AVS 60th International Symposium and Exhibition
    Advanced Surface Engineering Wednesday Sessions
       Session SE+PS-WeA

Paper SE+PS-WeA4
Correlation of Spectral Emissions of a He-O2 RF Atmospheric Plasma Discharge with Polymer Surface Activation

Wednesday, October 30, 2013, 3:00 pm, Room 203 C

Session: Atmospheric Pressure Plasmas
Presenter: V. Milosavljevic, University College Dublin, Ireland
Authors: V. Milosavljevic, University College Dublin, Ireland
M. Donegan, University College Dublin, Ireland
P.J. Cullen, Dublin Institute of Technology, Ireland
D.P. Dowling, University College Dublin, Ireland
Correspondent: Click to Email
Atmospheric pressure non-thermal helium plasma jets are increasingly used in many processing applications due to their combination of inherent plasma stability and excellent reaction chemistry. Despite their widespread usage, it remains largely unknown whether cold atmospheric plasma jets maintain characteristics, such as gas temperatures and particle flux, when they breakdown while arcing or whether they possess different operating modes. From an application point of view, the activation of polymer surfaces can help to overcome the chemical inertness and low surface energy generally associated with these types of materials. Polymers, such as PET, are thermally damaged at relatively low temperatures and so a delicate balance must be reached where surface activation of the polymer is maximised, while thermal damage is prevented.

The atmospheric plasma system employed generates plasma using He-O2 (in the range of 100-200 W), operates at a frequency of 27.12 MHz and uses a 5 cm wide beam applicator. The input variables on this system were: helium gas at a constant flow rate of 30 l/min, while secondary gas input: plasma power ratios are set by the manufacturer.

This work employs optical emission spectroscopy as a diagnostic technique for the measurement of atomic and molecular spectral emissions generated using the plasma jet system. The OES of neutral atomic spectral lines and molecular bands are investigated over a range of plasma process parameters. Wavelength resolve optical emission profiles suggest that the emission of helium's spectral lines shows that the high energy electrons have a larger influence than helium metastables on the overall spectral emission. Furthermore, the experimental data indicates that the use of high helium flow rates limits the significance of air impurities, e.g. N2, for the creation and sustainability of plasma discharges in He-O2 gas chemistry. The level of polymer surface activation was evaluated based on changes to the water contact angle of PET samples after plasma treatment. For the first time a direct correlation was obtained between polymer water contact angle changes and the OES measurement of the atomic hydrogen Balmer Hα and molecular OH line emission intensities. Further work will be presented how the high helium flow rate is used in an attempt to minimize the ratio of gas convection to chemical reaction time scale (recombination). This is also favours the rapid transport of newly created radicals and excited species to the surface under treatment.

This work was a funded by SFI under the Precision cluster, the ’Fresh-Pack’ project funded by the National Development Plan of Republic of Ireland and grant OI171006.