Modification of the Wettability of Plexiglas and Carbon by Means of Ion Beam Implantation: Application to Fluid Manageme
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configuration of liquids in space [4,5]. There is also evidence that the difference between the ACA and RCAiAdvancing causes changes in the propagation of perturbation at the liquid-air interface [5]. Therefore, there is a strong interest in the modification of wetting properties for fluid material and management The processing in microgravity. use of low energy (-500 eV) ion beams is attractive. Combining their low mean range (a few nm), erosion rate and fluence they allow the possibility to modify the surface composition at will.
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DROP DIAMETER (ram) Figure 1: Example of the hysteresis of the contact angle.
EXPERIMENT Choice of samples and ions Plexiglas was chosen because the observation of the response of liquids during microgravity experiments requires containers made of transparent materials. Typically, the contact angle of water onto plexiglas is - 620 in receding and 850 in advancing. For experiments for which chemical compatibility is important, it may be advantageous to cover the plexiglas surface with a thin carbon coating (600 in receding and 780 in advancing). These reasons have brought us to conduct our surface modification experiments on carbon coatings and plexiglas samples. Plexiglas samples have been cut of a sheet and ultrasonically cleaned in ethanol. Carbon films were deposited by sublimation of carbon filament under a base pressure of -1.x]0"7 Torr. Micronuclear analyses (RBS, ERD ExB [6]) showed that no other element but hydrogen (HIC=0.2) is included in the carbon films. No significant roughness was seen by means of optical microscopy. The idea is to implant low energy ions onto the surface in order to modify the surface composition and/or to alter the molecular bonds at the surface. The former can be achieved by the implantation of active ions (N, 0) while the latter can be obtained by bombarding the surface by means of either active (N, 0) or inert (Ne) ions. Active ions will form new bonds with the elements at the surface while inert ions will break existing bonds (leading to the formation of new links) without modification of the surface sample. The use of either active or inert ions will help us to identify eventual mechanisms leading to the modification of wetting properties. Implantation It is well known that implanted ions are distributed in depth and are not present in a large fraction at the surface. Fortunately, low energy ions, on the one hand, are trapped close to the surface and, on the other hand, can erode strongly the atoms at the surface. Thus, the surface moves nearer and nearer to the mean depth of implanted ions. This is illustrated in figure 2. An appropriate selection of energy and fluence of the impinging ions allow the possibility to alter the surface composition and could result in the modification of the wettability of the surface. The samples were introduced into the implantation chamber where the base pressure was - 5.x10s Torr. They were implanted at
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