title: Molecular dissipation phenomena of nanoscopic friction in the heterogeneous relaxation regime of a glass former.
abstract: Nanoscale sliding friction involving a polystyrene melt near its glass transition temperature Tg (373 K) exhibited dissipation phenomena that provide insight into the underlying molecular relaxation processes. A dissipative length scale that shows significant parallelism with the size of cooperatively rearranging regions (CRRs) could be experimentally deduced from friction-velocity isotherms, combined with dielectric loss analysis. Upon cooling to approximately 10 K above Tg, the dissipation length Xd grew from a segmental scale of approximately 3 A to 2.1 nm, following a power-law relationship with the reduced temperature Xd approximately TR-phi. The resulting phi=1.89+/-0.08 is consistent with growth predictions for the length scale of CRRs in the heterogeneous regime of fragile glass formers. Deviations from the power-law behavior closer to Tg suggest that long-range processes, e.g., the normal mode or ultraslow Fischer modes, may couple with the alpha relaxation, leading to energy dissipation in domains of tens of nanometers.
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle, Washington 98195-1750, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Sills
authors.forename: Tomoko
authors.initials: T
authors.lastname: Gray
authors.forename: René M
authors.initials: RM
authors.lastname: Overney