Fabrication and characterization of plasma polymer thin films from monoterpene alcohols for applications in organic electronics and biotechnology

Bazaka, Kateryna (2011) Fabrication and characterization of plasma polymer thin films from monoterpene alcohols for applications in organic electronics and biotechnology. PhD thesis, James Cook University.

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After more than twenty years of basic and applied research, the use of nanotechnology in the design and manufacture of nanoscale materials is rapidly increasing, particularly in commercial applications that span from electronics across renewable energy areas, and biomedical devices. Novel polymers are attracting significant attention for they promise to provide a low−cost high−performance alternative to existing materials. Furthermore, these polymers have the potential to overcome limitations imposed by currently available materials thus enabling the development of new technologies and applications that are currently beyond our reach. This work focuses on the development of a range of new low−cost environmentally−friendly polymer materials for applications in areas of organic (flexible) electronics, optics, and biomaterials. The choice of the monomer reflects the environmentally−conscious focus of this project. Terpinen−4−ol is a major constituent of Australian grown Melaleuca alternifolia (tea tree) oil, attributed with the oil's antimicrobial and anti−inflammatory properties.

Plasma polymerisation was chosen as a deposition technique for it requires minimal use of harmful chemicals and produces no hazardous by−products. Polymer thin films were fabricated under varied process conditions to attain materials with distinct physico−chemical, optoelectrical, biological and degradation characteristics. The resultant materials, named polyterpenol, were extensively characterised using a number of well−accepted and novel techniques, and their fundamental properties were defined. Polyterpenol films were demonstrated to be hydrocarbon rich, with variable content of oxygen moieties, primarily in the form of hydroxyl and carboxyl functionalities. The level of preservation of original monomer functionality was shown to be strongly dependent on the deposition energy, with higher applied power increasing the molecular fragmentation and substrate temperature. Polyterpenol water contact angle contact angle increased from 62.7° for the 10 W samples to 76.3° for the films deposited at 100 W. Polymers were determined to resist solubilisation by water, due to the extensive intermolecular and intramolecular hydrogen bonds present, and other solvents commonly employed in electronics and biomedical processing.

Independent of deposition power, the surface topography of the polymers was shown to be smooth (Rq <0.5 nm), uniform and defect free. Hardness of polyterpenol coatings increased from 0.33 GPa for 10 W to 0.51 GPa for 100 W (at 500 μN load). Coatings deposited at higher input RF powers showed less mechanical deformation during nanoscratch testing, with no considerable damage, cracking or delamination observed. Independent of the substrate, the quality of film adhesion improved with RF power, suggesting these coatings are likely to be more stable and less susceptible to wear. Independent of fabrication conditions, polyterpenol thin films were optically transparent, with refractive index approximating that of glass. Refractive index increased slightly with deposition power, from 1.54 (10 W) to 1.56 (100 W) at 500 nm. The optical band gap values declined with increasing power, from 2.95 eV to 2.64 eV, placing the material within the range for semiconductors. Introduction of iodine impurity reduced the band gap of polyterpenol, from 2.8 eV to 1.64 eV, by extending the density of states more into the visible region of the electromagnetic spectrum. Doping decreased the transparency and increased the refractive index from 1.54 to 1.70 (at 500 nm).

At optical frequencies, the real part of permittivity (k) was determined to be between 2.34 and 2.65, indicating a potential low-k material. These permittivity values were confirmed at microwave frequencies, where permittivity increased with input RF energy – from 2.32 to 2.53 (at 10 GHz ) and from 2.65 to 2.83 (at 20 GHz). At low frequencies, the dielectric constant was determined from current−voltage characteristics of Al−polyterpenol−Al devices. At frequencies below 100 kHz, the dielectric constant varied with RF power, from 3.86 to 4.42 at 1 kHz. For all samples, the resistivity was in order of 10⁸−10⁹ _m (at 6 V), confirming the insulating nature of polyterpenol material. In situ iodine doping was demonstrated to increase the conductivity of polyterpenol, from 5.05 × 10⁻⁸ S/cm to 1.20 × 10⁻⁶ S/cm (at 20 V).

