Polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen for improving wettability

Issue		Eur. Phys. J. Appl. Phys. Volume 28, Number 1, October 2004


Page(s)		105 - 112
Section		Plasma, Discharge and Processes
DOI		10.1051/epjap:2004160
Published online		25 June 2004

Eur. Phys. J. Appl. Phys. 28, 105-112 (2004)
DOI: 10.1051/epjap:2004160

Polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen for improving wettability

P. Svarnas^{1, 2}, N. Spyrou¹ and B. Held²

¹ Electrotechnic Materials Laboratory, Electrical and Computer Engineering Department, University of Patras, 26500 Patras-Rio, Greece
² Laboratoire d'Électronique des Gaz et des Plasmas, Université de Pau et des Pays de l'Adour, CURS, avenue de l'Université, 64000 Pau, France

svarnas@ee.upatras.gr
bernard.held@univ-pau.fr

(Received: 1 July 2003 / Received in final form: 16 March 2004 / Accepted: 30 March 2004 / Published online: 25 June 2004 )

Abstract
An effort for better understanding of main parameters influence to polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen is attempted. Voltage-current curves and discharge repetitive current impulses for various gap lengths and gas pressures, in absence and in presence of polystyrene thin films in the cold plasma reactor, evidence that in any case a normal glow discharge regime is established. Atactic polystyrene thin films underlie treatment under the above regime and hydrophilic surfaces are obtained. Wettability is characterized, under certain experimental protocols, by contact angle measurements along the films treated for various gap lengths ( d=0.5, 1, 2 cm), gas pressures ( p=2-10 mbar), gas flow rates ( Q=1-1110 sccm) and times ( t_tr=0-600 s). The best treatment takes place opposite to the point electrode, in an area around the discharge symmetry axis, proving non-homogeneous surface treatment. Atomic Force Microscopy (AFM) shows that this fact does not relate to surface morphological changes. The experimental results confirm that the above treatment yields polystyrene films with very good wettability (typical contact angles: 5 ${-}15^{\circ})$ avoiding any obvious material degradation. Ageing effects are introduced but the final wettability in comparison to that before the treatment is increased. The role of excited neutrals and reactive particles with long radiative lifetime (metastables states) is emphasized and seems to lead to polymer treatment through diffusion mechanisms.

PACS
52.75.-d - Plasma devices.
81.65.-b - Surface treatments.
68.37.-d - Microscopy of surfaces, interfaces, and thin films.

© EDP Sciences 2004

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