Abstract
The friction properties of the molecularly thin films of a poly (dimethylsiloxane) (PDMS) melt (Mw ≈ 80000) were investigated using the surface forces apparatus (SFA). When a PDMS droplet was confined between mica surfaces by normal compression, PDMS molecules were squeezed out from between the surfaces and formed a confined hard-wall film. The measurements of the dynamic thickness and friction reveal that PDMS molecules form well-ordered layer structures in the hard-wall film, and the friction mechanisms involve the slippage between ordered PDMS layers. The film structures and resulting friction properties observed for confined PDMS are very different from those of most of the hydrocarbon-type polymeric lubricants, which generally have disordered film structures in confinement and exhibit rheological responses upon shearing. The SFA enables us to clarify the unique friction mechanisms of a confined PDMS melt at the molecular scale, which must be also useful to understand the macroscopic tribological phenomena on PDMS lubricated surfaces.