Exposed to ambient conditions over extended period of time, polyterpenol thin films were demonstrated to be optically, physically and chemically stable. The bulk of ageing occurred within first 150 h after deposition and was attributed to oxidation and volumetric relaxation. Thermal ageing studies indicated thermal stability increased for the films manufactured at higher RF powers, with degradation onset temperature associated with weight loss shifting from 150 ºC to 205 ºC for 10 W and 100 W polyterpenol, respectively. Annealing the films to 405 °C resulted in full dissociation of the polymer, with minimal residue.

Given the outcomes of the fundamental characterisation, a number of potential applications for polyterpenol have been identified. Flexibility, tunable permittivity and loss tangent properties of polyterpenol suggest the material can be used as an insulating layer in plastic electronics. Implementation of polyterpenol as a surface modification of the gate insulator in pentacene-based Field Effect Transistor resulted in significant improvements, shifting the threshold voltage from + 20 V to –3 V, enhancing the effective mobility from 0.012 to 0.021 cm²/Vs, and improving the switching property of the device from 10⁷ to 10⁴. Polyterpenol was demonstrated to have a hole transport electron blocking property, with potential applications in many organic devices, such as organic light emitting diodes.

Encapsulation of biomedical devices is also proposed, given that under favourable conditions, the original chemical and biological functionality of terpinen−4−ol molecule can be preserved. Films deposited at low RF power were shown to successfully prevent adhesion and retention of several important human pathogens, including P. aeruginosa, S. aureus, and S. epidermidis, whereas films deposited at higher RF power promoted bacterial cell adhesion and biofilm formation. Preliminary investigations into in vitro biocompatibility of polyterpenol demonstrated the coating to be non−toxic for several types of eukaryotic cells, including Balb/c mice macrophage and human monocyte type (HTP−1 non-adherent) cells. Applied to magnesium substrates, polyterpenol encapsulating layer significantly slowed down in vitro biodegradation of the metal, thus increasing the viability and growth of HTP−1 cells. Recently, applied to varied nanostructured titanium surfaces, polyterpenol thin films successfully reduced attachment, growth, and viability of P. aeruginosa and S. aureus.

Item ID: 29891
Item Type: Thesis (PhD)
Keywords: organic electronics; thin film; flexible electronics; polyterpenol films
Additional Information:

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

Chapter 1. Jacob, Mohan, and Bazaka, Kateryna (2010) Fabrication of Electronic Materials from Australian Essential Oils. Report. Australian Government: Rural Industries Research and Development Corporation, Barton, ACT, Australia.

Chapter 2. Bazaka, Kateryna, Crawford, Russell J., and Ivanova, Elena P. (2011) Do bacteria differentiate between degrees of nanoscale surface roughness? Biotechnology Journal, 6 (9). pp. 1103-1114.

Chapter 2. Bazaka, Kateryna, Crawford, Russell J., Nazarenko, Evgeny L., and Ivanova, Elena P. (2011) Bacterial extracellular polysaccharides. In: Bacterial Adhesion: Chemistry, Biology and Physics. Advances in Experimental Medicine and Biology, 715 . Springer, London, UK, pp. 213-226.

Chapter 2. Bazaka, Kateryna, Jacob, Mohan V., Crawford, Russell J., and Ivanova, Elena P. (2011) Plasma assisted surface modification of organic biopolymers. Acta Biomaterialia, 7 (5). pp. 2015-2028.

Chapter 2. Bazaka, Kateryna, Jacob, Mohan V., Crawford, Russell J., and Ivanova, Elena P. (2012) Efficient surface modification of biomaterial to prevent biofilm formation and the attachment of microorganisms. Applied Microbiology and Biotechnology, 95 (2). pp. 299-311.

Chapter 3. Bazaka, K., and Jacob, M.V. (2009) Synthesis of radio frequency plasma polymerized non-synthetic Terpinen-4-ol thin films. Materials Letters, 63 (18-19). pp. 1594-1597.

Chapter 3. Bazaka, Kateryna, Jacob, Mohan V., and Bowden, Bruce F. (2011) Optical and chemical properties of polyterpenol thin films deposited via plasma-enhanced chemical vapor deposition. Journal of Materials Research, 26 (8). pp. 1018-1025.

