Changes of Wettability and Surface Energy of Polymer by keV Ar + Ion Irradiation
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ABSTRACT Surface modification of polycarbonate(PC) was performed to improve the wettability by Ar+ ion irradiation with I keV energy in oxygen environment. The ion dose ranged from 5 X 1014 to 5 x 1016 ions/cm 2 and oxygen flow rate was also varied from 0 to 6 sccm(ml/min.). Contact angle was not much decreased from 780 to 480 for water and from 630 to 32' for formamide by
Ar+ ion irradiation without oxygen gas, but largely reduced to 120 for water and to 80 for formamide as Air ion irradiation with 4 sccm oxygen gas. Surface energy of modified PC surface which was irradiated with oxygen gas was more increased than that of PC surface irradiated without oxygen gas. It is evident that the increase of surface energy for PC modified with oxygen gas is due to hydrophilic group which result from the chemical reaction between PC surface and oxygen gas. From X-ray photoelectron spectroscopy(XPS) analysis, the newly formed hydrophilic group is identified as hydrophilic C=O bond, and atomic force microscope(AFM), it is found that the root mean square of surface roughness is changed from 14 A to 22 - 26 A for Ar+ ion irradiation only and 26 - 30 A for Ar' ion irradiation with 4 sccm oxygen gas. Therefore wettability of PC surface is much more affected by newly formed hydrophilic group than surface roughness in keV energy Arl ion irradiation.
INTRODUCTION A large amount of interest has developed in the chemical and/or structural modification of polymer surface by bombardment with ionized gas molecule of plasma, corona, arc discharge, dc/rf sputtering etching, y-ray, a few MeV and 100s keV energy, etc.'-12 This interest has been particularly motivated by interfacial properties and technological applications such as adhesion to metal, wettability, solubility, textile, printing, etc. Many extensive studies have also been reported about improving wettability of polymer by using ion beam modification with a few MeV and 100s keV energy.9-12 But in case of these methods, high energetic ions penetrate into bulk of polymer, affecting bulk properties of polymer and main effects of these methods are chain scission, crosslink, change of surface morphology, chemical reaction etc. For plasma, corona, arc discharge13-6 which use comparably lower energetic ions than a few MeV and 100s keV energy ion beamr, they have advantages as below: (1) their reactions are limited in surface region of polymer, (2) they have chemical flexibility in terms of the choice of reactant or mixtures for producing reactive species to create various surface states. But these techniques also have results similar to those of a few MeV and 100s keV energy ion beam. Therefore new method that uses low energetic ions not to change bulk properties of polymer and generates chemical reaction which play an important role in improving surface characteristics of polymer, has been required. In this article, we show the improvement of wettability of polycarbonate(PC) by I keV Ar+ ion irradiation with various oxygen environment, and investigate the reciprocal effects of chemical
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