A quantitative model for the surface restructuring of repeatedly plasma treated silicone rubber |
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Authors: | Emmanuel P Everaert Ronald C Chatelier Henny C van der Mei Henk J Busscher |
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Institution: | (1) Laboratory for Materia Technica, University of Groningen, Bloemsingel 10, 9712 Groningen, KZ, The Netherlands;(2) Division of Chemicals and Polymers, CSIRO, Private Bag 10, Rosebank MDC, 3169 Clayton, Australia |
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Abstract: | Surface restructuring in ambient air of medical grade silicone rubber surfaces modified by repeated RF plasma treatments using
various discharge gases including oxygen, argon, carbon dioxide and ammonia, was studied quantitatively. From advancing and
receding water contact angle data, the fraction of the surface covered by mobile and immobile polar groups, and a characteristic
time constant of the restructuring process were calculated. For argon plasma treated surfaces, the fraction of immobile polar
groups increased with repeated plasma treatments, but remained relatively constant for samples repeatedly treated by an ammonia
plasma. The use of an oxygen plasma only yielded incorporation of mobile polar groups but not of immobile polar groups. The
increase in the restructuring time constants of argon and ammonia plasma treated silicone rubber with the number of plasma
treatments suggested enhanced crosslinking of the silicone rubber by these plasmas. In contrast, when an oxygen plasma was
repeatedly used, the restructuring time constant decreased suggesting chain cleavage by an oxygen plasma. Tentatively, the
carbon dioxide plasma treatment of silicone rubber may initially (up to 3–4 repeated treatments) yield chain cleavage, while
the occurrence of crosslinking is indicated after more repetitions. |
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Keywords: | Plasma treatment silicone rubber water contact angle surface restructuring crosslinking chain scission |
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