Influence of molecular architecture on the adsorption of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) on PDMS surfaces and implications for aqueous lubrication

We have investigated the adsorption and lubrication properties of a series of poly(ethylene oxide)-poly(propylene oxide) -poly(ethylene oxide) (PEO-PPO-PEO) block copolymers ("Pluronic") to examine the feasibility of using them as aqueous lubricant additives. The adsorption behavior of PEO-PPO-PEO onto poly(dimethylsiloxane) (PDMS) surfaces was studied by optical waveguide lightmode spectroscopy (OWLS). The amount of adsorbed PEO-PPO-PEO copolymer exhibited a systematic variation, mainly according to the formula weight of the PPO block, and was found to increase with increasing PPO block size. The lubricating properties of the copolymers were investigated by means of pin-on-disk tribometry, employing self-mated PDMS as a tribo-pair in an aqueous environment. The lubricating behavior of the PEO-PPO-PEO copolymers was observed to be closely associated with their adsorption properties onto the PDMS surface; effective lubrication under low-velocity conditions was observed for those PEO-PPO-PEO copolymers that exhibited a significant adsorption of the PPO block, yet a significant role of the PEO block was also observed. The lubrication capabilities of PEO-PPO-PEO copolymers in aqueous media were attributed to the reduction of the hydrophobic interaction between PDMS surfaces by coating the surface with the copolymer and facilitating the formation of an aqueous lubricating film at the sliding interface.