Nano-Liquids, Nano-Particles, Nano-Wetting: X-ray Scattering Studies

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 fornano-scale liquid technology?
2
Applications of Nano-Liquids/Nano-Particles
3
Co Workers
Harvard Students and Post Docs K Alvine Graduate
Student PhD Expected Jan/Feb 06 D. Pontoni Post
Doc. O. Gang Former Post Doc. Current
Brookhaven National Lab. O. Shpykro Former Grad.
Student Post Doc. Current Argonne National
Lab M. Fukuto Former Grad. Student Post
Doc. Current Brookhaven National Lab Y.
Yano Former Guest. Current Gakushuin Univ.,
Japan Others B. Ocko Brookhaven National
Lab. D. Cookson Argonne National Lab. A.
Checco Brookhaven National Lab. F.
Stellacci MIT K. Shin U. Mass. Amherst T.
Russell U. Mass. Amherst C. Black I.B.M.
4
Liquid SurfacesTraditional Tools and/or
Techniques
AFM Imaging ?
5
Noncontact AFM imaging of liquids A. Checco, O.
Gang and B. Ocko (Brookhaven National Laboratory)
sine-wave generator
AFM piezo-scanner
A
lock-in
f
Deflection sensor
dither piezo
A
Adsorbed Liquid
van der Waals forces
Chemical Pattern
Powerful surface topology
6
AFM Visualization of Condensation of ethanol onto
COOH nanostripes
1
2
3
COOH
AFM topography across the stripes
3
2
1
Limited by size of probes.
7
Wetting Nano Thin Films
8
Control of ??
Outer cell ?0.03?C
Inner cell ?0.001?C
Wetting film on Si(100) at T Trsv DTm.
z
Saturated vapor
Bulk liquid reservoir at T Trsv.

• Chemical potential Dm was controlled by offset
  DTm between substrate and liquid reservoir.
• Dominant contribution to Dm is from latent heats
  of pure materials

Dm? n(sv sl) DTm.
9
System I Structure normal to the surface X-Ray
Reflectivity
10
Example of 1/3 Power Law
Methyl cyclohexane (MC) on Si at 46 C

• Via temperature offset

L ? (2Weff /Dm)1/3 ? (DTm)-1/3
Thickness L Å
DTm K
Dm J/cm3
11
System II Capillary Filling of Nano-Pores
(Alumina)
Energy Cost of Liquid
12
Anodized Alumina (UMA)
Top
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
15nm
Side
13
SAXS Data
Pore fills with liquid ?Contrast Decreases
14
Capillary fillingfilm thickness
Transition
15
System III Sculpted Surfaces
Theory Rascon Parry, Nature (2000)
Crossover Geometry to Planar
Planar
Geometry Dominated
16
Parabolic Pits Tom Russell (UMA)
Diblock Copolymer in Solvent
40 nm Spacing 20 nm Depth/Diameter
17
X-ray Grazing Incidence Diffraction (GID)
In-plane surface structure
Liquid Fills Pore Scattering Decreases
18
X-ray Measurement of Filling
19
Results for Sculpted Surface
Sculpted is Thinner than Flat
Flat Sample
?c?????
Observed ?c??????
20
Gold Nanoparticles Controlled Solvation
Liftoff Area Of Monolayer
21
Au Particles Coating
Stellacci et al OT MPA (21)OTCH3(CH2)7SHMP
AHOOC(CH2)2SH
Size Segregation
22
GID X-ray vs Liquid Adsorption(small particles)
Return to Dry
23
Temperature Dependence of Reflectivity
24
Construction of Model Dry Sample
Model Fit Based on Particle Size Distribution
Vertical electron density profile
Core size distribution
25
Fits of Physical Model
26
Evolution of Model with Adsorption
27
Summary of Nano-particle experiments
Bimodal/polydisperse Au nanocrystals in
equilibrium with undersaturated vapor
Poor vs Good Solvent
Good Solvent
Aggregation in Poor Solvent
Reversible
Dissolution in Good Solvent
Self Assembly
28
NanoParticle Assembly in Nanopores Tubes

29
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.

Small Qx Pore-Pore Distances Large Qx, Qy.Qz
Particle-Particle Distances
30
Small Q peaks pore filling hysteresis
lt01gt
lt11gt
lt02gt

• Decrease/Increase in contrast indicates pores
  filling/emptying.

31
Larger Q Data / WAXS (Particle-Particle
Scattering)
32
Modeling WAXS with Shell/Tile Model
?
2) Powder average over all tiles of a given
orientation.

1. Break shell up into flat tiles no correlation
   between tiles.

• 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 ?

33
Fitted Data
High ?T

• 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.

34
Summary of Au-Au Scattering(Drying)
Real space model
Images
Slices
Cylind. Shell
Intensity
q radial
Shell Isotropic clusters
Intensity
Heating
q radial
Shell Isotropic solution
Intensity
q radial
35
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.

36
Critical Casimir Effect in Nano-Thick
LiquidsBinary Liquid
Methylcyclohexane (MC)
Perfluoro- methylcyclohexane (PFMC)
Heady Cahn, J. Chem. Phys. 58, 896 (1973) Tc
46.13 ? 0.01 C, xc 0.361 ? 0.002
37
Thermodynamic Casimir effect in critical fluid
filmsFisher de Gennes (1978) Confinement of
critical fluctuations in a fluid produces
force between bounding interfaces
Same Experiment Thickness of Absorbed Film
Critical Point
38
X-ray reflectivity ? Film thickness L
Paths
39
Theory
40
Experiment vs Theory
There is prediction for ????????for 3D.
Theory for d3 does not exist!
41
Universal Casimir amplitudes
At bulk Tc (t 0), scaling functions reduce to
D ? q(0) Q(0)/(d 1)
For d 3 Ising systems D, D,-
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 -0.42 3.1
Our Result N/A 3 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
42
Summary
Delicate Control of Thickness of Thin Liquid
Layers (???T)

• 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.

Future

• Monodisperse Particle
• Vary force/solvent effects (Casimir effects)
• Variation in Self Assembly
• Test Casimir effect for symmetric bc.