Influence of salt on the aqueous lubrication properties of end-grafted, ethylene glycol-based self-assembled monolayers.
We have investigated the influence of a high-concentration salt solution (1 M NaCl) on the aqueous lubrication properties of ethylene glycol-based molecules, namely, alpha-methoxy-omega-mercaptopoly(ethylene glycol) (MW 5000 Da) and alpha-methoxy-omega-mercaptoheptakis(ethylene glycol) (MW 356 Da), which have been end-grafted onto polycrystalline gold surfaces at high surface density. Macroscopic-scale, yet nondestructive, pin-on-disk tribometry experiments revealed that a high concentration of sodium chloride is deleterious to the aqueous lubricating properties of both films under low-sliding-speed conditions. This behavior was observed to be closely associated with the more collapsed conformation of surface-grafted poly(ethylene glycol) polymer chains in concentrated salt solutions, as confirmed by quartz-crystal microbalance measurements.
Heeb
Raphael
R
Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
Lee
Seunghwan
S
Venkataraman
Nagaiyanallur V
NV
Spencer
Nicholas D
ND