Silicone Surface Science
Silicone Surface Science offers a survey of the major topics concerning the properties and behavior of silicone surfaces. It covers all main aspects of the subject, including: polydimethylsiloxane, spread monolayers, self-assembled monolayers, hydrophobic
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General Introduction to Silicone Surfaces Michael J. Owen and Petar R. Dvornic
1.1 Introduction Surface properties of silicones have been exploited from the start of the silicone industry and continue to be dominant today. According to Warrick [1] one of the most useful early applications was the treatment of glass fibers using hydrolyzed silanes to create a water-repellent product. Other early silicone products include hydrophobic greases to seal aircraft ignition systems and antifoam agents for petroleum oils. We conservatively estimate that 70 % of the current market for silicones result from their surface properties and behavior. For more information on silicone applications see Chap. 13. The term “silicone” is not a precise one. We use it to describe polymeric materials based on a silicon-oxygen backbone with organic groups attached directly to silicon atoms. These organic groups can be inert or reactive so our definition encompasses not only polydimethylsiloxane –[Si(CH3 )2 O]n – (PDMS), which continues to hold the dominant position in the silicone industry, but also other polysiloxanes such as fluorosilicones and hydrolyzed silane coupling agents. This definition does not include, nor does this volume address except in passing, other organosilicon polymers such as polycarbosilanes, polysilanes and polysilazanes. With its inorganic backbone and organic pendant groups, PDMS and other silicone polymers belong to the class of “semi-inorganic” [2] or “organo-inorganic” polymers. Superficially, the surface properties of PDMS might be expected to be an average of these two dissimilar constituents but this is not the case. For example, the surface energy and hydrophobicity of PDMS are much more akin to hydrocarbons such as paraffin wax than they are to silica. The explanation lies in two general rules, namely, the second M.J. Owen () · P.R. Dvornic Michigan Molecular Institute, 1910 W. St. Andrews Rd., Midland, MI 48640, USA e-mail: [email protected] P.R. Dvornic () e-mail: [email protected] M.J. Owen, P.R. Dvornic (eds.), Silicone Surface Science, Advances in Silicon Science 4, DOI 10.1007/978-94-007-3876-8_1, © Springer Science+Business Media Dordrecht 2012
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M.J. Owen and P.R. Dvornic
law of thermodynamics and Langmuir’s principle of the independence of surface action [3]. The second law of thermodynamics can be expressed in numerous ways. One common form is that systems will change spontaneously in the direction of minimum total free energy. Hence, for a polymer like PDMS containing both polar and non-polar entities it is axiomatic that the low-surface-energy methyl groups will accumulate in the surface and dominate surface behavior. Langmuir’s principle takes this expectation a step further. It postulates that one can conceive of separate surface energies for each of the different parts of complex molecules and that the surface energy of a material made of such molecules is determined by the composition and orientation of the outermost groups independent of the underlying components. This is t
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