Nanoindentation of Vacuum Ultraviolet Light-Irradiated Poly(methylmethacrylate) Substrates
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Nanoindentation of Vacuum Ultraviolet Light-Irradiated Poly(methylmethacrylate) Substrates
Atsushi Hozumi,1 Yoshiyuki Yokogawa,1 Tetsuya Kameyama,1 Yunying Wu,2 Hiroyuki Sugimura,2 and Osamu Takai3 1
National Institute of Advanced Industrial Science and Technology (AIST),
2266-98 Anagahora, Shimo-shidami, Moriyama-ku, Nagoya 463-8560, Japan 2
Department of Materials Processing Engineering, Graduate School of Engineering, Nagoya
University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. 3
Center for Integrated Research in Science and Engineering, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. ABSTRACT Surface modification of poly(methylmethacrylate) (PMMA) substrates has been demonstrated using an excimer lamp radiating vacuum ultraviolet (VUV) light of 172 nm in wavelength. In this study, we have particularly focused on the effects of atmospheric pressure during VUV irradiation. Each of the substrates was photoirradiated with VUV light under a pressure of 10, 103 or 105 Pa. Changes in nanomechanical properties of the VUV-irradiated sample surfaces were studied based on a scratching test using a nanoindenter. The wear-depth of the PMMA sample treated at 105 Pa was about 137.0 nm, which was much larger than the wear-depth of an untreated PMMA substrate (63.3 nm). On the contrary, when samples were prepared with VUV irradiation conducted at 10 and 103 Pa, their wear-depths markedly decreased down to about 2.2 and 12.5 nm, respectively. The sample treated at 10 Pa was particularly wear-resistant. This high wear-resistance was attributable to the formation of new carbon-carbon bonds such as C=C bonds on the PMMA surfaces. INTRODUCTION The surface modification of polymeric materials through vacuum ultraviolet (VUV) light irradiation has attracted much attention due to its wide variety of applications, including microstructure fabrication, photochemical etching, and improvement of the wettability,
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biocompatibility and coating adhesion of such surfaces [1-3]. There have been reports on the chemical properties of VUV-irradiated polymer substrates, however, their nanomechanical properties have not been studied in detail [4]. Here we report on changes in nanotribological properties of poly(methylmethacrylate) (PMMA) substrates after 172 nm VUV irradiation based on a scratching test using a nanoindenter connected to an atomic force microscope (AFM), as well as on changes in their chemical structures. We have particularly focused on the effects of atmospheric pressure during VUV irradiation, since atmospheric oxygen plays a crucial role in the photochemical reactions of polymeric materials. EXPERIMENTAL DETAILS
Sample substrates of 10 10 1.1 mm3 cut from a commercial PMMA sheet (Asahi KASEI Co., Delaglas®A) were photochemically modified. Each of the samples was placed in a vacuum chamber evacuated by a rotary pump. The pressure in the chamber was controlled at 10, 102 or 103 Pa by introducing air through a variable leak valve or at 105 Pa without evacuation. The PMMA substrate wa
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