(366e) Ionic Polymer Lubricants for Boundary Lubrication with Self-Healing Capability

As the size of mechanical devices now varies from the macroscale to the nanoscale, more innovative methods are needed to minimize wear caused by adhesion and friction on all scales. Among various coatings applied for this purpose, organic boundary lubrication films is one of the most widely studied and promising approach. However, one big challenge in this case is the lack of self-healing capability of the organic bound films, which limits the durability of the film. In order to overcome this challenge, it is required to synthesize a molecule that can be bound to the surface but still mobile on the surface. For this purpose, we synthesized ionic polymer lubricants (IPLs) by attaching ionic side chains to low molecular weight polydimethylsiloxane (PDMS) backbones. The basic idea is to combine the chemical reactivity of ionic liquids and lubricity of PDMS into one molecule. Thus, IPLs have ionic interactions with the substrates which will provide moderate binding needed for formation of the boundary lubrication layer. They also have a very flexible PDMS backbone that will allow lateral mobility and thus self-healing. Thus they can heal the bare surface exposed by removal of the boundary lubrication molecules via lateral diffusion from surrounding regions. Three cationic IPLs with varying amount of quaternary amine functional groups were synthesized and tested for nano-scale as well as macro-scale lubrication effects of silicon oxide surfaces using atomic force microscopy, scanning polarization force microscopy, pin-on-disc tribometer, and other spectroscopic analysis techniques. The effects of ionic groups in boundary lubrication properties will be discussed.