Chapter 4. Bazaka, Kateryna, and Jacob, Mohan V. (2011) Nanotribological and nanomechanical properties of plasma-polymerized polyterpenol thin films. Journal of Materials Research, 26 (23). pp. 2952-2961.

Chapter 5. Bazaka, Kateryna, and Jacob, Mohan V. (2010) Post-deposition ageing reactions of plasma derived polyterpenol thin films. Polymer Degradation and Stability, 95 (6). pp. 1123-1128.

Chapter 5. Bazaka, Kateryna, and Jacob, Mohan V. (2012) Solubility and surface interactions of RF plasma polymerized polyterpenol thin films. Materials Express, 2 (4). pp. 285-293.

Chapter 6. Bazaka, Kateryna, and Jacob, Mohan V. (2011) Complex permittivity measurements of RF plasma polymerized polyterpenol organic thin films employing split post dielectric resonator. Journal of Polymer Engineering, 31 (2-3). pp. 73-75.

Chapter 6. Bazaka, Kateryna, and Jacob, Mohan V. (2010) Effect of iodine doping on surface and optical properties of polyterpenol thin films. Materials Science Forum, 654-656 . pp. 1764-1767.

Chapter 7. Jacob, M.V., Bazaka, K., Weis, M., Taguchi, D., Manaka, T., and Iwamoto, M. (2010) Fabrication and characterization of polyterpenol as an insulating layer and incorporated organic field effect transistor. Thin Solid Films, 518 (21). pp. 6123-6129.

Chapter 7. Bazaka, Kateryna, Jacob, Mohan V., Taguchi, Dai, Manaka, Takaaki, and Iwamoto, Mitsumasa (2011) Investigation of interfacial charging and discharging in double-layer pentacene-based metal-insulator-metal device with polyterpenol blocking layer using electric field induced second harmonic generation. Chemical Physics Letters, 503 (1-3). pp. 105-111.

Chapter 7. Bazaka, Kateryna, Jacob, Mohan V., Taguchi, Dai, Manaka, Takaaki, and Iwamoto, Mitsumasa (2011) Effect of organic gate dielectric material properties on interfacial charging and discharging of pentacene MIM device. Physics Procedia, 14 . pp. 62-66.

Chapter 7. Jacob, Mohan V., Bazaka, Kateryna, Taguchi, Dai, Manaka, Takaaki, and Iwamoto, Mitsumasa (2012) Electron-blocking hole-transport polyterpenol thin films. Chemical Physics Letters, 528 . pp. 26-28.

Chapter 8. Bazaka, Kateryna, Jacob, Mohan V., Crawford, Russell J., and Ivanova, Elena P. (2011) Plasma polymerisation and retention of antibacterial properties of terpinen-4-ol. Proceedings of the International Conference on Antimicrobial Research ICAR 2010 International Conference on Antimicrobial Research. , 3-5 November 2010, Valladolid, Spain.

Chapter 8. Bazaka, Kateryna, Jacob, Mohan V., and Ivanova, Elena P. (2010) A study of a retention of antimicrobial activity by plasma polymerized terpinen-4-ol thin films. Materials Science Forum, 654-656 . pp. 2261-2264.

Chapter 8. Bazaka, Kateryna, Jacob, Mohan V., Ivanova, Elena P., and Truong, Vi Khanh (2010) Radio frequency plasma enhanced synthesis of antifouling polymeric coatings from monoterpene alcohols. TENCON2010, 21-24 November 2010, Fukuoka, Japan.

Chapter 8. Bazaka, Kateryna, Jacob, Mohan V., Truong, Vi Khanh, Crawford, Russell J., and Ivanova, Elena P. (2011) The effect of polyterpenol thin film surfaces on bacterial viability and adhesion. Polymers, 3 (1). pp. 388-404.

Chapter 8. Bazaka, Kateryna, Jacob, Mohan V., Truong, Vi Khanh, Wang, Feng, Pushpamali, Wickrama Arachchilage Anoja, Wang, James Y., Ellis, Amanda V., Berndt, Christopher C., Crawford, Russell J., and Ivanova, Elena P. (2010) Plasma-enhanced synthesis of bioactive polymeric coatings from monoterpene alcohols: a combined experimental and theoretical study. Biomacromolecules, 11 (8). pp. 2016-2026.

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