Dynamics of Nanoparticles
(borrowing, as Nano often does, from Macromolecular)
Your career = Techniques X Problems
Problems
This talk concerns
Techniques
Tomas Hirschfeld: Most people work only on techniques, but not
on finding problems. But remember, your career will be the vector
cross product of techniques you learn and problems you choose.
Why do we need dynamics for
nanoparticle characterization?
1. Dynamics give us size
Microscopy does not always measure size well.
Microscopy cannot follow rapid size/shape changes well—e.g.
self-assembly.
Microscopy may alter the materials being studied.
Small angle X-ray scattering and small angle neutron
scattering are slow, expensive, can damage samples,
and sometimes have contrast issues.
2. Dynamics tells us basic information
Stability of structures: scaffolds to slow the kT problem
Internal viscosity inside devices: how fast can nanodevices
work?
Dynamics Techniques
 DLS = Dynamic light scattering
 FPR = Fluorescence photobleaching recovery
 AUC = Analytical ultracentrifugation
 DOSY = Diffusion ordered NMR spectroscopy
(not this trip—takes too long to explain)
DLS = Dynamic Light Scattering
• If you look closely at light scattered by a
sample, it fluctuates.
• Some of that is just DUST, a nuisance, but
some fluctuations are interesting.
• The fluctuations represent how quickly the
molecules are moving.
• This is tracked with a “correlation function”
Correlation Function
1
g (t )  E (0) E (t )  lim
T  2T
T
 E (t ' )  E (t 't )dt '
T
Where E(t) is the instantaneous electric field of the scattered light
t=0
E(t)
<E 2>
Thus, correlation
Functions DECAY
with time!
t’
t =
0
Quick decay = fast mover = small particle
g (t )
Slow, big
G = decay rate (Hz)
Fast, small
t
An exponential becomes a sigmoidal curve if
you change the x-axis to logarithmic.
g (t )
Fast, small
Slow, big
Log( t )
G comes from inflection point.
Dynamic Light Scattering
LASER
GUv = q2Dtrans

V
LASER

V
H
GHv = q2Dtrans + 6Drot
q
4n sin / 2 
o
Uv Geometry
(Polarized)
Hv Geometry
(Depolarized)
FPR = Fluorescence Photobleaching
Recovery
• First, measure fluorescence: step F
• Then photobleach (“erase”) some with a bright
flash of light: step P
• Then observe recovery due to diffusion: step R
The sample has to be fluorescently labeled.
Destruction of the label must not damage the nanoparticle.
Blue input light
Green
Detected
Light
Fluorescent
Sample
Fluorescence & Photobleaching
Blue input light
Green
Detected
Light
Slowly Recovers
Fluorescent
Sample
With Fluorescence
Hole in Middle
Recovery of Fluorescence
Modulation FPR Device
Lanni & Ware, Rev. Sci. Instrum. 1982
SCOPE
5-10% bleach depth
IF
PA
c
X
TA/PVD *
PMT
*
D
S
*
DM
OBJ
M
RR
*
M
ARGON ION LASER
AOM
* = computer link
Cue The Movie
The FPR contrast decay resembles DLS.
Contrast (t )
Slow, big
G = decay rate (Hz)
Fast, small
t
AUC = Analytical Ultracentrifugation—a Good
Way to Characterize Self-assembled Species
Sealed dual beam UV-Vis cell
Rotor (side perspective)
Spins at up to 60,000 rpm
Sedimentation: simple gravity + thermo
r = a; meniscus

