Modification of Wetting Property of Polycarbonate by Means of Ion Beam Implantation and Storage in Different Gas Environ
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Mat. Res. Soc. Symp. Proc. Vol. 504 ©1998 Materials Research Society
EXPERIMENT Materials Only commercial polycarbonate (LEXAN) was used in the CH3 I,- -\ o surface modification experiments. The repeat units of this polymer n II _ • is shown in Figure 1. The PC samples have been cut of a sheet in blocks of 10 x 10 x 3 mm3 and ultrasonically cleaned in ethanol and CH33 dried withmicroscopy. soft paper. The surfaces were also examined by means F Figure 1. The repeat units of of optical polycarbonate (PC).
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Implantation
The samples were introduced into the implantation chamber where the base pressure was -2x10 7 torr. All samples were implanted at room temperature with nitrogen (N2÷)ions to an energy of 500 eV/atom and a fluence of 5xl016 atom/cm 2 .The mean range and the standard deviation of the N ion distribution in the PC were calculated by means of the Monte Carlo code TRIM95 [4] and are 34 A and 16 A, respectively. After the implantation, the samples were stored during I to 25 hours either in different gas environments (nitrogen, oxygen, dry air and argon) directly in the implantation chamber at atmospheric pressure or under vacuum. Some samples were taken out of the vacuum chamber immediately after the implantation (nitrogen was used to fill up the chamber) and put in room air. Contamination The samples put under vacuum were slightly contaminated by polydimethylsiloxane (PDMS). PDMS is an usual contaminant in vacuum chamber and was clearly identified only by means of ToFSIMS. Using contact angle measurements and the relationship relating apparent contact angle to the chemical composition of a surface (cos 0 = f1cosO1 + f2cosO2), an average fraction of 15% PDMS was deduced. This contamination has a small effect on the contact angles (-50) and XPS measurements and its contribution was subtracted from the contact angle measurements (adjusted contact angles) and the atomic concentration ratios obtained by XPS. However, the presence of PDMS doesn't allow the sample characterization by Tof- SIMS. So, the samples were cleaned by means of hexane to remove the PDMS. XPS measurements have insured that this cleaning procedure has no noticeable effect on the PC surface composition. Surface analysis I. Contact angle. Wettability, before and after treatment, was characterized by the measurement of the contact angle hysteresis (ACA and RCA) of a drop of distilled water (surface tension = 72mTJ/mr) is deposed on the sample surface [5]. The maximum volume of the drop was 10 itd and the injection and suction speed was 6 hlI/min. II. XPS. The surface composition was determined by XPS (model ESCALAB 220i-XL) equipped with a non-monochromatic Al Ka (1486,6 eV) source at a power of 4.05 W/mm2 (15 kV, 27 mA) and a large area XL. The surface charge compensation was achieved by using a low-energy (6 eV) electron flood gun and by covering the sample with a metallic ring. The total pressure in the main vacuum chamber during analysis was typically 9x10 9 torr. For each sample, a detail scan of C Is, 0 Is and N Is was performed by
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