1. Wetting When It Isn’t Simple! P.S. Pershan, Harvard Univ. Simple Wetting Van der Waals (T>T boiling ) D

2. 1) Casimir Effect: Critical Binary Liquid Fisher and de Gennes (1978), Krech and Dietrich (1991, 1992) Correlation Length: Three Different Experiments D M. Fukuto,Y. Yana

3. 2) Structured Surface C. Rascon and A. O. Parry, Nature 407, 986 (2000).   O. Gang, B.Ocko,, K.Alvine, T. Russell,M. Fukuto, C. Black

4. 3) Reconstructing Surface Nanoparticles & Controlled Solvation Thiol Stabilized Au Particles (~ 2 to 8 nm) Dry Monolayer  Adsorption (Wetting Liquid) D. Pontoni, K. Alvine, A. Checco, O. Gang, B. Ockio, F. Stellacci

5. Control of Film Thickness Saturated vapor Bulk liquid reservoir: at T = T rsv. Wetting film on Si(100) at T = T rsv +  T . Outer cell:  0.03  C Inner cell:  0.001  C Vapor Pressure  Thickness  P   ~  T  Van der Waals Delicate Control:

6. X-Ray Reflectivity: Film Thickness

7. Example of 1/3 Power Law Methyl cyclohexane (MC) on Si at 46 °C  T  [K] Thickness L [Å] L  (2W eff /  ) 1/3  (  T  )  1/3  [J/cm 3 ] Via temperature offset  Comparisons Via gravity  For h < 100 mm,  < 10  5 J/cm 3  L > ~500 Å  small , large L Via pressure under-saturation  For  P/P sat > 1%,  > 0.2 J/cm 3 L < 20 Å  large , small L

8. Critical Casimir Effect in NanoThick Liquids: Binary Liquid 47.7 °C 46.2 °C 45.6 °C [Heady & Cahn, J. Chem. Phys. 58, 896 (1973)] T c = 46.13  0.01 °C, x c = 0.361  0.002 Methylcyclohexane (MC) Perfluoro- methylcyclohexane (PFMC) Fisher and de Gennes (1978), Krech and Dietrich (1991, 1992) x (PFMC mole fraction) Temperature [  C] PFMC rich MC rich

9. Thermodynamics Bulk MC + PFMC reservoir: ( x ~ x c = 0.36 ) at T = T rsv. wetting film on Si(100) T = T rsv +  T . Outer cell:  0.03  C Inner cell:  0.001  C Same Experiment: Thickness of Absorbed Film T=(T-T c )/T c  Film -T Res 2 Phase Coexistence Vapor Phase Liquid Phase Critical Point Experimental Paths Experimental Paths

10. q z [Å  1 ] R/RFR/RF X-ray reflectivity & Film thickness D Paths T film [°C] Film thickness L [Å] 0.50 K 0.10 K 0.020 K x = 0.36 ~ x c T c = 46.2 °C TT D vs........ T- T c

11. Theory Excess free energy/area of a wetting film:  Casimir term “Force” or “pressure” balance: y = (L/   ) 1/ = t (L/  0 + ) 1/  +,  (y) (+,  )  +,  (y) /  +,  (0) (+,  ) (+, +) d = 4 Ising (mean field) [M. Krech, PRE 1997] d = 2 Ising (exact) [R. Evans & J. Stecki, PRB 1994]

12. Experiment vs. Theory y = (L/   ) 1/ = t (L/  0 + ) 1/  T  0.020 K 0.10 K d = 2 (exact) d = 4 (MFT)  +,  (y)  +,  (0) Theory for y-dependence in d=3 does not exist! There is prediction for    for 3D.

13. Universal “Casimir amplitudes” At bulk T c (t = 0), scaling functions reduce to: For d = 3 Ising systems     Renormalization Group (RG) Monte Carlo [M. Krech, PRE 1997] -0.326 -0.345 2.39 2.450 “Local free energy functional” theory (LFEF) [Z. Borjan & P. J. Upton, PRL 1998] -0.423.1 Our Result N/A3 ± 1 For recent experiments with superfluid He (XY systems), see: R. Garcia & M.H.W. Chan, PRL 1999, 2002; T. Ueno et al., PRL 2003    (0) =  (0)/(d – 1)

14. Adsorption vs..... Shape: Phase Diagram 1/  Sculpted Surfaces Theory: Rascon & Parry, Nature (2000) Variety of Shapes (  Long Channels Planar Crossover Geometry to Planar Geometry Dominated Adsorbed Liquid ∞

15. Parabolic Pits: Tom Russell (UMA) Diblock Copolymer in Solvent Self Alignment on Si PMMA removal by UV degradation & Chemical Rinse Reactive Ion Etching C. Black (IBM) ~40 nm Spacing ~20 nm Depth/Diameter

16. X-ray Grazing Incidence Diffraction (GID)  In-plane surface structure Diffraction Pattern of Dry Pits Hexagonal Packing Thickness D~   Cross over to other filling! Liquid Fills Pore: Scattering Decreases:

17. X-ray Measurement of Filling GID Electron Density vs.....  T Filling Reflectivity Filling

18. Results for Sculpted Surface R-P Prediction  c ~3.4  c  Uncertainties? Flat Sample Sculpted is Thinner than Flat

19. Tasinkevych & Dietrich Volume of Liquid Filling Pores:  p Volume of Liquid above Pores:  t Film only coats Flat Part Area_Flat/Area Total:

20. Reconstructing Surface: Gold Nanoparticles & Controlled Solvation Controlled Wetting: Dry Monolayer  Adsorption Langmuir Isotherms Formation Liftoff Area Of Monolayer Stellacci et al (MIT) OT: MPA (2:1) OT=CH 3 (CH 2 ) 7 SH MPA=HOOC(CH 2 ) 2 SH Bimodal Size Distribution of Particles

21. GID: X-ray vs. Liquid Adsorption (small particles) GID Adsorption Return to Dry QzQz Q xy

22. Three FeaturesThat Can Be Understood! Solid lines are just guides for the eye! Temperature Dependence of Reflectivity: 1-Minimum at low q z 2-Principal Peak Reduces and Shifts 3-2nd Minima Moves to Lower q z

23. Construction of Model: Dry Sample Core size distribution Vertical electron density profile Model Fit: Based on Particle Size Distribution

24. Fits of Physical Model 1-Minimum at low q z 2-Principal Peak Reduces and Shifts 3-Second Minima Moves to Lower q z

25. Evolution of Model with Adsorption Thin wetting film regime Beginning of bilayer transition Thick wetting film regime

26. Bimodal Au nanocrystals in equilibrium with undersaturated vapor Good Solvent Poor vs..... Good Solvent Reversible Aggregation in Poor Solvent Dissolution in Good Solvent Self Assembly Summary of Nano-particle experiments

27. Summary Delicate Control of Wetting:  Wetting of Critical Liquid (Casimir) M. Fukuto,Y. Yana Wetting of Structured Surface (Rascon/Parry & Tasikevych/Dietrich) O. Gang, B.Ocko,, K.Alvine, T. Russell,M. Fukuto, C. Black Nano-Particles: Self Assembly D. Pontoni, K. Alvine, A. Checco, O. Gang, B. Ockio, F. Stellacci