Characterization of thin silicone films formed by migration across defined polymer substrates

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Virginia Polytechnic Institute and State University


While theoretical treatments of liquid spreading on solid surfaces can be found in abundance in the literature, relatively few experimental studies have been performed. This study focused on the experimental detection of polydimethylsiloxane spreading on polymer surfaces in the spreading regime where gravitational and inertial forces are negligible. The techniques of x-ray photoelectron spectroscopy (XPS), reflection absorption spectroscopy (RAS), and contact angle analysis were used to investigate this problem. XPS analysis indicated that the surface spreading or "creeping" was very slow, moving only several centimeters per several hundred hours in some cases. An interesting observation was that the spreading film seemed to reach a "steady state" concentration when covering an area. Similar results were seen for both horizontal and vertical substrate surfaces with XPS, and there seemed to be a substrate dependence. Angular-dependent XPS analysis revealed that the film was very thin (<20A) and not a complete layer. Contact angle analysis was used to monitor the siloxane movement, although there was a contact angle dependence on x-ray exposure time, indicating cross-linking of the surface film. Contact angle variations were also used to show that the film characteristics may be dependent on the nature of the polymer substrate. Reflection absorption spectroscopy was used to investigate thin substrate polymer films, and it was shown that theoretical predictions of absorption band intensity correlated reasonably well with the experiment. This technique was also used to investigate the surface siloxane layer and indicated that under some conditions, the orientation of the surface silicone layer may be occurring.