Wetting When It Isn’t Simple! P.S. Pershan, Harvard Univ.
Download
Report
Transcript Wetting When It Isn’t Simple! P.S. Pershan, Harvard Univ.
Wetting When It Isn’t
Simple!
P.S. Pershan, Harvard Univ.
(T>Tboiling)
Simple Wetting
Bulk
Bulk
Liquid
(T ) Vapor
(T )
Van der Waals
Bulk
Bulk
Vapor
(T ) Liquid
(T ) VdW / D3
D
D ~
1/ 3
Three Different Experiments
•
1) Casimir Effect: Critical Binary Liquid
•
Fisher and de Gennes (1978), Krech and Dietrich (1991, 1992)
•
Correlation Length:
M. Fukuto,Y. Yana
D
~ 1 / T Tc
2) Structured Surface
C. Rascon and A. O. Parry, Nature 407, 986 (2000).
O. Gang, B.Ocko,, K.Alvine, T. Russell,M. Fukuto, C. Black
y L(x / x0 )
3) Reconstructing Surface
D. Pontoni, K. Alvine, A. Checco, O. Gang, B. Ockio, F. Stellacci
Nanoparticles & Controlled Solvation
Thiol Stabilized Au
Particles
(~ 2 to 8 nm)
Dry Monolayer Adsorption (Wetting Liquid)
Control of Film Thickness
Vapor Pressure Thickness
Delicate Control:
Outer cell: 0.03C
Inner cell: 0.001C
Wetting film on Si(100) at T
= Trsv + T.
Saturated
vapor
Bulk liquid reservoir:
at T = Trsv.
P ~ T
Van der Waals
T ~ ~ D 3
X-Ray Reflectivity: Film Thickness
Qz 4 sin
2
2
R(Qz ) RF (Qz ) (Qz ) exp Qz2 eff
2
(Qz ) ~ A 2 B 2 2AB cosQz D
2
exp[Qz2 eff
]
Example of 1/3 Power Law
Methyl cyclohexane (MC) on Si at 46 °C
Thickness L [Å]
• Via temperature offset
Comparisons
• Via gravity
For h < 100 mm,
< 105 J/cm3
L (2Weff /)1/3 (T)1/3
L > ~500 Å
small , large L
• Via pressure
under-saturation
For P/Psat > 1%,
T [K]
> 0.2 J/cm3
L < 20 Å
large , small L
[J/cm3]
Critical Casimir Effect in
NanoThick Liquids: Binary Liquid
Fisher and de Gennes (1978), Krech and Dietrich (1991, 1992)
Perfluoromethylcyclohexane
(PFMC)
Temperature [C]
Methylcyclohexane
(MC)
MC
rich
PFMC
rich
47.7 °C
46.2
°C
x (PFMC mole fraction)
[Heady & Cahn, J. Chem. Phys. 58, 896 (1973)]
Tc = 46.13 0.01 °C,
xc = 0.361 0.002
45.6
°C
Thermodynamics
Same Experiment: Thickness of Absorbed Film
T=(T-Tc)/Tc
Experimental
Paths
wetting film on Si(100)
T = Trsv + T.
Liquid Phase
Outer cell: 0.03C
Inner cell: 0.001C
Vapor Phase
Critical Point
Film-TRes
Bulk MC + PFMC reservoir:
(x ~ xc = 0.36) at T = Trsv.
2 Phase
Coexistence
X-ray reflectivity & Film thickness D
D vs........ TTc
x = 0.36 ~ x
Paths
R/RF
Tc = 46.2 °C
Film thickness L [Å]
c
T
0.020 K
0.10 K
0.50 K
qz [Å1]
Tfilm [°C]
Theory
Excess free energy/area
of a wetting film:
F L L
L2
F
0
L
k BTc L Casimir term
L2
2Weff k BTc L
L
1/ 3
d = 2 Ising (exact)
d = 4 Ising (mean field)
[R. Evans & J. Stecki, PRB 1994]
[M. Krech, PRE 1997]
(+,)
(+, +)
y = (L/)1/ = t (L/0+)1/
+,(y) / +,(0)
+,(y)
“Force” or “pressure” balance:
Weff
(+,)
(+, +)
y = (L/)1/ = t (L/0+)1/
Experiment vs. Theory
d = 4 (MFT)
There is prediction for
for 3D.
