Surface Chemistry Modification
Plasma treatment can be applied to alter surface chemistry in materials through functional groups introduced by the plasma gas. This application note discusses the benefits of plasma treatment for controlling surface properties, plasma processing guidelines, and examples of the effect of surface chemistry and contact angle on plasma-treated materials.
plasma cleaners for surface modification, see the Surface Modification and Surface Wettability categories in our Technical Library.
Benefits of Plasma Cleaning
- Render surfaces hydrophilic by oxidation and formation of hydroxyl (OH) groups
- Render surfaces hydrophobic with deposition of fluorine-containing groups (CF, CF2, CF3)
- Pattern alternating hydrophilic/hydrophobic regions on surfaces for self-assembly studies
- Graft functional polymers or end groups onto plasma-activated surfaces [Figure 3]
- Promote adhesion of cells and cell proliferation on plasma-modified biomaterials or tissue scaffolds
- Deposit polymer layers by plasma polymerization
Water vapor (H2O) can also be used to introduce hydroxyl groups and render surfaces more hydrophilic. Special gas delivery equipment and gas handling procedures would be required to use with the plasma system. For samples that are sensitive to moisture, H2O plasma would not be recommended.
Alternatively, an argon plasma may be preferred for surface activation to minimize further oxidation of surfaces (e.g. metals). Argon plasma cleans by ion bombardment and physical ablation of contaminants off the surface and can also increase surface hydrophilicity by reaction of the plasma activated surfaces upon exposure to ambient air.
Carbon tetrafluoride (CF4) plasma may be applied on surfaces to form a hydrophobic coating of fluorine-containing groups (CF, CF2, CF3). The fluorinated plasma decreases the number of hydrophilic polar end groups on surface and decreases surface wettability. Use of fluorinated gas requires replacing the standard pyrex chamber with a quartz chamber.
In addition, applications that are sensitive to potential contamination from trace impurities in borosilicate glass may also benefit from a quartz chamber substitution.
Below are suggested process conditions for plasma cleaning in a Harrick Plasma cleaner (some experimentation may be required to determine optimal process conditions):
- Pressure: 100 mTorr to 1 Torr
- RF power: MEDIUM or HIGH
- Process time: 1-3 minutes
- Surfaces should be used immediately after plasma treatment; plasma-treated surfaces may recover their untreated surface characteristics with prolonged exposure to air