CATIONIC POLYMER LUBRICANT (CPL): A NEW BOUND AND MOBILE BOUNDARY LUBRICANT WITH SELF-HEALING CAPABILITIES
Open Access
- Author:
- Hsiao Liao, Erik
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 13, 2011
- Committee Members:
- Seong Han Kim, Dissertation Advisor/Co-Advisor
Seong Han Kim, Committee Chair/Co-Chair
Themis Matsoukas, Committee Member
Joseph Manuel Perez Sr., Committee Member
Evangelos Manias, Committee Member - Keywords:
- Self-healing
Lubricant
Polymer
Tribology
AFM - Abstract:
- The boundary film formation and lubrication effects of low-molecular-weight silicone molecules with cationic side groups were studied. Poly-(N,N,N-trimethylamine-3-propylmethylsiloxane-co-dimethylsiloxane) iodide was synthesized and deposited on silicon oxide surfaces to form a bound-and-mobile lubricant film. The effects of the ionically bound layer and mobile multilayers were investigated. Both nano- and macro-scale tribological tests revealed superior lubrication performance of the silicon molecule with cationic side chains over the neutral silicon molecule (which was modeled with polydimethylsiloxane with the same molecule weight). The multilayer films exhibited characteristic topographic features due to ionic interactions within the polymeric film. In the macro-scale, the effects of ionic content, environmental condition, and advantage of the bound layer on self-healing will be discussed to demonstrate the wear resistance and self-healing capability. The multilayer spreading rates were estimated to be ~10^-11 m2/s. In the nano-scale, the results of disjoining pressure and viscosity measurements help understand the lateral spreading of the mobile layer and identify the mobile species. The mobile species are the reduced tertiary amine form of CPL. The hydrophobic but hygroscopic properties of CPL are also investigated with SFG and ATR-IR. The CPL-coated surfaces are hydrophobic which prevents the detrimental effects of humidity on wear of silicon. In addition, the hygroscopic nature of CPL allows humidity to be absorbed into the film, which enhances the self-healing capabilities. Finally, by texturing the silicon surface with nanowells, self-healing is enhanced when the nanowells are filled with CPL. The nanowells serve as CPL reservoirs that are readily available for self-healing within the wear track for faster cycle intervals. However, the nanowells deteriorate the self-healing from surrounding the contact region due to the refilling of the empty nanowells.