Surface Activation of Poly(methyl methacrylate) via Remote Atmospheric Pressure Plasma Eleazar Gonzalez II, Michael D. Barankin, Peter C. Guschl, Robert F. Hicks* Introduction Poly(methyl methacrylate) (PMMA) is a polymer with many desirable characteristics. It has excellent optical properties, environmental stability, and low cost. [1] In recent years, PMMA has replaced glass products in many optical applications where high impact resistance, chemi- cal inertness, low weight, and flexibility are important. [2] In addition, PMMA can be used in optical components due to its low refractive index, high transparency in the visible region, and reduced reflection losses. [3] This polymer also finds application in biomedical devices [4] and gate dielec- trics. [5] Despite these attractive properties, PMMA exhibits a low surface energy, which can result in poor adhesion. Plasmas have been widely utilized to treat polymers and increase their surface energy. [2,3,6–22] Plasma treatment can be performed in vacuum or at atmospheric pressure. Operation at ambient pressure offers several advantages: the equipment is simpler, since it does not require chambers, load locks, or vacuum pumps. The plasma treatment can be integrated with other process steps, such as adhesive dispensing or powder spray. Moreover, in vacuum, the surface of the material is subjected to a variety of phenomena including ion bombardment, electron impact, chemical reactions, ultraviolet irradiation, implantation, and redeposition of etched species. [19] Because of the abundance of surface interactions, it can be difficult to understand the mechanism of surface modification. By Full Paper E. G. II, M. D. Barankin, R. F. Hicks Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA E-mail: rhicks@ucla.edu P. C. Guschl Surfx Technologies LLC, 3617 Hayden Avenue, Culver City, CA 90232, USA An atmospheric pressure oxygen and helium plasma was used to activate the surface of poly(methyl methacrylate) (PMMA). The plasma physics and chemistry was investigated by numerical modeling. It was shown that as the electron density of the plasma increased from 3  10 10 to 1  10 12 cm 3 , the concentration of O atoms and metastable oxygen molecules ( 1 D g ) in the afterglow increased from 6  10 15 to 1  10 17 cm 3 . Exposing PMMA to the afterglow for times between 0 and 30 s led to a 358  38 decrease in water contact angle, and a ten-fold increase in bond strength to several adhesives. X-ray photoelectron spectroscopy of the polymer revealed that after treatment, the surface carbon attributable to the methyl pendant groups decreased 5%, while that due to carboxyl acid groups increased 7%. The numerical modeling of the afterglow and experimental results indicate that oxygen atoms generated in the plasma oxidize the polymer chains. 482 Plasma Process. Polym. 2010, 7, 482–493 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ppap.200900113