SELFASSEMBLY FOR NANOMANUFACTURING

1
SELF-ASSEMBLY FOR NANOMANUFACTURING
Presentation at Indo-US Forum on Advanced and
Futuristic Manufacturing IIT/Kanpur, March 22,
2004 Arijit Bose Department of Chemical
Engineeering University of Rhode Island Kingston,
RI 02881 bosea_at_egr.uri.edu [phone]
2
ACKNOWLEDGEMENTS
Collaborators Profs. V. John,. G. McPherson -
Tulane Graduate students at Tulane B. Simmons,
M. Singh, L. Liu Graduate students at URI V.
Agarwal, R. Lawton N. Balsara (UC Berkeley), B.
Hammouda(NIST), T. Lee(MIT) A. Nunes(URI)

• National Science Foundation
• NIST
• Cabot Corporation

3
OUTLINE

• Self-assembly of soft colloids
• Direct and reciprocal space imaging
• Templated synthesis from self-assembled
  nanostructures
• Hierarchical assembly of nanotubes
• Layer-by-layer assembly
• Challenges

4
SELF-ASSEMBLY - SURFACTANTS
5
TEMPLATED SYNTHESIS FOLLOWING SELF-ASSEMBLY
Hentze and Kaler, Chem. Mat, 15, 708 (2003)
6
IMAGING OF SOFT NANOMATERIALS

• CHALLENGE
• Aggregate size 5 100nm, not electron dense,
  phase behavior is concentration dependent

• COMPLEMENTARY POTENTIAL SOLUTIONS
• Small angle neutron scattering (SANS)
  reciprocal space imaging
• Freeze fracture direct imaging (FFDI) direct
  imaging
• Cryogenic transmission electron microscopy
  (cryo-TEM) direct imaging

7
MIXED SURFACTANTS - GEOMETRIC
p v/al
p lt 1
Lecithin
p gt1
AOT
Up to water/AOT 230 without phase separation
8
THE SYSTEM
Percolation threshold
Probe microstructures using neutron scattering
9
NEUTRON SCATTERING
Water core
Deuterated water
chosen
water
surfactant
Water core surfactant layer
Deuterated isooctane
isooctane
Deuterated water and deuterated isoctane
(contrast matched)
Surfactant layer
10
SMALL ANGLE NEUTRON SCATTERING - SANS
sample
Neutron source
neutron beam
2q
detector
Wavelength selector
q (4 p /l) Sin(q/2) d 2 p/q, l 6Å To
probe 50Å lt d lt 1000Å 0.35º lt q lt 7º ? small
angles
Sample to detector distance 2m 13m
11
SANS
W0130
1200
1000
800
250C
Intensity(cm-1)
600
400
200
0
0
0.01
0.03
0.05
0.07
0.09
q(Å-1)
12
SANS
L Lamellar
H Hexagonal
70
H
T
L
L
L
L
L
55
H
T
T
L
L
L
21
H L
Temperature (0C)
40
H
H
H
T
L
L
H
25
H
H
H
H
T
T
Lamellar
70
90
110
130
150
170
W
o
?31
q (Å-1)
Hexagonal
Transition
HexagonalLamellar
Langmuir, 18, 624 (2002)
13
SHEAR SANS
neutral (vorticity)
gradient
flow
neutral (vorticity)
Boulder Couette flow cell
gradient
tangential
radial
neutral (vorticity)
R
T
shear rate
flow
time
14
SHEAR SANS
L Lamellar
H Hexagonal
70
H
T
L
L
L
L
L
55
H
T
T
L
L
L
H L
Temperature (0C)
40
H
H
H
T
L
L
H
25
H
H
H
H
T
T
70
90
110
130
150
170
W
o
15
POTENTIAL CONFIGURATIONS- ALIGNMENT
Hexagonal
two-fold symmetry
tangential
radial
six-fold symmetry
A
Lamellar
C
B
neutral
neutral
gradient
flow
radial
tangential
radial
tangential
radial
tangential
16
SHEAR SANS, WO70 (hexagonal), 41C
0s-1
38.9s-1
116.7s-1
0s-1
0s-1
3.89 s-1
RAD
neutral
flow
40min
6min
TANG
neutral
gradient

• Rods align in direction of flow
• Shear induced alignment
• Recrystallization

17
SHEAR SANS, WO170 (lamellar), 41C
6min

• Polycrystalline pattern
• No additional ordering because of shear
• No crystallization

18
FREEZE FRACTURE DIRECT IMAGING
EM grid placed over sample
EM grid
sample
Copper planchette
Liquid ethane
Liquid nitrogen cooled cryotransfer stage
19
FREEZE FRACTURE DIRECT IMAGING
100 nm
100 nm
100 nm
100 nm
W070
W030
W0200
100 nm
100 nm
100 nm
W0130
W0130
Langmuir, 20, 11 (2004)
20
SELF ASSEMBLY IN MIXED SURFACTANTS

• Mixed cationic and anionic surfactants in water
  SELF-ASSEMBLE into a range of stable aggregate
  structures - micelles, vesicles, lamellar liquid
  crystalline phases
• Self-assembly dynamics?
• Pathways?
• Intermediate state structures?
• Models for biomembranes
• Encapsulants for drug, fragrance delivery

21
SELF-ASSEMBLY - ELECTROSTATIC
Na OS-
CTA Br-
CTAB/SOS
16/8
22
MICELLES AND VESICLES
micelles
vesicles
micelles
23
TIME-RESOLVED TECHNIQUES
A
B
time

