Surface Modification of a Group of Polymers Using a Low Temperature Cascade Arc Torch Mary Gilliam, Qingsong Yu Center for Surface Science and Plasma Technology, Department of Chemical Engineering, University of Missouri-Columbia, Columbia, Missouri 65211 Received 30 June 2006; accepted 16 December 2006 DOI 10.1002/app.26054 Published online 13 March 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Surface modification treatments were per- formed on six different types of polymers using low tem- perature cascade arc torch (LTCAT) of Ar with or without adding reactive gas of O 2 or H 2 O vapor. The effects of the treatments on the wettability enhancement, surface degra- dation from oligomer formation, and surface stability from the mobility of surface moieties and hydrophobic recovery were investigated. Surface characterization techniques included the static Sessile droplet method and dynamic Wilhelmy balance method. Experimental results indicated that Ar LTCAT treatments of the polymers with shorter treatment times (2 s in most cases) resulted in stable and hydrophilic surfaces without any surface damage from oligomer formation, with the exception of nylon-6. The excellent results from Ar LTCAT treatments were attrib- uted to the CASING effect (crosslinking via activated spe- cies of inert gas). Addition of O 2 into Ar LTCAT resulted in greater wettability of the treated surfaces, but increased surface damage from oligomer formation. Adding H 2 O vapor into Ar LTCAT produced extremely hydrophilic surfaces on the polymers, but pronounced surface damage. The surface oligomer formation was attributed to alkoxy degradation reactions and chain scission from overexpo- sure to high energy species. Comparisons of the treatment outcomes for each type of polymer are discussed with respect to the degree of wettability enhancement, the sta- bility of the treated surfaces, and the susceptibility to de- gradation. Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 360–372, 2007 Key words: surface modification; plasma treatment; cas- cade arc torch; contact angle; Wilhelmy; polymethylmetha- crylate; polystyrene; polycarbonate; polyoxymethylene; sili- cone rubber; nylon-6 INTRODUCTION Plasma treatments have found wide applications in surface modification of polymers to improve their adhesive properties, enhance wettability, biocom- patibility, barrier properties, optical reflection, suscep- tibility to harsh agents, and to reduce friction, among other objectives. 1–7 Plasma techniques offer advan- tages over other techniques because of the effec- tiveness and versatility of the treatments and the environmentally benign nature of the plasmas. How- ever, traditional plasma techniques involve surface bombardment by high-energy species, such as ions, electrons, and VUV/UV photons, which can bring about significant degradation on the polymer surfaces. In addition, the complex nature of the plasma makes it difficult to selectively isolate beneficial surface reaction mechanisms and minimize detrimental effects. Much is still unknown regarding the complex reaction mechanisms at the plasma–polymer inter- face during plasma surface modification. Consequen- ces of plasma treatments used for chemical modifica- tion (excluding deposition processes) include surface functionalization, in which new surface functional groups are created, surface crosslinking by the CAS- ING (Crosslinking via Activated Species of INert Gases) effect, etching of surface material into volatile species, and the scission of surface polymer chains into loosely-bonded oligomers or Low Molecular Weight Oxidized Material (LMWOM). 8 The degrada- tion of a polymer surface into a layer of oligomers can occur from bombardment of high-energy species that induce chain scission or via the formation and degradation of alkoxy radicals. The alkoxy degrada- tion reaction is shown below, which results in scis- sion of a polymer chain: alkoxy degradation : R 1 CCðO  ÞR 2 ! R 1 C  þ R 2 C ¼¼¼ O ð1Þ Alkoxy radicals can be formed on polymer surfaces in the presence of oxygen-containing plasmas through several routes originating from reactions with oxidizing species, such as O 2 , O, O 3 ,H 2 O 2 , HO 2 , and OH. 9 Plasma surface modification studies have found that the outcome of the treatment depends on the Correspondence to: Q. Yu (yuq@missouri.edu). Contract grant sponsors: Faculty Startup Funds of Col- lege of Engineering, Research Council of University of Missouri-Columbia. Journal of Applied Polymer Science, Vol. 105, 360–372 (2007) V V C 2007 Wiley Periodicals, Inc.