and decompose). The high heating slope and rapid cooldown time associated with dense plasma focus treatment permits chain mobility and plastic behaviour to occur before thermal degradation is expressed. This has implications for reshaping plasma polymers, and enables the formation of novel topographical features (such as hollow bubble-like cavities).

In summary this thesis has enhanced the understanding of plasma chemistry relevant to naturally occurring terpene precursors, and expanded the suite of post-synthesis techniques that can be applied to tailor the properties of plasma polymerised polyterpenol thin films. Applications relating to these developments have been identified, and future avenues for investigation have been proposed.

Item ID: 53104
Item Type: Thesis (PhD)
Keywords: AFM, composites, dense plasma focus, ellipsometry, gamma radiation, inelastic deformation, ion energy distribution, ion irradiation, ionising radiation, mass spectrometry, Melaleuca alternifolia, organic electronics, plasma polymer, plasma polymerisation, polymer degradation, polymer irradiation, polyterpenol, radiation processing, Raman spectroscopy, sterilisation, swift heavy ions, terpinen-4-ol, thermal degradation, thin films, XRR
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For this thesis, Daniel Grant received the Dean's Award for Excellence 2018.

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 4: Grant, Daniel S., Bazaka, Kateryna, Siegele, Rainer, Holt, Stephen A., and Jacob, Mohan (2015) Ion irradiation as a tool for modifying the surface and optical properties of plasma polymerised thin films. Nuclear Instruments & Methods in Physics Research Section B, 360. pp. 54-59.

Chapter 5: Grant, Daniel S., Rawat, Rajdeep S., Bazaka, Kateryna, and Jacob, Mohan V. (2017) Inelastic deformation of plasma polymerised thin films facilitated by transient dense plasma focus irradiation. Materials Research Express, 4 (9). pp. 1-4.

Date Deposited: 11 Apr 2018 04:43
FoR Codes: 09 ENGINEERING > 0912 Materials Engineering > 091209 Polymers and Plastics @ 100%
SEO Codes: 86 MANUFACTURING > 8698 Environmentally Sustainable Manufacturing > 869899 Environmentally Sustainable Manufacturing not elsewhere classified @ 50%
85 ENERGY > 8598 Environmentally Sustainable Energy Activities > 859899 Environmentally Sustainable Energy Activities not elsewhere classified @ 50%
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