nano-liquids, nano-particles, nano-wetting: x-ray scattering studies

1

Pershan, Weizmann,

Jan.’06

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

StudiesPhysics 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?

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Pershan, Weizmann,

Jan.’06

Applications of Nano-Liquids/Nano-Particles

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

A. Terray, J. Oakey, and D. W. M. Marr, Science 296, 1841 (2002).

•Particle rotation by optical traps Pump

•3m Silica in 6m Channel

Sawitowski, T., Y. Miquel, et al. (2001). "Optical properties of quasi one-dimensional chains of gold nanoparticles." Advanced Functional Materials 11(6): 435-440.

Nano Particle Structures

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Pershan, Weizmann,

Jan.’06

Co Workers

Harvard Students and Post DocsK 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 LabM. Fukuto Former Grad. Student & Post Doc. Current: Brookhaven National LabY. Yano Former Guest. Current: Gakushuin Univ., Japan

OthersB. Ocko Brookhaven National Lab.D. Cookson Argonne National Lab.A. Checco Brookhaven National Lab.F. Stellacci MITK. Shin U. Mass. AmherstT. Russell U. Mass. AmherstC. Black I.B.M.

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Pershan, Weizmann,

Jan.’06

Liquid SurfacesTraditional Tools and/or

TechniquesContact AngleEllipsometry Non-Linear Optics

P(2ω) ~χsurf (2ω,ω)Ein(ω)Quartz

Microbalance

Macroscopic •Length Scale: m

•Interpretation: TheoryAbsorption

AFM Imaging

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Pershan, Weizmann,

Jan.’06

Noncontact AFM imaging of liquids A. Checco, O. Gang and B. Ocko (Brookhaven National Laboratory)

lock-in Deflectionsensor

sine-wave generator

AFMpiezo-scanner

dither piezoA

A

A

R

A

R = 270 kHzQ=500

Aset<10nmvan der Waals forces

Powerful: surface topology

Adsorbed Liquid

Chemical Pattern

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Pershan, Weizmann,

Jan.’06

AFM Visualization of Condensation of ethanol onto

COOH nanostripes 1 8 . 0 0 n m

0 . 0 0 n m

COOH

200 400 600 800 1000 12000

3

6

9

12

15

nm

nm200 400 600 800 1000 12000

3

6

9

12

15

nm

nm

AFM topography across the

stripes

300nm

T>>0

300nm

T~0

300nm

T<0

200 400 600 800 1000 12000

3

6

9

12

15

nm

nm

1 2 3

1

2

3

Limited by size of probes.

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Pershan, Weizmann,

Jan.’06

Wetting & Nano Thin Films

Macroscopic Liquid/Solid:

Contact Angle

Non-wetting Wetting

Macroscopic Meniscus

δ ~D−3

Vapor Pressure Thickness

δδP

Van der Waals

Nano Thin Films

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Pershan, Weizmann,

Jan.’06

Control of

Bulk liquid reservoir: at T = Trsv.

Wetting film on Si(100) at T = Trsv + T.z

Outer cell: 0.03C

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: 0.001C

[n(s°v – s°l)] T.

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Pershan, Weizmann,

Jan.’06

System I: Structure normal to the surface : X-Ray Reflectivity

qz

log R

qc

Reflectivity

el

Density Profile

qz

log Rel

z

z

Qz = 4π ( )sinα

€

Φ(Qz )2

~ A2 + B2 + 2AB cos QzD[ ]

R(Qz )=RF (Qz) Φ(Qz)

2exp −Qz

2σeff2

( )

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Pershan, Weizmann,

Jan.’06

Example of 1/3 Power Law

T [K]

[J/cm3]

Thi

ckne

ss L

[Å

] L (2Weff /)1/3 (T)1/3

Methyl cyclohexane (MC) on Si at 46 °C

• Via temperature offset

Comparisons

• Via gravity

For h < 100 mm,

< 105 J/cm3

L > ~500 Å

small , large L

• Via pressure under-saturation

For P/Psat > 1%,

> 0.2

J/cm3

L < 20 Å

large , small L

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Pershan, Weizmann,

Jan.’06

System II: Capillary Filling of Nano-Pores (Alumina)

Energy Cost of Liquid

or TCapillary Filling:

