Improved Substrate Protection and Self-Healing of Boundary Lubrication Film Consisting of Polydimethylsiloxane with Cationic Side Groups |
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Authors: | Erik Hsiao Laura C Bradley Seong H Kim |
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Affiliation: | (1) Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, USA; |
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Abstract: | The substrate protection and self-healing capability of a cationic polymer lubricant (CPL) on a silicon oxide surface were
tested with a pin-on-disc tribometer and atomic force microscopy (AFM). CPL was made of low molecular weight polydimethylsiloxane
(PDMS) containing covalently attached quaternary ammonium cations and iodide counter-anions. CPL was spin-coated on the silicon
oxide surface to form a 3–4 nm thick bound-and-mobile lubricant layer. The CPL film capable of binding to the SiO2 surface through ionic interactions is superior in substrate protection than the neutral PDMS film which cannot form the bound
layer. The mobile component in the CPL film readily flows into the lubricant-depleted sliding contact region from the surrounding
film. The self-healing capability of CPL via lateral flow is slightly enhanced in humid environments due to water uptake in
the film. The 3–4 nm thick CPL film on silicon oxide takes 30–40 s to flow into a ~50 μm wide track, which corresponds to
an apparent spreading rate of 2–3 × 10−11 m2/s. |
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