Pests of mustard_Identification_Management_Dr.UPR.pdf
How Morphology Changes Bonding in Soft Materials: A Revelation Through Synchrotron Studies
1. Alokmay Datta
Saha Institute of Nuclear Physics,
1/AF Bidhannagar, Kolkata 700 064, India
How Morphology Changes Bonding in Soft
Materials:
A Revelation through Synchrotron Studies
2. Co-workers
Saha Institute of Nuclear Physics
Sudeshna Chattopadhyay (Northwestern University, USA)
Smita Mukherjee
Nupur Biswas
TASC-INFM National Laboratory and UniVersita` di
Modena e Reggio Emilia
Stefano Nannarone
Angelo Giglia
Nicola Mahne
Bryan Doyle
3. A Question about Soft Materials
Soft Materials show drastic change in morphology when
confined to nanometer scales in all or any dimensions
Formation of monomolecular layers at air-water interface
and their restructuring in presence of metal ions
Formation of molecular layers parallel to the surface in films
of simple and complex fluids including polymers, below a
certain film thickness
Bonding or electron distribution in materials depend on the
molecular conformation
Does change in morphology cause change in
molecular conformation?
4. Experimental Techniques Used
Studies at Saha Institute
•X-ray Reflectivity – Density Profile across the sample
•Atomic Force Microscopy – Surface Topography and Surface
Energy Distribution
•Infrared Spectroscopy – Bonding and Conformation
Studies at Elettra
•Vacuum Ultraviolet Spectroscopy – Conformation
•Near Edge X-ray Absorption Fine Structure Spectroscopy –
Bonding
6. Fluids: Simple and Complex
Simple Fluid
Intermolecular potential
1. Spherically symmetric
2. Short range
Isotropic and Viscous
Complex Fluid
Intermolecular potential
1. Anisotropic
2. Long/short range
Anisotropic and Visco-elastic
7. X-ray Reflectivity: PrinciplesReflectivity: Principles
•In x-ray region, refractive index n < 1, i.e.,
phase velocity of x-rays in material > phase
velocity in vacuum.
total external reflection (specular reflection)
Incident and scattered wave-vectors in same plane normal to surface
Incident angle (α) = scattered angle (β)
δ∼10-6
, ρ → electron density, r0 → classical electron radius ~ 2.8×10-5
Å
•n = (1-δ) =1-(ρr0 λ2
/2π )
•qz = normal momentum transfer = kf - ki= 4π/λ(sinα)
∀αc = critical angle for sample film = (2 δ)½
z
x
At α > αc, x-rays penetrate into sample, are scattered for each change in
ρ, and these scattered x-rays interfere interference (Kiessig) fringes in
reflectivity profile with periodicity 2π/d, d = thickness of a layer with a
constant ρ, while amplitude of fringes ∝ change in ρ
kt
ki kf
α α
β
n = 1-δ
n=1
8. ∆qz = 2π/d
d
Air
Film
Substrate
Interference (Kiessig) fringes with periodicity 2Interference (Kiessig) fringes with periodicity 2ππ/d, d = thickness of/d, d = thickness of
a layer with a constanta layer with a constant ρρ, while amplitude of fringes, while amplitude of fringes ∝∝ change inchange in ρρ
M. K Sanyal, A. Datta, S. Hazra, Pure Appl. Chem. 74, 1553 (2002).
The Reflectivity Profile
9. Mirror
Laser
Diode
Focusing Lens
Piezo Scanner
Sample
Holder
Integrator
Divider /
Multiplier
Differential
amplifier
4-quadrant PSPD
X-Y Translator
X Y
Tip
SampleCantilever
Force
attractive force
distance
(tip-to-sample
)
repulsive force
non-contact
contact
Intermittent-
contact
Multimode Nanoscope IV
(Digital Instruments)
Intermittent-Contact (tapping) mode; Etched Si tip; Phosphorus-doped Si
cantilever; Force constant 40N/m; Characteristic frequency 344kHz
Atomic Force Microscope
10. Layering in Simple Fluids: TEHOS
C.-J. Yu, A. G. Richter, A. Datta, M. K. Durbin, and P. Dutta, Phys. Rev.
Lett. 82 , 2326 (1999).
