Development of lavender oil based polymer films for emerging technologies

Easton, Christopher (2009) Development of lavender oil based polymer films for emerging technologies. PhD thesis, James Cook University.

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The fabrication of novel and optimised materials, in addition to the development of techniques and procedures for characterisation of thin film samples continues to gain interest in the material science/engineering research area. These new polymers have the potential to provide improvement for existing technology, as well as avenues for new applications in fields including organic (flexible) electronics, optical and biomedical. The focus of this work is to develop new polymers for use in the identified applications from environmentally friendly resources. In addition to the technological benefits of this work, implementation of Australian resources in these fields would provide great benefit to local industry. This philosophy led to the choice of Lavandula angustifolia essential oil (LAEO) produced in Australia for the fabrication of the new polymers. This thesis studies investigates the fabrication of essential oil based polymer thin films from LAEO and some of its major individual components.

The resultant LAEO based polymer films have been characterised using a number of techniques and instruments, including spectroscopic ellipsometry, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, dielectric resonator techniques, atomic force microscope, scanning electron microscope, and contact angle. Using these characterisation tools, the properties of the resultant polymers were defined.

The LAEO based polymers were shown to be primarily hydrocarbon based, with some oxygen containing functional groups including ketones and hydroxyl groups. The presence of aromatics was also confirmed which are most likely formed during the polymerisation process. It was found that an increase in RF power resulted in a greater loss in the monomer functional groups and was assigned to an increase in energy input into the plasma system and an increase in substrate temperature.

Optical characterisation of the LAEO based polymers fabricated at various RF power levels confirmed that they are optically transparent and isotropic. Refractive index ranged from 1.530 to 1.543 at 500 nm for films fabricated using RF powers from 10 to 75 W. The optical band gap was found to decrease with increasing RF power, with 2.75 at 10 W and 2.34 at 75 W, and thus is within the range of band gap values defined for semiconductors.

Surface images obtained at the micro- and nano-meter scales demonstrated that the LAEO based polymers were uniform, smooth and pinhole free. The average roughness was found to be less than a nanometer.

Stability of the polymer while in contact with various solvents was examined using contact angle measurements. It was discovered that the polymer is very stable while in contact with water, with contact angle ranging from mildly hydrophilic (81.93º) at 10 W to mildly hydrophobic (91.95º) at 75 W. The surface tension components of the polymer were derived from the contact angle data. The LAEO based polymer was found to be monopolar in nature. Interfacial tension values were obtained for the polymer-solvent systems and the solubility characteristics of the polymer derived. These results specified that the polymer should resist solubilisation from the solvents explored.

Adhesion quality testing was performed on samples fabricated at various RF power levels and on common substrate materials. The quality was found to improve with increasing RF power, and was associated with an increase in the interfacial bonding.

LAEO based polymers exposed to ambient conditions were monitored for 1400 hours to provide information concerning the ageing mechanisms using spectroscopic ellipsometry and FTIR spectroscopy. The bulk of the ageing was found to occur within the first 100 hours after deposition, with the ageing mechanism following the typical oxidation path via the inclusion of additional hydroxyl for the higher power samples. At 10 W however, the mechanism was different, where no apparent uptake of oxygen occurred, and instead there was a significant loss of thickness.

Thermal degradation results demonstrated that the stability of the LAEO based polymer increased with RF power. Heating to 405ºC resulted in minimal residue for all samples. The major components of the LAEO monomer employed throughout this thesis were identified and polymers fabricated from these precursors. Overall it was found that the monomers with oxygen containing functional groups produced polymers with similar characteristics to that of the LAEO based polymer. The results indicated that polymers with similar characteristics to that of the LAEO based polymer could be fabricated from LAEO irrespective of the composition of the monomer.

Polymer thin films were fabricated from 1,8-cineole and the properties obtained using a number of techniques studied. This monomer can make up a significant portion of LAEO, however there was no detectable amount in the LAEO employed during this thesis. This monomer is also known to be a major component of eucalyptus oil.

A new technique for measuring the permittivity of low permittivity thin films at microwave frequencies was developed. This technique provided an accurate and nondestructive characterisation tool for these types of materials which was not previously possible.

From the characterisation data obtained, the suitability of the polymer in particular applications was discussed. Potential applications identified include employing these polymers in semiconductor applications, in the biomedical field as bio-reactive (LAEO based polymer) and non-bio-reactive (1,8-cineole) coatings, and as a sacrificial material in air gap fabrication.

Overall, during this thesis polymer thin films were successfully fabricated from LAEO and the major components and the properties of these polymers were determined. Additionally, a new technique for measuring the dielectric parameters of low permittivity thin films was defined. Potential applications for these polymers have been identified based on the characterisation data, as well as avenues for future work.

Item ID: 7904
Item Type: Thesis (PhD)
Keywords: thin film polymer, plasma polymerisation, organic semiconductors, ellipsometry, lavender oil based polymer films, lavender oil, semiconductor technology design, thin film fabrication
Date Deposited: 11 Jan 2010 06:17
FoR Codes: 09 ENGINEERING > 0910 Manufacturing Engineering > 091009 Microtechnology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970110 Expanding Knowledge in Technology @ 100%
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