Kinetics and Energetics in Nanolubrication
Lubrication, one of human kind's oldest engineering disciplines, in the 19th century gained from Reynolds' classical hydrodynamic description a theoretical base unmatched by most of the theories developed in tribology to date. In the 20th century, however
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29. Kinetics and Energetics in Nanolubrication
What is inaccessible today may become accessible tomorrow as has happened by the invention of the microscope. . . . Coherent assumptions on what is still invisible may increase our understanding of the visi-
29.1 Background: From Bulk to Molecular Lubrication ........ 29.1.1 Hydrodynamic Lubrication and Relaxation ............................ 29.1.2 Boundary Lubrication ................... 29.1.3 Stick Slip and Collective Phenomena
885 885 885 885
29.2 Thermal Activation Model of Lubricated Friction............................ 887 29.3 Functional Behavior of Lubricated Friction............................ 888 29.4 Thermodynamical Models Based on Small and Nonconforming Contacts ... 890 29.5 Limitation of the Gaussian Statistics – The Fractal Space .................................. 891 29.6 Fractal Mobility in Reactive Lubrication .. 892 29.7 Metastable Lubricant Systems in Large Conforming Contacts ................ 894 29.8 Conclusion ........................................... 895 References .................................................. 895
framework based on an appropriate statistics. In tribology this is met with spectral descriptions of the dynamic sliding process. Statistical kernels are being developed for probability density functions to explain anomalous transport processes that involve long-range spatial or temporal correlations. With such theoretical developments founded in nanorheological experiments, a more realistic foundation will be laid to describe the behavior of lubricants in the confined geometries of the nanometer length scale.
ble. . . . Strong reasons have come to support a growing probability, and it can finally be said the certainty, in favor of the hypothesis of the atomists. (Jean Baptiste Perrin – Nobel Lecture, December 11, 1926)
Part D 29
Lubrication, one of human kind’s oldest engineering disciplines, in the 19th century gained from Reynolds’ classical hydrodynamic description a theoretical base unmatched by most of the theories developed in tribology to date. In the 20th century, however, increasing demands on lubricants shifted the attention from bulk film to ultrathin film lubrication. Finite size limitations imposed constraints on the lubrication process that were not considered in bulk phenomenological treatments introduced by Reynolds. At this point, as is common in many engineering applications, empiricism took over. Functional relationships derived from the classical theories were tweaked to accommodate the new situation of reduced scales by introducing “effective” or “apparent” properties. With the inception of nanorheological tools of complementary nature in the later decades of the 20th century (e.g., the surface forces apparatus and scanning force microscopy), tribology entered the realm of nanoscience. Through an increasing confidence in experimental findings on the nanoscale, kinetic and energetic theories incorporated interfacial and molecular constraints. The very fundamentals have been challenged in recent ye
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