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
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 TT 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