• Turbidity
• Dynamic light scattering
• Cryo-TEM

24
CRYO TEM
C
R
Y
O

T
R
A
N
S
F
E
R

S
Y
S
T
E
M
C
r
y
o
-
s
t
a
g
e
W
o
r
k
s
t
a
t
i
o
n
Ethane MP -183C BP -89C Nitrogen MP
-210C BP -196C
25
MICROSTRUCTURE EVOLUTION
100nm
B C ? A
8min
12min
120min
47min
26
STAGE-TILTING EXPERIMENTS
Image plane
disks
vesicles
27
STAGE TILTING
100nm
30
28
CTAB/HDBS
100nm
11min
7min
60min
37min
29
NON-EQUILIBRIUM STRUCTURES- MICELLE-VESICLE
TRANSITION
micelles
disks
Useful?
small vesicles
final vesicles
30
DOPE CTAB MICELLES WITH 4-ETHYL-PHENOL
Low dissociation constant Vary concentration
without affecting ionic strength
CTA Br-
31
CTAB/4-Ethyl phenol/Water
1 0
3 1
Wormlike micelles
1 3
Spherical micelles
1 1
100 nm
Vesicles
vesicles
Multi-vesicles, tubules
32
CTAB/4-Ethyl phenol/Water
CTAB4-Ethyl phenol 11
33
CTAB/4-Ethyl phenol/Water
34
SELF ASSEMBLY

• Only economical method for going from nano to
  micro and perhaps macro scale
• Nature is the ultimate self-assembler
• It is not necessary to be molecularly precise for
  successful self-assembly - need an average amount
  of self-correction
• Current state-of-the art is molecular
  architecture chemistry self assembly
• hydrogen bonding, electrostatic forces and van
  der Waals interactions
• We are at a very rudimentary level as far as
  manufacturing using self-assembly is concerned
• Goal - put all parts of the Taj Mahal into a big
  pot, and out comes the final structure!!

35
TRANSCRIPTIVE SYNTHESIS - SILICA
Tetraethoxysilane (TEOS) hydrolyzes at the
surfactant- water interface
TEOS
Tetra ethoxy silane
water
IsooctaneTEOS
4 days
Si(O Et)4 2H2O ? SiO2 4 EtOH
12 TEOSIO, WO90
Silica synthesized in the gel
Gel with precursors
36
THIN SECTION TEM - SILICA
J. Dispersion Sci and Tech.  23, 441 (2002).
37
UNSHEARED AND PRESHEARED SILICA
Sheared material
J. American Chemical Soc., 126, 2276 (2004)
38
TRANSCRIPTIVE/RECONSTRUCTiVE - PMMA SYNTHESIS
Lamellar phase AOTlecithin 12
Microstructure stays robust during polymerization
39
POLYMER/NANOPARTICLE COMPOSITE - RECONSTRUCTIVE
water
MMA IO AIBN
Viscous gel (particles spatially immobilized in
nanochannels)
Fe(OH)2
FeCl2solution
MMA IO AIBN
heat
NH4OH solution
microemulsion
MMA methyl methacralate IO Isooctane AIBN
free radical initiator
PMMA/Fe(OH)2 nanocomposite
40
MATERIALS SYNTHESIS (CdS)

• Microemulsion precipitation aqueous
  solution/IO/AOT (lecithin)
• Wt 10
• Water pools 0.1M cadmium chloride, 0.05M
  sodium sulfide

?
AOTPTC0.05M
AOT0.1M
Aspect ratio 115
Nanoletters, 2, 263 (2002)
TEMPLATING?
41
TEMPLATED SYNTHESIS
42
TEMPLATED SYNTHESIS - 3D ORGANIZATION
43
NANOMESH FORMATION
Y. Lu, Tulane
44
CARBON NANOTUBE - DIRECTED GROWTH
G. Ramanath, RPI
45
SITE-SELECTIVE NANOTUBE GROWTH
G. Ramanath, RPI
46
TEMPLATELESS SELF-ASSEMBLY

• Viscositycontrols cluster mobility and
  impingement rate
• Surface passivationinhibits coalescence
  controlled by solvent molecular structure
• Possibility to tune microstructures

G. Ramanath, RPI
47
LAYER-BY-LAYER ASSEMBLY






-
-






























-

-

• Polyelectrolytes
• Proteins
• Nanoparticles
• Substrate can have any morphology

Decher Lvov Rubner Hammond
48
SOME THOUGHTS AND CHALLENGES

• Powerful techniques are now available for imaging
  microstructures in soft materials (cry-TEM, FFDI,
  SANS, LS..)
• Rational materials synthesis for nanostructured
  materials, organized over multiple length scales
• External fields - shear, magnetic, electric
  fields to affect mesoscale morphology,
  functionality?
• 3-D assembly of nanomaterials

49
THANK YOU!!
50
DISK? SMALL VESICLE TRANSFORMATION
edge
Membrane area A p L2

• Ebend k (A/2) (2C 2Csp)2 2 p k (L C -
  LCsp)2
• C curvature, Csp spontaneous curvature, k
  bending modulus
• Eedge 2 p l L 1 - (LC/2)21/2
• edge energy/length
• x k / l

Etotal / 2pk E (LC - LCsp)2 L/x1 -
(LC/2)21/2
51
ENERGETICS OF DISK? VESICLE TRANSITION
5
L/x
8
L/x
4
4
?E
1
1

• Energy barrier for vesicle formation vanishes at
  L Lcritical
• Lcr/x 8 / 1 (4Csp x)2/33/2
• D0 Lcr, Deq 2/Csp,

D0-2/3 Deq-2/3 (8x)-2/3 x k/l
CTAB/SOS moderate x, CTAB/HDBS x gtgt 1
52
SELF-ASSEMBLY - MORPHOLOGY CONTROL
G. Ramanath, RPI
53
LAYER-BY-LAYER ASSEMBLY






-
-






























-

-























Y. Lvov, LA Tech