Pershan, Weizmann, Jan. ’ 06 1 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?

Pershan, Weizmann, Jan. ’ 06 2 Applications of Nano-Liquids/Nano- Particles A. Terray, J. Oakey, and D. W. M. Marr, Science 296, 1841 (2002). Particle rotation by optical traps  Pump 3  m Silica in 6  m Channel Sawitowski, T., Y. Miquel, et al. (2001). "Optical properties of quasi one- dimensional chains of gold nanoparticles." Advanced Functional Materials 11(6): Nano Particle Structures

Pershan, Weizmann, Jan. ’ 06 3 Co Workers Harvard Students and Post Docs K AlvineGraduate Student PhD Expected Jan/Feb 06 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.

Pershan, Weizmann, Jan. ’ 06 4 Liquid Surfaces Traditional Tools and/or Techniques Contact Angle Ellipsometry Non-Linear Optics Quartz Microbalance Macroscopic Length Scale:  m Interpretation: Theory Absorption AFM Imaging 

Pershan, Weizmann, Jan. ’ 06 5 Noncontact AFM imaging of liquids A. Checco, O. Gang and B. Ocko (Brookhaven National Laboratory) lock-in  Deflection sensor sine-wave generator AFM piezo-scanner dither piezo A A A  R AA R = 270 kHz Q=500 A set <10nm van der Waals forces Powerful: surface topology Adsorbed Liquid Chemical Pattern

Pershan, Weizmann, Jan. ’ 06 6 AFM Visualization of Condensation of ethanol onto COOH nanostripes COOH AFM topography across the stripes  T>>0  T~0  T< Limited by size of probes.

Pershan, Weizmann, Jan. ’ 06 7 Wetting & Nano Thin Films Macroscopic Liquid/Solid: Contact Angle Non-wetting Wetting  Macroscopic Meniscus Vapor Pressure  Thickness  P Van der Waals Nano Thin Films

Pershan, Weizmann, Jan. ’ 06 8 Control of  Bulk liquid reservoir: at T = T rsv. Wetting film on Si(100) at T = T rsv +  T . z Outer cell:  0.03  C Saturated vapor Chemical potential  was controlled by offset  T  between substrate and liquid reservoir. Dominant contribution to  is from latent heats of pure materials: Inner cell:   C  [n(s° v – s° l )]  T .

Pershan, Weizmann, Jan. ’ 06 9 System I: Structure normal to the surface : X-Ray Reflectivity q z log R q c Reflectivity  el Density Profile q z log R el z  z

Pershan, Weizmann, Jan. ’ Example of 1/3 Power Law  T  [K]  [J/cm 3 ] Thickness L [Å] L  (2W eff /  ) 1/3  (  T  )  1/3 Methyl cyclohexane (MC) on Si at 46 °C 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

Pershan, Weizmann, Jan. ’ System II: Capillary Filling of Nano-Pores (Alumina) Energy Cost of Liquid  or  T Capillary Filling: Transition Surface  Min: D  R 0 Volume  Min: D  0

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ SAXS Data Pore fills with liquid  Contrast Decreases Short Range Hexagonal Packing ∆T decreasing Thin films Condensation

Pershan, Weizmann, Jan. ’ Capillary filling—film thickness Wall film thickness [nm] ~ 2  /D Transition

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

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ 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:

Pershan, Weizmann, Jan. ’ X-ray Measurement of Filling GID Electron Density vs  T Filling Reflectivity Filling

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

Pershan, Weizmann, Jan. ’ Gold Nanoparticles & Controlled Solvation Conventional Approach: Dry Bulk Solution  Imaging of Dry Sample Controlled Wetting: Dry Monolayer  Adsorption Langmuir Isotherms Formation Liftoff Area Of Monolayer

Pershan, Weizmann, Jan. ’ Au Particles: Coating 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

Pershan, Weizmann, Jan. ’ GID: X-ray vs Liquid Adsorption (small particles) GID Adsorption Return to Dry QzQz Q xy

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ Construction of Model: Dry Sample Core size distribution Vertical electron density profile Model Fit: Based on Particle Size Distribution

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

Pershan, Weizmann, Jan. ’ Evolution of Model with Adsorption Thin wetting film regime Beginning of bilayer transition Thick wetting film regime

Pershan, Weizmann, Jan. ’ 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 Summary of Nano-particle experiments

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

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ Larger Q Data / WAXS (Particle-Particle Scattering) Slices Images Intensity q radial ( spherical coord.) Intensity q radial Intensity q radial Thin film Filled pore 1 2 3

Pershan, Weizmann, Jan. ’ Modeling WAXS with Shell/Tile Model 1)Break shell up into ~flat tiles no correlation between tiles.  2) Powder average over all tiles of a given orientation. 3)Scattering from 2) is same from flat monolayer S(q) is 2D lorentzian ring F(q) is form factor for distribution of polydisperse spheres (Shulz) 4) Add up scattering from all tile orientations 

Pershan, Weizmann, Jan. ’ Shell model fits for thin films: fit slices simultaneously with 3 global parameters plus backgnd. Nanoparticle radius, polydispersivity from bulk meas. Fits in good agreement with data. Fitted Data High  T

Pershan, Weizmann, Jan. ’ 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

Pershan, Weizmann, Jan. ’ Summary nanoparticle self-assembly Strong dependence upon solvent: –Subtle confinement effect for aggregation in “poor” solvent –Most systems reversible upon adding/removing solvent Able to probe different geometries: –Flat  sheets –Pores  tubes –Some similarity, interesting differences Thermal offset method gives us precise control of self- assembly process while doing in-situ measurements.

Pershan, Weizmann, Jan. ’ Critical Casimir Effect in Nano-Thick Liquids Binary Liquid 47.7 °C 46.2 °C 45.6 °C [Heady & Cahn, J. Chem. Phys. 58, 896 (1973)] T c =  0.01 °C, x c =  x (PFMC mole fraction) Temperature [  C] PFMC rich MC rich Methylcyclohexane (MC) Perfluoro- methylcyclohexane (PFMC)

Pershan, Weizmann, Jan. ’ Thermodynamic Casimir effect in critical fluid films Fisher & de Gennes (1978): Confinement of critical fluctuations in a fluid produces “force” between bounding interfaces 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:   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

Pershan, Weizmann, Jan. ’ X-ray reflectivity  Film thickness L T film [°C] Film thickness L [Å] 0.50 K 0.10 K K x = 0.36 ~ x c T c = 46.2 °C TT q z [Å  1 ] R/RFR/RF Paths

Pershan, Weizmann, Jan. ’ 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]

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

Pershan, Weizmann, Jan. ’ 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] “Local free energy functional” theory (LFEF) [Z. Borjan & P. J. Upton, PRL 1998] 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)

Pershan, Weizmann, Jan. ’ Summary  Flat Surfaces: van der Waals  1/3 power law  Porous Alumina: Capillary filling  Sculpted Surfaces: Cross over behavior  Nano Particles: Flat Surface Self Assembly & Solvent Effects. Size Segregation.  Nano Particles: Porous Alumina- Reversible self assembly, dissolution within the pore. Capillary filling changed be presence of the particles  Casimir Effect.  Monodisperse Particle  Vary force/solvent effects (Casimir effects)  Variation in Self Assembly  Test Casimir effect for symmetric bc. Delicate Control of Thickness of Thin Liquid Layers  T) Future