Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems
| Autor: | René M. Overney, Tomoko Gray, Daniel B. Knorr |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Time Factors
Friction Surface Properties General Physics and Astronomy Thermodynamics Activation energy Reaction rate symbols.namesake chemistry.chemical_compound Pressure Physical and Theoretical Chemistry Arrhenius equation Chemistry Temperature Reproducibility of Results Dissipation Amorphous solid Kinetics Models Chemical Free surface symbols Polystyrenes Glass Polystyrene Glass transition |
| Zdroj: | The Journal of Chemical Physics. 129:074504 |
| ISSN: | 1089-7690 0021-9606 |
| DOI: | 10.1063/1.2968548 |
| Popis: | Energy dissipation in single asperity sliding friction was directly linked to submolecular modes of mobility by intrinsic friction analysis, involving time-temperature superposition along with thermodynamic stress and reaction rate models. Thereby, polystyrene served as a representative tribological sample for organic and amorphous complex systems. This study reveals the significance of surface and subsurface (alpha-, beta-, and gamma-) relaxational modes, which couple under appropriate external conditions (load, temperature, and rate) with shear induced disturbances, and thus gives rise to material specific frictional dissipation. At low pressures and temperatures below the glass transition point, the phenyl pendant side groups of polystyrene, known for their preferential orientation at the free surface, were noticed to be the primary channel for dissipation of kinetic sliding-energy. While this process was found to be truly enthalpic (activation energy of 8 kcalmol), energy dissipation was shown to possess both enthalpic and cooperative entropic contributions above the loading capacity of the surface phenyl groups (9.9 kcalmol) or above the glass transition. Apparent Arrhenius activation energies of frictional dissipation of 22 and 90 kcalmol, respectively, and cooperative contributions up to 80% were found. As such, this study highlights issues critical to organic lubricant design, i.e., the intrinsic enthalpic activation barriers of mobile linker groups, the evaluation of cooperative mobility phenomena, and critical tribological parameters to access or avoid coupling between shear disturbances and molecular actuators. |
| Databáze: | OpenAIRE |
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