A. Michelmore, D.A. Steele, J.D. Whittle, J.W. Bradley,
R.D. Short
University of South Australia Based upon review article
RSC Advances, 2013, 3, 13540-13557
Tutorial on Plasma Polymerization
Deposition of Functionalized Films
Mawson Institute
Tutorial covers
• Introduction – Technological importance of plasma polymers + examples
• The plasma phase
– Plasma – surface interactions
– Mechanisms of deposition
- examines W/F - early stages of film grow - the role of ions
Introduction to Plasma polymerization
• Plasma ignited in organic vapour
– Pure vapour or a mixture of vapours
– Reduced pressure
• Polymer (organic) deposit formed on all surfaces
• Chemistry of deposit often similar to vapour (monomer)
– Polymerisation not dependent on functional group
– Plasma polymers tailored from organic to “inorganic”
General properties of plasma polymers
• Ultra-thin (< 50nm)
• Soluble/Insoluble
• Trapped free radicals
• Adherent
• Conformal
• Pinhole free
• Internal stress – Will crack and flake if too thick
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Plasma polymerization is the ultimate enabling technology
Hydrophobic/Hydrophobic
Functionalized films Chemical Gradients
Responsive “intelligent” surfaces
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Example - Super hydrophobic coatings
• Produced by pulsed plasma polymerization - Highly fluorinated monomers, e.g. TFE • Large amount of conventional PTFE in ‘ribbons’
- Rough surface • In continuous wave mode no ‘ribbons’ on surface
- Ribbons grow in ‘off’ period from activated sites
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Example - Treatment of Burns
• In myskinTM technology a plasma polymerized coating is applied to a bandage to allow the culture of patient’s own cells
• Cells are delivered “off” pp-coated bandage
- Highly effective way of getting cells to patients rapidly
- Used in treatment of severe burns
• Range of potential applications
Haddow et al., Plasma Processes Polym., 2006, 3, 419
Renaissance in plasma polymerization:
• Traditionally, <1990s, scratch resistance, barrier layer, wetting – E.g. Nature, 1966, 209, 769
• Recent-cited applications: - Coating of tissue engineering scaffolds (Adv. Mater., 2006, 18,1406)
- Functionalization of nanotubes for covalent coupling of quantum dots (Adv. Mater., 2007, 19, 4003)
- Fabrication of a microcantilever fast humidity sensor (Adv. Mater., 2007, 19, 4248)
- Micro- and nano-engineering of surface structures (Adv. Mater., 2006, 18, 1406; Adv. Mater., 2007, 19, 1947; Adv. Mater., 2010, 22, ,
1451)
- Surfaces for high-throughput screening devices (Adv. Mater., 2008, 20, 116; Lab on a Chip, 2011, 11, 541)
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Making a plasma polymer
What do you need to start?
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Reactor
• Enclosed chamber
- Means to introduce monomer as vapour
- Reduced pressure ~1Pa – 100Pa
- (~0.75 mTorr- 75mTorr)
• Method of excitation DC or AC (RF→MW), CW or pulsed
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RF excitation preferred for plasma polymers
• Electric fields heat electrons, generate plasma
–See Tutorial 2 – The Plasma Phase
• Advantages of RF
–Displacement rather than particle currents
–Stability
–Higher electrons temperature
–Process insulating materials without sputtering at electrodes
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Plasma polymerization:
Plasma Chamber (under vacuum)
Substrate
Gas (Monomer Vapour) Flows into Chamber
Plasma
Radiofrequency Power Applied to System
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(a) Clark and Dilks reactor design 1977 [ref 18] and three decades of reactor design evolution since, illustrating a variety of electrode configurations, power supplies and diagnostic tools (b) Ward 1989 [19] (c) Lopez et al. 1992 [20] (d) O’Toole et al. 1995 [21] (e) Favia et al., 1996 [22] (f) Candan et al. 1998 [23] (g) Alexander et al. 1998 [24] (h) Voronin et al. 2006 [25]
A. Michelmore et al, RSC Advances, 2013, 3, 13540
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Reactor design – Historical Perspective
Gas (Monomer)
Ions Photons Fragments
Electrons
Intact Monomer Atoms Radicals
Oligomers
Metastables
Energy transfer Chemical modification (Deposition Adsorption Grafting)
Desorption Etching
Plasma phase interactions:- Excitation, Ionisation, Relaxation, Ion-Molecule, Radical-Neutral, Fragmentation
Plasma polymerization
Substrate
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Different types of coating
Plasma parameters:
Non-functionalized Functionalized
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RF Power, Gas Flowrate, Pressure, Ion Density Electron Temperature, Bias Potentials etc