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Exploring Nanofriction: The Science Behind Microscopic Friction Mechanisms

Dive into the world of nanofriction with a comprehensive overview of experimental methods, theoretical models, and simulation techniques. Understand the complexities of friction at the nanoscale and its relevance in nanotechnology. Learn about key historical figures and modern research in the field.

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Exploring Nanofriction: The Science Behind Microscopic Friction Mechanisms

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  1. NANOFRICTION-- AN INTRODUCTION E. Tosatti SISSA/ICTP/Democritos TRIESTE

  2. Contents 1. Friction. Generalities, history. 2. “Stick-slip” versus smooth sliding; friction mechanisms. 3. Nanofriction: experimental methods. AFM, QCM, SFA… 4. Nanofriction: theory . a). Linear response b). Nonlinear friction in simple models: Prandtl-Tomlinson, Frenkel-Kontorova c). Simulated nanofriction: Molecular Dynamics--applications

  3. FRICTION NANOFRICTION FN FL (MEYER) (BRAUN) FRICTION COEFFICIENT: m = FL/ FN (usually~0.1-1) General Refs: B.N.J. PERSSON, Sliding Friction, Springer (2000); J.KRIM, Surf. Sci. 500, 741 (2002)

  4. RELEVANCE -- FRICTION: energy conservation; machine wear; ... -- NANOFRICTION: basic understanding; nanotechnology.

  5. HISTORY LEONARDO DA VINCI 1. Friction is independent of the geometrical contact area 2. Friction is proportional to normal load AMONTONS Guillaume Amontons (1663-1705)

  6. COULOMB 3. Friction independent of velocity 4. Friction tied to roughness EULER 5. Static vs. dynamic friction

  7. STATIC vs DYNAMIC FRICTION SLIDING VELOCITY Fs= Fd Fk= Fr APPLIED FORCE

  8. WHY FRICTION IS INDEP. OF AREA, AND PROPORT. TO LOAD Philip Bowden 1903-1968 Real contact surface AR= FN/s << A DaVinci-Amonton's law explained: FL = t AR = t FN /s = m FN yield stress BOWDEN - TABOR, 1950s David Tabor 1913-2005

  9. Rodrigues et al. (2000) Au NANOCONTACTS

  10. MORE GENERAL SLIDING FRICTION MECHANISMS -- Entanglement of asperities, plastic deformation, wear (commonest macroscopic friction mechanism) -- Viscous friction (fluid interfaces, acquaplaning) -- Phonon dissipation, elastic deformation (flat solid interfaces) -- Bulk viscoelastic dissipation (e.g., car tyres) -- Electronic friction (metals, still being established) -- Vacuum friction (more speculative) -- .....

  11. 6. Stick-slip motion vs smooth sliding low velocity &/or soft system high velocity &/or stiff system

  12. SOME EXPERIMENTAL NANOFRICTION METHODS

  13. SOME EXPERIMENTAL TECHNIQUES MACRO-MESOSCOPIC NANO Tabor, Winterton, Israelachvili (~1975) Binnig, Quate, Gerber (1986)

  14. FRICTION NANOFRICTION (MEYER) GERD BINNIG HEINI ROHRER

  15. AFM INSTRUMENTS Measure FL , F N Typical F N1-100 nN (MEYER)

  16. NaCl(100) (MEYER et al) -- “ATOMIC” STICK-SLIP MOTION OF TIP -- ENCLOSED AREA IN (F, x) PLANE EQUALS DISSIPATED FRICTIONAL ENERGY

  17. QCM (QUARTZ CRYSTAL MICROBALANCE) a Slip timet: 2 t: = d (Q-1)/dw KRIM, WIDOM, PRB 38, 12184 (1986)

  18. QCM Frequency n= 107 Hz Amplitude a = 100 Angstrom Velocity v ~ 2pna ~ 0.6m/s |Finertial|~ M (2pn)2 a = 3 x 10-15N ~3 x 10-6nN VERY WEAK FORCE --> LINEAR RESPONSE REGIME!