Transition

2πγ R −D⎡⎣ ⎤⎦Surface

Min: DR0

π R

2 − R −D( )2⎡

⎣⎢⎤⎦⎥

Volume

Min: D0

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Pershan, Weizmann,

Jan.’06

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

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Pershan, Weizmann,

Jan.’06

SAXS Data

Pore fills with liquid Contrast Decreases

<10>

<11> <20>

Short Range Hexagonal Packing

∆T decreasing

Thin films

Condensation

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Pershan, Weizmann,

Jan.’06

Capillary filling—film thickness

Wal

l film

thi

ckne

ss [

nm]

~ 2γ/D

Transition

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Pershan, Weizmann,

Jan.’06

Adsorpton vs Shape: Phase Diagram

1/γ

System III: Sculpted Surfaces

Theory: Rascon & Parry, Nature (2000)

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are needed to see this picture.

Variety of Shapes (γ

Long Channels

Planar CrossoverGeometry to Planar

GeometryDominated

Height =L

xL

⎛

⎝⎜⎞

⎠⎟

γ Adsorbed Liquid ∞

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Pershan, Weizmann,

Jan.’06

Parabolic Pits: Tom Russell (UMA)

Diblock Copolymer in

Solvent

Self Alignment on Si

PMMA removal by UV

degradation & Chemical RinseReactive Ion

EtchingC. Black (IBM)

~40 nm Spacing

~20 nm Depth/Diameter

Height ~ r2

γ ≈2

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Pershan, Weizmann,

Jan.’06

X-ray Grazing Incidence Diffraction (GID) In-plane surface structure

Diffraction Pattern of Dry PitsHexagonal Packing

Thickness D~3Cross over to other filling!

Liquid Fills Pore: Scattering Decreases:

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Pershan, Weizmann,

Jan.’06

X-ray Measurement of Filling

GID

Electron Density vs T

Filling

Reflectivity

Filling

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Pershan, Weizmann,

Jan.’06

Results for Sculpted Surface

Γc ~ T( )

−βc

R-P Predictionβc~3.4

βc3

Observedβc

Sculpted Crossover to

Flat

Flat Sample

Sculpted is Thinner than Flat

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Pershan, Weizmann,

Jan.’06

Gold Nanoparticles & Controlled Solvation

Conventional Approach:Dry Bulk Solution Imaging of Dry Sample

Controlled Wetting:Dry Monolayer Adsorption

LangmuirIsotherms

Formation

Liftoff AreaOf Monolayer

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Pershan, Weizmann,

Jan.’06

Au Particles: Coating Stellacci et al OT: MPA (2:1)OT=CH3(CH2)7SHMPA=HOOC(CH2)2SHTEM

bi-modal distribution

Size Segregation

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Pershan, Weizmann,

Jan.’06

GID: X-ray vs Liquid Adsorption

(small particles)

GIDAdsorpt

ion

Return to Dry

Qz

QxyQxy Qxy

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Pershan, Weizmann,

Jan.’06

Three FeaturesThat Can Be Understood!

Solid lines are just guides for the eye!

Temperature Dependence of Reflectivity:

1-Minimum at low qz

2-Principal Peak Reduces and Shifts

3-2nd Minima Moves to Lower qz

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Pershan, Weizmann,

Jan.’06

Construction of Model: Dry Sample

Core size distribution

Vertical electrondensity profile

Model Fit: Based on Particle Size Distribution

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Pershan, Weizmann,

Jan.’06

Fits of Physical Model

1-Minimum at low qz

2-Principal Peak Reduces and Shifts

3-Second Minima Moves to Lower qz

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Pershan, Weizmann,

Jan.’06

Evolution of Model with Adsorption

Thin wetting film regime

Beginning of bilayer transition

Thick wetting film regime

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Pershan, Weizmann,

Jan.’06

DRY

toluene T~3K

tolueneT~.5K

tolueneT~5mK

tolueneT~.5K

tolueneT~3K

Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vaporGood Solvent Poor vs Good Solvent

Rev

ersi

ble

Aggregation in Poor Solvent

Dissolution in GoodSolvent

Self Assembly

(1) dry

(2) ethanol T~K

(3)ethanolT~5mK

(4)dryagain(etOHextracted)

(5)tolueneT=5K

()tolueneT~5mK

()tolueneT~3K

Summary of Nano-particle experiments

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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Pershan, Weizmann,

Jan.’06

NanoParticle Assembly in Nanopores: Tubes

Empty

SEM of empty pores, diameter~30nm

50 nm

Fill with Particles ~2nm dia.