+,(y)
+,(0)
d = 2 (exact)
y = (L/)1/ = t (L/0+)1/
Theory for y-dependence in d=3 does not exist!
T
0.020 K
0.10 K
Universal “Casimir amplitudes”
• At bulk Tc (t = 0), scaling functions reduce to:
(0) = (0)/(d – 1)
For d = 3 Ising systems
Renormalization Group (RG)
Monte Carlo
-0.326
-0.345
2.39
2.450
-0.42
3.1
N/A
3±1
[M. Krech, PRE 1997]
“Local free energy functional” theory (LFEF)
[Z. Borjan & P. J. Upton, PRL 1998]
Our Result
For recent experiments with superfluid He (XY systems), see:
R. Garcia & M.H.W. Chan, PRL 1999, 2002; T. Ueno et al., PRL 2003
Sculpted Surfaces
Theory: Rascon & Parry, Nature (2000)
x
Long
Height L
Channels
L
Variety of Shapes (
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Geometry
Crossover
Planar
Adsorption vs.....
Shape: Phase
Dominated
Geometry to Planar
Diagram
1/
Adsorbed Liquid
∞
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
Height ~ r 2
~20 nm Depth/Diameter
2
X-ray Grazing Incidence Diffraction (GID)
] In-plane surface structure
Diffraction Pattern of Dry Pits
Hexagonal Packing
Liquid Fills Pore:
Scattering Decreases:
Thickness D~
Cross over to other filling!
X-ray Measurement of
Filling
GID
Reflectivity
Filling
Electron Density vs.....
T
Filling
Results for
Sculpted Surface
Sculpted is Thinner than Flat
c ~ T
c
Flat Sample
R-P Prediction
c~3.4
c
Uncertainties?
Tasinkevych & Dietrich
Volume of
Liquid Filling
Pores: p
Volume of Liquid
above Pores: t
Film only coats Flat Part
Area_Flat/Area Total:
l hmax
l hliq
Reconstructing
Surface:
Gold Nanoparticles
& Controlled Solvation
OT: MPA (2:1)
OT=CH3(CH2)7SH
MPA=HOOC(CH2)2SH
Controlled Wetting:
Dry Monolayer Adsorption
Langmuir
Isotherms
Stellacci et al (MIT)
Formation
Liftoff Area
Of Monolayer
Bimodal Size Distribution of Particles
GID: X-ray vs. Liquid Adsorption
(small particles)
Adsorption
GID
Return to Dry
Qz
Qxy
Qxy
Qxy
Temperature Dependence
of Reflectivity:
Three FeaturesThat
Can Be Understood!
1-Minimum at
low qz
2-Principal Peak
Reduces and Shifts
Solid lines are just
guides for the eye!
3-2nd Minima Moves
to Lower qz
Construction of Model: Dry Sample
Model Fit: Based on Particle Size Distribution
Vertical electron
density profile
Core size distribution
Fits of Physical Model
1-Minimum at
low qz
2-Principal Peak
Reduces and Shifts
3-Second Minima Moves
to Lower qz
Evolution of Model with Adsorption
Thick
wetting
film regime
Beginning of
bilayer transition
Thin wetting
film regime
Summary of Nano-particle experiments
Bimodal Au nanocrystals in equilibrium with undersaturated vapor
DRY
Good Solvent
Reversible
toluene T ~ 3 K
Poor vs..... Good
(1) dry
Solvent
(2) ethanol T ~ 1 K
Aggregation
in Poor
Solvent
toluene T ~ 0.5 K
(3) ethanol T ~ 15 mK
toluene T ~ 15 mK
QuickTime™ and a
(4) dry againTIFF
(etOH
extracted)
(LZW)
decompressor
are needed to see this picture.
toluene T ~ 0.5 K
(5) toluene T = 15 K
(6) toluene T ~ 15 mK
Dissolution
in Good
Solvent
toluene T ~ 3 K
(7) toluene T ~ 3 K
Self Assembly
Summary
•
•
Delicate Control of Wetting:
Wetting of Critical Liquid (Casimir)
M. Fukuto,Y. Yana
•
Wetting of Structured Surface (Rascon/Parry &
Tasikevych/Dietrich)
O. Gang, B.Ocko,, K.Alvine, T. Russell,M. Fukuto, C. Black
•
Nano-Particles: Self Assembly
D. Pontoni, K. Alvine, A. Checco, O. Gang, B. Ockio, F. Stellacci