Improved Substrate Protection and Self-Healing of Boundary Lubrication Film Consisting of Polydimethylsiloxane with Cationic Side Groups

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 boundand-mobile lubricant layer. The CPL film capable of binding to the SiO 2 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 selfhealing 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 lm wide track, which corresponds to an apparent spreading rate of 2-3 9 10 -11 m 2 /s.

Boundary lubrication by adsorption film

“…There are some other types of SAMs, such as polymer brushes, charged (polyelectrolyte) [25,26] or neutral [27], adsorbed or grafted, on a solid surface [28], each of which has its own special tribological properties related to its unique structure. There was also an attempt to form an ionically bound polymer layer and mobile multilayer with self-healing effect to provide robust and long-lasting boundary lubrication performance [29].…”

Self-healing and self-repairing technologies

“…An example of a strategy to prevent MEMS failure is the use of a surface lubricant [139]: silicon oxide surfaces which rub against each other get easily damaged, and a lubricant could protect them. Three ways for applying polymer lubricants are investigated: hard coatings, vapour phase lubrication and boundary film lubrication.…”

“…Redundancy with rewiring L3 [138] Critical function observed in the lab Surface lubrication L1 [139] Basic principles observed being polymorphic because of their ability to change their shape and move in various ways. S-bots are individual identical mobile robots which collectively compose a Swarm-bot [145].…”

Effects of Nanoscale Surface Texturing on Self-Healing of Boundary Lubricant Film via Lateral Flow

“…Most microelectromechanical systems (MEMS) are made of silicon-based materials through lithographic techniques. Silicon surfaces covered with native oxide can be lubricated and protected with cationic polymer lubricant (CPL) [2,3]. CPL is a lubricant that can form a bound-and-mobile phase that has self-healing capabilities.…”

“…CPL is a lubricant that can form a bound-and-mobile phase that has self-healing capabilities. CPL is a low molecular weight (1,800 g/mol) polydimethylsiloxane (PDMS) with quaternary ammonium iodide cationic groups covalently attached to the PDMS backbone [2,3]. CPL can form an electrostatically bound layer on SiO 2 surfaces that allows wear resistance and a multilayer which is mobile and can flow laterally into the lubricant-depleted area for self-healing.…”