Abstract
The nanotribological properties of molecularly thin films of polymer melts were investigated using a surface forces apparatus (SFA). When the droplet of a polymer melt was injected between two smooth mica surfaces and confined by normal compression, the dynamic properties of the polymer melt shifted from bulk rheological to thin film tribological features. The shift of the dynamics was evaluated by measuring the effective viscosity of the confined films and by comparing the viscosity with its bulk value; the results were discussed in terms of confinement-induced glasslike transition. Molecular ordering (layering) in confined polymer melts was also studied. The tribological properties of the thin films of poly(dimethylsiloxane) (PDMS) were evaluated. The results implied well-ordered layer structures in the confined films, which are very different from most of the hydrocarbon-type polymeric lubricants (having disordered molecular conformations in confinement). The experiments described here reveal the unique dynamics of molecularly confined polymer melts, which cannot be obtained by any other experimental techniques than SFA.
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