This work used the National Synchrotron Light Source, USA as the X-ray source
12. Sample preparation: Spin CoatingSample preparation: Spin Coating
Spin Coating Unit, EC101, Headway Research
Thin films are prepared by putting a drop of solution in toluene on
acid-washed quartz mounted on rotating vacuum chuck.
Film thickness can be varied by adjusting the rotation speed and
concentration of the solution
13. Surface Energy Variation from Phase
Measurement
000
sin
kAA
QE
A
A D
πω
ω
φ +
=
SiPS
Sic
D A
z
r
E ∆=∆ 2
0
3
2 α
2/12
2/12/1
4
∆
−
∆
=∆
Si
SiPS
PS
Si
SiPS
H
A
A
A
A
A
A
Tip Parameters: φ = phase, ω (ω0) = working
(resonant) frequency, A (A0) = set-point (free)
amplitude, k = spring constant, Q = quality factor,
ED = energy dissipated per cycle, rc = radius of
curvature, αSi = Si atomic radius, ASi = Si Hamaker
constant z0 = Tip-sample separation,
ASiPS = Si-PS Hamaker
constant, APS = Bulk PS
Hamaker constant, AH = PS
Hamaker constant in film
J. Tamayo and R. Garcia, Appl. Phys. Lett. 73, 2926 (1998).
14. First Indication of Layering
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
10
-10
10
-9
10
-8
10
-7
10
-6
1x10
-5
1x10
-4
10
-3
10
-2
10
-1
10
0
10
1
Electrondensity,ρ
z (Å)
Reflectivity
qz
(Å
-1
)
0 200 400 600 800
0.28
0.32
0.36
0.40
0.26 0.28 0.30 0.32 0.34 0.36
500
400
300
200
100
0
Depthfromsurface
Electron Density (Å
-3
)
~212 Å ~Rg
Rg is the radius of gyration of
Polystyrene, i.e. the size of the
Polystyrene molecule in its most
Disordered state
M. K. Sanyal, J. K. Basu,
A. Datta and S. Banerjee
Europhys. Lett. 36, 265 (1996)
16. Nanoconfined State: An Ordered State with Low
Cohesion (Out-of-plane)
S.Chattopadhyay and A.Datta, Phys. Rev. B 72, 155418 (2005)
Reduction in cohesive energy caused by the variation of density due to layering
∆AH= σPS (ρmax
2
- ρmin
2
), δ = (ρmax - ρmin), AH = Hamaker Constant
17. Lowering of In-plane Cohesion in Nanoconfined
Polystyrene
Polystyrene
Thickness
~7Rg (150 nm) 4Rg (84 nm) ~2Rg (50 nm)
∆γPS = the change in PS Surface Energy
∆GPS –PS = the change in in-plane PS cohesion
S. Chattopadhyay and A. Datta, Macromolecules 40, 3613 (2007)
18. Intermolecular Potential in Nanoconfined State
From X-ray Reflectivity (Out-of-plane)
∆G (in mJm−2
) ≈ ∆AH (in J)/(2.1×10−21
)
Spatial variation in ∆G fits the Modified Pöschl-Teller Potential
∆GPS−PS(ξ) = V0 cosh-2
(ξ/Λ), ξ = generalized co-ordinate,
Λ = range of potential
Polystyrene film thickness shown beside each curve
From Atomic Force Microscopy (In-plane)
20. Nanoconfinement and Molecular Conformation
The non-zero dihedral angle has non-zero dipole moment,
whereas the dipole moment vanishes as the dihedral angle becomes zero
21. Orientational Ordering of Benzene Rings on
Confinement
The benzene ring ‘sandwich dimers’ are oriented 63° with the sample surface
22. Confinement versus Entanglement
PS D1/D2 δ (eÅ-3
)
PS-1C 0.69 0.131
PS-5C†
1.061 0.045
PS-9C 0 0
D1 = out-of-plane periodicity as obtained from GIXR data
D2 = in-plane diameter of gyration ‘spheres’ as obtained from TM-AFM images
δ = average difference between electron density maxima and minima in the layered
‘spheres’ as obtained from EDP
†Phy. Rev. B, 72, 155418 (2005)
δ → 0 as MW increases
23. Conclusions
Confinement causes change in morphology
through change in molecular conformations
These changes may give rise to new
intermolecular potentials
The new conformations and consequent forces
are seen to lower the entropy by orientational
ordering
In polymers increase in chain length increases
‘entanglement’, possibly a force opposing
confinement induced changes