  19. THEORY (a) LINEAR RESPONSE

  20. ZERO EXTERNAL FORCE: 2D BROWNIAN DIFFUSION <r2> = 4 Dt y x

  21. WEAK EXTERNAL FORCE: 2D “DIFFUSIVE” DRIFT

  22. LINEAR RESPONSE THEORY < v > /m =F ---->> “viscous” friction m = mobility EINSTEIN RELATION m=D/ kBT D = S (w=0) S (w) = F.T. { <v(t) - v(0)>} VIVISCOUS FRICTION GOOD FOR FLUIDS, BUT NOT FOR SOLIDS: VIOLATES “OBEY” COULOMB’S LAW, F DEPENDENT ON VELOCITY

  23. THEORY (b) SIMPLE (“MINIMALISTIC” ) FRICTION AND NANOFRICTION MODELS

  24. PRANDTL-TOMLINSON MODEL (1928) v keff H= (E0/2)cos(2pxtip/a) + (keff/2)(xtip-x)2+damping

  25. STIFF SOFT LARGE K SMALL E LARGE E SMALL K SMOOTH SLIDING STICK-SLIP SLIDING F~ log v “COULOMB”! F~ v SASAKI, KOBAYASHI, TSUKADA, PRB 54 ,2138 (1996)

  26. STICK-SLIP

  27. FRENKEL-KONTOROVA MODEL (1938) K e O.M.BRAUN, YU.S.KIVSHAR, The Frenkel Kontorova Model: Concepts, Methods, Applications, Springer (2004)

  28. THE AUBRY TRANSITION INCOMMENSURATE: a c / a b = IRRATIONAL Fstatic SLIDING K e PINNED e g = K / gc gg g >gc ZERO STATIC FRICTION g <gc FINITE STATIC FRICTION (“PINNING”)

  29. PHONON GAP OF PINNED SLIDER w2 g > gc g < gc q q

  30. THEORY (c) NANOFRICTION SIMULATIONS -- NEWTONIAN or LANGEVIN DYNAMICS -- FROM MODELS TO REALISTIC MOLECULAR DYNAMICS (MD) -- MD: EMPIRICAL AND AB INITIO FORCES -- VARIETY OF SYSTEMS, APPLICATIONS

  31. MOLECULAR DYNAMICS SIMULATIONS NEWTON TOT (FREE) EN. LANGEVIN THERMAL NOISE + - gvi(t)+ hi(t)

  32. EMPIRICAL INTERPARTICLE FORCES (EXAMPLE: LENNARD-JONES PAIR POTENTIAL)

  33. SLAB GEOMETRY FREE SURFACE PBC PBC FREE SURFACE

  34. EXAMPLE: “GRAZING” FRICTION SIMULATION Diamond V NaCl

  35. Load = 1.0 nN T = 1100 K (6 Ang) Zykova-Timan, et al, Nature Materials6, 231 (2007)

  36. EXAMPLE: “PLOWING” FRICTION WITH WEAR HIGH TEMPERATURE NANOFRICTION, DIAMOND ON NaCl(100) Zykova-Timan, Ceresoli, Tosatti, Nature Materials6, 231 (2007)

  37. PLOWING FRICTION FORCES v = 50 m/s T=1100 K Normal force 6 Angstrom penetration

  38. HIGH T FRICTIONAL DROP: SKATING “SKATING” TIP IN LOCAL LIQUID CLOUD FURROW CLOSES UP BEHIND TIP v = 50 m/s

  39. SIMULATED LUBRICATION (BRAUN)

  40. SQUEEZOUT TARTAGLINO, SIVEBAEK, PERSSON, TOSATTI, J. Chem Phys 125, 014704 (2006)

  41. BRAUN, PRL (2006)

  42. WHERE DOES THE ENERGY GO? WEAR + PHONONS IN SIMULATION, THE THERMOSTATING METHOD MAY INFLUENCE AND FALSIFY THE REAL PHONON FRICTION Temp.(K) t (fs)

  43. SUMMARY FRICTION OFFERS MUCH MORE INTEREST AT NANOSCALE SIMPLE MODELS DEMONSTRATE STICK-SLIP, PINNING TRANSITION SIMULATIONS EXTREMELY USEFUL AND PREDICTIVE IN NANOFRICTION DISPOSAL OF DISSIPATED PHONON ENERGY NEEDS SPECIAL ATTENTION THE END

  44. SOME REFERENCES General : B.N.J. PERSSON, Sliding Friction, Springer (2000); J.KRIM, Surf. Sci. 500, 741 (2002) Stic-slip in Prandtl- Tomlinson Model:SASAKI, KOBAYASHI, TSUKADA, PRB 54 ,2138 (1996) Frenkel-Kontorova Model: O.M.BRAUN, YU.S.KIVSHAR, The Frenkel Kontorova Model: Concepts, Methods, Applications, Springer (2004) Nanofriction Simulation: Zykova-Timan et al, Nat. Materials6, 231 (2007) Squeezout Simulation: TARTAGLINO, SIVEBAEK, PERSSON, TOSATTI, J. Chem Phys 125, 014704 (2006) Nanoscale Rolling Simulation: O.M. BRAUN, PRL (2006)

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