2. What I would like to talk about
Liquids
When liquids do not behave as ‘liquids’
How to ‘know’ a liquid
Langmuir monolayers and multilayers
‘Solid-like’ and ‘liquid-like’
Polymer films
‘long-rod’ and ‘short-rod’ liquids
3. My c0-workers
My Students (Past and Present)
Sarathi Kundu, Institute of Advanced Study in Science & Technology, India
Sudeshna Chattopadhyay, Northwestern University, USA
Smita Mukherjee, Indian Institute of Technology, India
Nupur Biswas
From Saha Institute
Milan K. Sanyal
Munna Sarkar
Mrinmay Mukhopadhyay
From Kyoto University
Masatoshi Ichikawa
Kenichi Yoshikawa
5. Simple & Complex Liquids
Water
Liquid metals
Polymers
Liquid crystals
Colloids
Surfactants
Lipids
Intermolecular Potential
Spherically symmetric
Short range
Isotropic and Viscous
Intermolecular Potential
Absence of symmetry
Long/Short range
Anisotropic and Visco-elastic
6. Bulk Liquids
Solid Liquid Gas
Energy per particle increases
Order increases
Bulk liquids, either complex or simple, can be identified as ‘liquids’
from their mechanical properties
For confined liquids, however, it is not easy to do that
We need to take recourse to structural correlations
8. Liquid Surface and Films
For liquid surface molecules exhibit capillary fluctuations
Motions due to gravity and thermal energy.
This gives rise to a height-height correlation of the liquid surface,
whether the liquid is bulk or confined
This correlation has a continuous spectrum of periodicities, the lowest being the
molecular size and the highest being the size of the liquid or film body
This correlation depends logarithmically on r, the separation between the heights
Unbalanced force pulls the
surface molecules inward.
Surface Tension
9. Self-affine Surfaces
]})/(exp[1{2)( 22
0
H
Lrrg
These surfaces are created by fractional Brownian motion.
On them N steps taken with step-size r to cover the length of a curve,
implies that the curve at that scale has length l = Nr, with N = C/rD, 0<D<1.
They have the typical height-height correlation given by
11. Confined Liquids
Confined simple liquids
Ordered state of matter
What happens to the complex liquids, such as Langmuir films and polymers ?
12. Monolayers on Water Surface – ‘Solid’-like
π = 5mN/m
CdSt – irreversible fracture behaviour
π = 30mN/m
With cadmium ions
in subphase, stearic
acid monolayer, when
compressed (up
to π = 30 mN/m),
shows the formation
of “crystallites” that
remain unaffected
when decompressed
from π = 30 mN/m
to π = 5 mN/m.
The CdSt monolayer at 5 mN/m
distinctly shows the presence of a
monolayer on which crystallites are
formed.
13. Monolayers on Water Surface – ‘Liquid’-like
π = 30mN/m π = 5mN/m
CoSt – soap bubble-like behaviour
In the presence of
cobalt ions, on
the other hand, the
monolayer “spreads
out” gradually as π
changes from 30
mN/m to 5 mN/m
and forms completely
interconnected “soap-
bubble-like” features
on decompression.
These aggregate
continuously to form
the monolayer on
recompression.
These decompression and recompression behaviours
of Langmuir monolayers with cadmium and cobalt
ions in subphase suggest, respectively, the essentially
irreversible fracture of a solid and the reversible,
interconnected-bubble features of a soapy liquid.
15. Monolayers on Solid Surface – ‘Liquid’-like
CoSt – liquid-like behaviour
1ML 3ML3ML
Logarithmic function
f (r) = d ln(ar2 + br + c)
16. The Parameters
CdSt Film
Scan size (μm) σ (A° ) L (nm) H
1 ML 0.5 34.0 4.4 0.83
1.0 35.0 2.8 0.76
2.0 39.3 1.3 0.74 3
ML 0.5 39.0 15.9 0.75
1.0 49.0 6.4 0.72
2.0 47.3 1.4 0.78
5.0 35.0 0.3 0.78
10.0 48.0 0.1 0.85
CoSt Film
Phys. Rev. E 84, 021606 (2011)
17. What kind of ‘Liquid’ is this?
Phase Images
CdSt
CoSt
‘domains’
‘waves’
CdSt CoSt
18. Why Does this Happen – Role of Molecular Dipoles
CoSt – No Molecular Dipoles
No Long-range Forces
CdSt –Molecular Dipoles
Long-range Forces
Phys. Rev. E 83, 041604 (2011).
21. 400 600 800 1000 1200
0.00
0.04
0.08
0.12 PS2C
PS5C
(eÅ
-3
)
Film Thickness, d (Å)
Confinement versus Entanglement – Role of
Molecular Weight
400 600 800 1000 1200
0
50
100
150
200
250
PS2C
PS5C
AH
(meV)
Film thickness, d (Å)
Phy. Rev. B, 72, 155418 (2005), Macromolecules, 40, 9190 (2007)
δ = order parameter= ρmax-ρmin AH = Hamaker constant cohesive energy
With increasing molecular weights i.e. chain lengths layering vanishes.
There exists a competition between ‘entanglement’ and ‘confinement’.
AH= PS (max
2 - min
2)
22. -50 0 50 100 150
0.0
0.2
0.4
0.6
Electrondensity(eÅ
-3
)
Depth from the surface (Å)
pristine film
buffered film
Confined Charged Polymer
0.0 0.2 0.4 0.6 0.8
10
-9
10
-7
10
-5
10
-3
10
-1
10
1
10
3
buffered film
Reflectivity
qz
(Å
-1
)
pristine film
Pristine film no counterion, Buffered film 10mM buffer added. 1 buffer molecule 1 Na+ ion
5.06 nm
0.00 nm
5.06 nm
0.00 nm
0.00 Pi
-0.00 Pi
-
16.81 nm
0.00 nm
0.00 nm
16.81 nm
-
0.00 Pi
-0.00 Pi
Pristine film Buffer film
Pristine film has three layers
- simple liquid like
Counterions in buffered film
destroys layering – polymer like
Communicated
23. 10
-5
10
-4
10
-3
10
-2
10
-1
10
0
DSC(Normalized)
qy
(Å
-1
)
21.8
o
21.5
o
21.2
o
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
2 = 1.8
o
2 = 1.5
o
2 = 1.2
o
DSC(Normalized)
qy
(Å
-1
)
Confinement versus Entanglement – Role of
Counter-ions
Communicated
Pristine film Buffer film
g (r) = <[ h(r0+r) – h(r0) ]2>
Height-difference correlation function,
Self-affine liquid like correlation function,
]})/(exp[1)]}{
2
ln([2{)( 22
0
H
E Lr
r
Brg
0= roughness, L =correlation length, H= Hurst exponent,
B= kBT/γ, γ = surface tension, κ = lower cut-off wavevector
Film 2θ κ (E-7)
(Å-1)
Pristine 1.2 5.01
1.5 6.0
1.8 6.527
Buffer 1.2 2.0
1.5 2.10
1.8 2.0
/2
g ∆ρ = density fluctuation
In buffered film along its depth density
fluctuation decreases - layering is absent.
Films have liquid like correlations.
DNA molecules behave as liquid of rods.
24. What next?
1. How do two 2D liquids mix – competition between entropy and interaction?
2. What is a ‘dried-up’ film: ‘Solid-like’ or ‘liquid-like’? What decides that?
3. Can thinning be treated at par with other ‘fields’ (temperature, pressure, etc.)
that cause phase transitions? How does it enter the energy term?