Nano-Liquids, Nano-Particles, Nano-Wetting: X-ray Scattering Studies Physics of Confined Liquids with/without Nanoparticles:  Confinement  Phase transitions are suppressed and/or shifted.  When do Liquids fill nano-pores? (i.e. wetting and capillary filling).  Contact Angles vary with surface structure. (i.e. roughness & wetting)  Attraction/repulsion between surfaces. (i.e. dispersions or aggregation)  Important for formation of Nanoparticle arrays: (i.e. electronic/optical properties, potential use for sensors, catalysis, nanowires) How will these affect nano-scale liquid devices? How will these affect processes that are essential for nano-scale liquid technology? P.S. Pershan: Physics & DEAS, Harvard Univ.

Co Workers Harvard Students and Post Docs K AlvineGraduate Student PhD March 06, Current: NIST D. PontoniPost Doc. O. GangFormer Post Doc.Current: Brookhaven National Lab. O. ShpykroFormer Grad. Student & Post Doc.Current: Argonne National Lab M. FukutoFormer Grad. Student & Post Doc.Current: Brookhaven National Lab Y. YanoFormer Guest.Current: Gakushuin Univ., Japan Others B. OckoBrookhaven National Lab. D. CooksonArgonne National Lab. A. CheccoBrookhaven National Lab. F. StellacciMIT K. ShinU. Mass. Amherst T. RussellU. Mass. Amherst C. BlackI.B.M.

Experiments: Thin to Thick Liquids Thin liquids adsorb on nano-structured surface Thin liquids surround and solvate nano-particles Liquids fill nano-pores

Control of Liquid 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:   C Vapor Pressure  Thickness  P   ~  T  Van der Waals Nano Thin Films

Van der Waals 1/3 Power Law Molecule to Surface: Molecule-Molecule:

X-Ray Reflectivity: Film Thickness

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

Capillary Filling of Nano-Pores (Alumina)  or  T Capillary Filling: Transition Energy Cost of Liquid Surface  Min: D  R 0 Volume  Min: D  0

Anodized Alumina (UMA) Fig. 1: AFM image (courtesy UMA) of anodized alumina sample. The ~15nm pores are arranged in a hcp array with inter-pore distance ~66nm Fig 2: SEM (courtesy of UMA) showing hcp ordering of pores and cross-section showing large aspect ratio and very parallel pores. ~90 microns thick Top Side ~ 15nm

SAXS Data Pore fills with liquid  Contrast Decreases Short Range Hexagonal Packing ∆T decreasing Thin films Condensation

Capillary filling—film thickness Wall film thickness [nm] ~ 2  /D Transition Liquid Layer ~ 1nm Pore Diameter~15nm What is the filling process?

Geometry: Theoretical Background C. Rascon and A. O. Parry, "Geometry-dominated fluid adsorption on sculpted solid substrates",Nature 407, 986 (2000).   Liquid Filling of Troughs

Parabolic Pits  =2)  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

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:

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

Results for Sculpted Surface R-P Prediction  c ~3.4  c  Observed  c  Sculpted Crossover to Flat Flat Sample Sculpted is Thinner than Flat

Gold Nanoparticles & Controlled Solvation Conventional Approach: Dry Bulk Solution  Imaging of Dry Sample Controlled Wetting: Dry Monolayer  Adsorption (Wetting Liquid) Langmuir Isotherms Formation Liftoff Area Of Monolayer

Thiol Coated Au Particles Stellacci et al OT: MPA (2:1) OT=CH 3 (CH 2 ) 7 SH MPA=HOOC(CH 2 ) 2 SH TEM bi-modal distribution Size Segregation

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

Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vapor Good Solvent Poor vs Good Solvent Reversible Aggregation in Poor Solvent Dissolution in Good Solvent Self Assembly Reversible Self Assembly: Annealing

NanoParticle SelfAssembly in Nanopores: Tubes Empty SEM of empty pores, diameter~30nm 50 nm Fill with Particles ~2nm dia. Filled TEM of nanoparticles in pores.

SAXS Experimental Setup Brief experiment overview: Study in-situ SAXS/WAXS of particle self assembly as function of added solvent. Solvent added/removed in controlled way via thermal offset as in flat case. Scattered x-rays TT Incident x-ray's Toluene Alumina membrane With nano-particles Small Q x : Pore-Pore Distances Large Q x, Q y.Q z : Particle-Particle Distances Top

Heating/Cooling, w/ nanoparticles Hex. Packing Small Q peaks pore filling hysteresis With nanoparticles Decrease/Increase in contrast indicates pores filling/emptying. Below: w/o nanoparticles Capillary transition shifts from ~2K for pores w/o nanoparticles to about ~8K w/ nanoparticles Strong hysteresis  T~  /R Note: Shift in Capillary Condensation

Summary of Au-Au Scattering(Drying) Real space model Slices q radial Intensity q radial Intensity q radial Images Intensity Cylind. Shell Shell + Isotropic clusters Shell + Isotropic solution Heating

Summary Control Thickness:  T~  X-ray: Non-destructive probe Capillary Filling: pores & structures Thin Liquid Solvation