Dielectric barrier discharge (DBD) processing of PMMA surface: Optimization of operational parameters

• Published in: Surface & coatings technology 2006-12, Vol.201 (6), p.2341-2350
• Main Authors: Liu, Chaozong, Brown, Norman M.D., Meenan, Brian J.
• Format: Article
• Language: English
• Subjects: Atmospheric plasma processing; Cross-disciplinary physics: materials science; rheology; Dielectric barrier discharge; Exact sciences and technology; Materials science; Other topics in materials science; Physics; Poly(methyl methacrylate) (PMMA); Statistical analysis; Surface modification
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2006.04.001

This paper reported the effects that the key dielectric barrier discharge (DBD) operating parameters, discharge power, processing speed, processing duration and electrode configurations, have on producing wettability changes and on uniformity in the PMMA surface region. The results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the PMMA surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to sites in orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, the resultant surface shown higher standard deviation (S.D.) of contact angle in T-direction than that in L-direction. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the discharge power used were found to have the most significant effects on the homogeneity of the resultant PMMA surface changes in L- and T-orientation, respectively. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PMMA surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicone rubber-covered aluminium plate. The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. It was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation within the test range employed, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater chan