1710 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 33, NO. 5, OCTOBER 2005 Dielectric Barrier Discharge Technique in Improving the Wettability and Adhesion Properties of Polymer Surfaces Nicoleta Dumitrascu, Ionut Topala, and Gheorghe Popa Abstract—A dielectric barrier discharge (DBD) in helium at at- mospheric pressure was used to improve the polymer surface wet- tability as a first condition for ensuring a good adhesivity in partic- ular for a subsequent immobilization of selected biological macro- molecules (heparin, drugs, enzymes, etc.) on these surfaces. The DBD was analyzed by electrical measurements and optical emis- sion spectroscopy. The polymer surface was characterized by ther- modynamic parameters which may predict the adhesion proper- ties, the adhesion work and the surface polarity, and also by its morphology. The results show that the DBD treatments improve the wettability and thus the adhesive properties due to the creation of functional groups and less due to a physical adsorption induced by an expected larger area of the treated surfaces. Dimensions of grains/crystallites are decreased on the treated surface, but a sig- nificant and systematic modification of the surface roughness was not observed. Index Terms—Adhesion properties, dielectric barrier discharge, filamentary mode, functionalization, morphology, polarity, polymer surfaces, roughness, wettability. I. INTRODUCTION D IELECTRIC barrier discharges (DBDs) are transient glow discharges which can operate at low or atmospheric pres- sure between two electrodes electrically insulated from the dis- charge gap by one or more dielectric materials (dielectric bar- rier). Lately, the DBD at atmospheric pressure became one con- venient technique for mechanical and physico-chemical surface modification [1]–[4]. In particular, DBD can be an efficient tech- nology for various medical applications, i.e., in immobilizing specific biological molecules on the implant surfaces [5] or in decontamination of biological media (germicidal effects) [6]. Compared to other plasma processing techniques, the DBD has some advantages such as, works well at atmospheric pressure, without vacuum restrictions, has simple and flexible configura- tions with respect to the geometrical shape of electrodes and the gap, and can treat surfaces of various sizes and shapes and online surface treatments are possible. Finally, the DBD technique has high efficiency and speed processing, very low electric power input, and excellent operational cost. The DBD treatments induce various modifications on the polymer surfaces ranging from simple cleaning and mor- phological changes to functionalization, crosslinking, and surface chemistry modification [7], [8]. Usually, the polymers Manuscript received December 11, 2004; revised June 21, 2005. This work was supported in part by the Romanian National University Research Council (CNCSIS) under Grant 1344/2003–2005. The authors are with the Faculty of Physics, “Al. I. Cuza” University, Iasi, 700506 Romania (e-mail: nicole@uaic.ro). Digital Object Identifier 10.1109/TPS.2005.856335 used in medicine and biology have excellent mechanical and physico-chemical properties for medical devices but their biocompatibility is poor at the contact with the biological environment. One of the practical solutions to enhance the biocompatibility of the polymers with the human is to mediate this interface by covering the polymer surface with specific biological layers, either to prevent coagulation (heparin) or infection (antibiotics) or/and even by covering the implant surface with endothelial cells [9]–[11]. Unfortunately, due to their low surface energy and poor wettability, the polymeric surfaces are not suitable for these types of coatings and one of the solutions is to increase the surface energy by plasma pretreatments, keeping the bulk properties unchanged. In our experiments, a DBD in helium at atmospheric pressure was used to improve the wettability of polymer surfaces by creation of functional groups on these surfaces. The synthetic polymer surfaces that were treated were selected for their potential in medical applications: polyvinylchloride (PVC), polyamide (PA-6), polyethylene terephtalate (PET) and polyethylene terephtalate with some percents of titanium dioxide , polymethylmethacrylate (PMMA), and polytetrafluorethylene (PTFE). PVC is one of the most widely used thermoplastic polymer in medical devices due to its flexibility, strength, chemical re- sistance, low cost, and easiness to sterilize and handle. PVC is used for blood and intravenous bags, catheters, dialysis tubing, inhalation masks, packaging, splints, etc. PA-6 is a semicrys- talline polymer with high toughness, low friction coefficient, high tensile strength, low density, and good resistance at heat and solvents. PA-6 foils are used for orthopedic implants, catheters, membranes for reverse osmosis, ultrafiltration and electrodial- ysis or as monofilaments in nonabsorbable sutures. PET is also a semicrystalline polymer which has the higher stretch strength compared to all thermoplastics and it is used as suture filaments, vascular grafts, packing foils, and as magnetic video and indus- trial tape, too. The has photolytic and hydrophilic effects due to the presence as pigments which strongly ab- sorb the radiation close to ultraviolet region. PMMA is charac- terized by very good light transmittance, toughness and stability, and it is a preferred material for applications in ophthalmology, for intra-ocular and contact lens. PTFE is a semicrystalline, white and opaque polymer, with excellent mechanical properties and high chemical resistance, having a very low refractive index and the lowest known dielectric constant of all plastics; it is used in orthopedic implants and also for vascular grafts. The aim of our experiments is to demonstrate the efficiency of the DBD treatments for the improvement of the adhesion prop- 0093-3813/$20.00 © 2005 IEEE