(383g) Molecular Simulation Study of Nanoscale Friction between Phosphocholine Self-Assembled Monolayer Surfaces Immersed in Ionic Solution

Tribology in biosystems is currently a rapidly growing area. While significant advances in the study of bio-lubrication systems have been made over the last few decades, the lubrication mechanism for the ?water-based' system still remains poorly understood. It is crucial to have a fundamental understanding of friction and adhesion for many biological applications such as joint replacement and contact lenses. The study of the bio-lubrication mechanism is also of great importance for the intelligent design of bio-interfaces. One of the major properties of biological lubrication system is that the lubricant is often chemical attached to the surface, the interactions between surface and interfacial water plays an important role in lubrication process, as occurs at the cartilage surface of joints. To mimic this, phosphocholine terminated self-assembly monolayers (PC-SAMs) were studied as model system in this research. Molecular simulation provides a unique tool to separate the intermingling interactions, look directly at the interaction surfaces, analyze friction properties, and obtain the molecular level understanding of the bio-lubrication mechanism. In this study, two PC-SAM surfaces were immersed in water and all-atom molecular dynamics simulation was performed to study their shearing phenomena with our BIOSURF program. Two water bulks were placed on both sides of surfaces. The effect of the concentration of sodium chloride on both friction coefficient and fluidity of PC-SAM was studied. Effects of different ions and pore size were also investigated to find their relations to friction properties. High concentration of ions had strong screening effect on the electrostatic interaction in the system. The dynamics of ions on PC-SAM surfaces was also investigated. Simulation results showed that friction between PC-SAM surfaces was lower than that between polyethylene (PE) surfaces, which indicated that PC-based materials may serve as an excellent candidate to reduce friction between PE surfaces in artificial joints.