FilledTEM of nanoparticles in pores.

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Pershan, Weizmann,

Jan.’06

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

Incident x-ray's

Toluene

Alumina membraneWith nano-particles

Small Qx: Pore-Pore Distances

Large Qx, Qy.Qz: Particle-Particle Distances

z

x

Q

Qz

Qx

Top

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Pershan, Weizmann,

Jan.’06

Heating/Cooling, w/ nanoparticles

Hex. Packing

Small Q peaks pore filling hysteresis

<01>

<11>

<02>

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

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Pershan, Weizmann,

Jan.’06

Larger Q Data / WAXS (Particle-Particle Scattering)

SlicesImages

Inte

ns

ity

q radial (spherical coord.)

Inte

ns

ity

q radial In

ten

sit

y

q radial

Thin film

Filled pore

1

2

3

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Pershan, Weizmann,

Jan.’06

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

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Pershan, Weizmann,

Jan.’06

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

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Pershan, Weizmann,

Jan.’06

Summary of Au-Au Scattering(Drying)

Real space modelSlices

q radial

Inte

ns

ity

q radial

Inte

ns

ity

q radial

Images

Inte

ns

ity

Cylind.Shell

Shell + Isotropicclusters

Shell + Isotropicsolution

Heatin

g

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Pershan, Weizmann,

Jan.’06

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.

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Pershan, Weizmann,

Jan.’06

Critical Casimir Effect in Nano-Thick LiquidsBinary Liquid

47.7 °C

46.2 °C

45.6 °C

[Heady & Cahn, J. Chem. Phys. 58, 896 (1973)]

Tc = 46.13 0.01 °C, xc = 0.361 0.002

x (PFMC mole fraction)

Tem

pera

ture

[C

]PFMC rich

MC rich

Methylcyclohexane (MC)

Perfluoro-methylcyclohexane

(PFMC)

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Pershan, Weizmann,

Jan.’06

Thermodynamic Casimir effect in critical fluid filmsFisher & de Gennes (1978): Confinement of critical fluctuations in a fluid

produces “force” between bounding interfaces

Bulk MC + PFMC reservoir:(x ~ xc = 0.36) at T = Trsv.

wetting film on Si(100)

T = Trsv + T.

Outer cell: 0.03C

Inner cell: 0.001C

Same Experiment: Thickness of Absorbed Film

T=(T-Tc)/Tc

Film-TRes2 Phase

Coexistence

Vapor Phase

Liquid Phase

Critical Point

ExperimentalPaths

ExperimentalPaths

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Pershan, Weizmann,

Jan.’06

X-ray reflectivity Film thickness L

Tfilm [°C]

Film

thic

knes

s L

[Å

]

0.50 K

0.10 K

0.020 K

x = 0.36 ~ xc

Tc =

46.

2 °C

T

qz [Å1]

R/R

F

Paths

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Pershan, Weizmann,

Jan.’06

Theory

( ) ( )22 L

LTk

L

WLLF cBeff ξθ

μ ++Δ≈ΔExcess free energy/area of a wetting film:

Casimir term

( ) 3/12⎥⎦

⎤⎢⎣

⎡Δ

Θ+≈⇒

μ

ξLTkWL cBeff “Force” or “pressure” balance: 0=

∂∂−LF

y = (L/)1/ = t (L/0+)1/ 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]

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Pershan, Weizmann,

Jan.’06

Experiment vs Theory

y = (L/)1/ = t (L/0+)1/

T 0.020 K0.10 Kd = 2 (exact)

d = 4 (MFT)

+,(y)

+,(0)

Theory for d=3 does not exist!

There is prediction for for 3D.

41

Pershan, Weizmann,

Jan.’06

Universal “Casimir amplitudes”

• At bulk Tc (t = 0), scaling functions reduce to:

For d = 3 Ising systems

Renormalization Group (RG)Monte Carlo [M. Krech, PRE 1997]

-0.326-0.345

2.392.450

“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

(0) = (0)/(d – 1)

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Pershan, Weizmann,

Jan.’06

Summary

Flat Surfaces: van der Waals1/3 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