Abstract
Poly(dimethylsiloxane) (PDMS), is one of the polymers with the lowest surface energy in common use, it possesses good physical and electrical properties, which, along with easy processability makes it suitable for use in a range of different industrial and domestic applications. In this study, the surfaces of two PDMS formulations have been treated with a mild, low pressure, plasma to modify the surface properties. The, normally non-adhesive, PDMS was found to adhere very well to glass substrates after plasma treatment. This study has been carried out to gain a better understanding of the physico-chemical reactions and changes that take place on the surface of plasma treated PDMS by using XPS, ToF-SIMS and AFM to characterise the PDMS surfaces. During this work, a novel approach was successfully developed using an artificial neural network to sort and classify the large number of very similar XPS spectra that resulted from the investigation of plasma treated PDMS. Peak fitting protocols have been devised for complex Cls and Si2p XPS spectra of the model and commercial PDMS, and these results correlate well with the formation of an SiOH component, identified by ToF-SIMS. The SiOH component is the main factor responsible for adhesion between plasma treated PDMS and glass. The level of adhesion achieved between the plasma treated PDMS and glass has been quantified using a modified JKR approach developed for this work, and is shown to be related to the plasma exposure time. The characterisation of the PDMS surfaces, before and after plasma treatment, has led to an understanding of the mechanism of plasma surface modifications and subsequent mechanisms of adhesion between PDMS and glass. Models for such mechanisms are proposed on the basis of spectroscopic and empirical observations.