Professor Seong H. Kim | Research
3. Self-healing boundary lubrication films
There is a need to develop efficient boundary lubrication films that can work without the replenishment from the vapor phase and be incorporated into the forthcoming MEMS technology. A new bound and mobile boundary lubricant, cationic polymer lubricant (CPL),∗ was synthesized for the protection of SiO2 and Si which are base materials for many MEMS devices. CPL forms an ionically bound layer and a mobile multilayer. The multilayer portion can easily flow into a region where CPL is worn off, leading to self-healing behavior. We test the lubrication and self-healing viability of CPL at nanoscale as well as macroscale.
In the macro-scale, the effects of ionic content, environmental condition, and advantage of the bound layer on self-healing demonstrates wear resistance and self-healing capability. CPL also mitigates the detrimental effects of humidity on the wear of SiO2. In the nano-scale, the results from disjoining pressure and viscosity measurements give insight into the lateral spreading of the mobile layer. The multilayer spreading rates were estimated to be ∼10-11 m2/s.
Mobile component of CPL multilayer after scratching the center with an AFM probe at very high contact pressures ∼5 Gpa. Instead of removing the CPL from the silicon, the CPL multilayer spread around the contacted region.
- ∗ E. Hsiao, D. Kim, and S. H. Kim "Effects of ionic side groups attached to polydimethylsiloxanes on lubrication of silicon oxide surfaces" Langmuir, 2009, 25, 9814-9823.