nano-liquids, nano-particles, nano-wetting: x-ray scattering studies physics of confined liquids...
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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 DocsK Alvine Graduate Student PhD March 06, Current: NIST 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.
Experiments: Thin to Thick LiquidsThin 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 = Trsv.
Wetting film on Si(100) at T = Trsv + T.
Outer cell: 0.03CInner cell: 0.001C
T ~δ ~D−3
Vapor Pressure Thickness
δδP ~ T
Van der Waals
Nano Thin Films
Van der Waals 1/3 Power Law
Molecule to Surface: V (z) ~ d3r
r2 Arr1 −
rr2
6⎡⎣⎢
⎤⎦⎥~A z3∫
Molecule-Molecule: V (
rr1 −
rr2 ) ~A
rr−
rr2
6
r1
r2
z
X-Ray Reflectivity: Film Thickness
Qz = 4π λ( )sinα
€
Φ(Qz )2
~ A2 + B2 + 2AB cos QzD[ ]
R(Qz ) =RF (Qz) Φ(Qz)
2exp −Qz
2σeff2
( )
exp[−Qz
2σeff2 ]
Example of 1/3 Power Law
Methyl cyclohexane (MC) on Si at 46 °C
T [K]
Thi
ckne
ss L
[Å
]
L (2Weff /)1/3 (T)1/3
[J/cm3]
• 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
Capillary Filling of Nano-Pores (Alumina)
or TCapillary Filling:
Transition
Energy Cost of Liquid
2πγ R0 −D⎡⎣ ⎤⎦Surface
Min: DR0
π R0
2 − R0 −D( )2⎡
⎣⎢⎤⎦⎥
Volume
Min: D0
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
<10>
<11> <20>
Short Range Hexagonal Packing
∆T decreasing
Thin films
Condensation
Capillary filling—film thickness
Wal
l film
thi
ckne
ss [
nm]
~ 2γ/D
TransitionLiquid Layer ~ 1nm
Pore Diameter~15nm
What is the filling process?
Geometry: Theoretical BackgroundC. Rascon and A. O. Parry, "Geometry-dominated fluid adsorption on
sculpted solid substrates",Nature 407, 986 (2000).
y =L(x / x0 )
γ
γ 2 γ 2
Liquid Filling of Troughs
Parabolic Pits γ=2) Tom Russell (UMA)
Diblock Copolymer in Solvent
Self Alignment on Si
PMMA removal by UV degradation &
Chemical Rinse
Reactive Ion EtchingC. Black (IBM)
~40 nm Spacing
~20 nm Depth/Diameter
Height ~ r2
γ ≈2
X-ray Grazing Incidence Diffraction (GID) In-plane surface structure
Diffraction Pattern of Dry PitsHexagonal Packing
Thickness D~3 Cross over to other filling!
Liquid Fills Pore: Scattering Decreases:
Results for Sculpted Surface
Γc ~ T( )
−βc
R-P Predictionβc~3.4
βc 3
Observedβc 06
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)
LangmuirIsotherms
Formation
Liftoff AreaOf Monolayer
Thiol Coated Au Particles Stellacci et al OT: MPA (2:1)OT=CH3(CH2)7SHMPA=HOOC(CH2)2SH
TEMbi-modal distribution
Size Segregation
Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vapor
Good SolventPoor vs Good Solvent
Rev
ersi
ble
Aggregation in Poor Solvent
Dissolution in GoodSolvent
Self Assembly
(1) dry
(2) ethanol T ~ K
3 ethαnoλ T ~ 5 K
4 δy αγαin etOH extαcteδ
5 toλuene T 5 K
6 toλuene T ~ 5 K
toλuene T ~ 3 K
Reversible Self Assembly: Annealing
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
NanoParticle SelfAssembly in Nanopores: Tubes
Empty
SEM of empty pores, diameter~30nm
50 nm
Fill with Particles ~2nm dia.
FilledTEM 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
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
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
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