Svedberg
Nobel Prize
Chemistry, 1926
r = b; bottom
Fb
Fd
Fc
r
2
Igor-Bricker sample
c(r )  c(a) exp(
 2 M (1  v~2 )(r 2  a 2 )
2RT
)
Absorbance
o
T=20.0 C
24,000 RPM v2=0.73 mL/g
1
0
40
45
2
2
r /cm
50
OK, so let’s look at 5 applications
1.
2.
3.
4.
5.
Can we measure the viscosity in a nanoreactor? (DLS)
Can we watch a bio/nano particle change? (DLS & LS)
Nanotech needs scaffolds: will they stand still? (FPR)
Controlling self assembly. (DLS)
Making a word using one of the most fascinating of the
new nano alphabets. (AUC)
Some of this is published:
See http://macro.lsu.edu/russo  research articles link
ZADS = special form of DLS
PTFE latex microrheology of polyacrylamide gel
2.0
PTFE Particles
470 s
g(2)()
1.8
1.6
~ 250 nm
1130 s
1.4
1340 s
1.2
1630 s
1.0
1E-6
2470 s
1E-5
1E-4
1E-3
0.01
0.1
1
10
/s
Camins & Russo, Langmuir, 4053, 1994
See also: Piazza, Tong, Weitz
1
Fraction Frozen by Gelation
More ZADS
1.0
0.8
1
0.6
0.4
0.2
0.0
0
1000
2000
Time/s
3000
1
Seedlings
Sick Plants 
And close-up
of mosaic
pattern.
http://www.uct.ac.za/depts/mmi/stannard/linda.html
What we have been trying to do:
rotation and translation of a TMV
through “random coil” solutions.
Very hard to do right!
1. Cush et al. Macromolecules 1997.
2. Cush & Russo Macromolecules, 2004
(in press, probably December)
1
Drotation ~ h-1 & Dtranslation ~ h-1
Bottom line: TMV or nanoparticles can report the
viscosity more or less accurately in a small system.
h T
h R
100
h
1
h/cP
0.76 ± 0.01
10
(C)
1
100
1000
10000
100000
Dextran MW
1000000
1E7
“Virions are usually roughly spherical
and about 200nm in diameter.
The envelope contains rigid "spikes"
of haemagglutinin and
neuraminidase which form a
characteristic halo of projections
around negatively stained virus
particles. “
Linda Stannard, of the Department of
Medical Microbiology, University of
Cape Town
http://web.uct.ac.za/depts/mmi/stannard/fluvirus.html
“The Flu”
2
Guinier plots. ILS vs. q2
5.4
From910921
pH 7.4 900 Åph 7.4 900 ± 30 Å
From924935
pH 5
1330 ph
Å 5 xxx min 1330 ± 30 Å
pH 5 later 1710 ph
Å 5 xxx min 1710 ± 50 Å
From938949
5.2
5.0
4.8
ln(I/arbitrary)
4.6
4.4
2
4.2
4.0
3.8
3.6
3.4
3.2
o
 = 45
3.0
o
 = 90
2.8
2.6
0
2
4
2
10
q /10 cm
6
2
8
Dynamics of Flu “opening up”: Addition of citric acid
for pH change is shown by the line at time 0.
200
1200
180
160
1000
140
120
100
600
80
400
60
Rh
200
40
Intensity
20
0
0
-400
-200
0
200
400
t /s
600
800
1000
1200
1400
Intensity/kcps
Rh /Å
800
2
pH 
Sproing!!!
2
Forms a reversible gel scaffold.
PSLG: poly(stearyl-L-glutamate)
O
O
3
Temperature-ramped
modulation FPR
20
700
30
40
scan1062
combinehigh
50
2
DDSC
4
Contrast (AC/DC)
500 3
2040 s
DSC
start ramp @
0.3oC/min
400
AC/DC
DSC (W) or DDSC+600 ( W/ oC)
600
2
300
TRFPR: 30.7oC
200 1
1
Melt at 30.9oC
100
0
0 0
20
1000
2000
30 t (seconds)
T/ oC
3000
40
Schmidtke et al.
50
Figure 6
Schmidtke et al.
Figure 7
3
Everything can move,
yet the structure remains.
Means that even though you
have built a scaffold (for
example, to grow artificial
skin or hold a sensor or drug
delivery nanomachine in
place) and even though it
may seem to hold its shape,
you must be careful!
This kind of molecular view of gelation is not available
from mechanical methods, such as rheology.
3
Observe Control of Self-assembly
Bolaform amphiphiles have
a dumb-bell shape
hydrophilic
hydrophilic
hydrophobic
4
Arborol example: [9]-10-[9]
4
9 watery hydroxyl
groups
OH
HO
HO
H
N
HO
HO
HO
HO
HO
HO
HO
N
H
O
O
10 oily
methylene groups
O
N
H
O
O
OH
H
N
OH
OH
O
N
H
H
N
OH
OH
OH
OH
OH
Arborol properties
• Dissolve in warm
water.
• Gel on cooling—
Why? How?
• Apparently, they are
“real gels”
• Fibers inside the gels
.
• Self-assembly
• Reversible
4
Why do we care?
Self-assembling system
Reversible
Easy to vary headgroup and core size
Possible applications in:
• Porous media
• Stationary phase for separations
• Reversible, rigid rods  dynamic liquid
crystals we can manipulate
• Disease-inspired microfluidics—can we
simulate sickle cell anemia?
4
Dendrimer self-assembly challenges
• Can we control self-assembly? Synthesis!
Terminator
• How would we know? Analysis!
• What if we did? New Physics & Materials!
4
Self-assembly of [9]-12-[9] by DLS
4
Self-assembly of Dilute Arborols—Rh
1300
[9]-10-[9]only
[9]-10-[9] plus [9]-6
1200
1100
Rh/(Å)
1000
900
800
700
600
500
400
0
1
2
Number of Days
3
4
Rh got from linear fit of
gamma vs q2 of DLS data
at five angles:
40, 50, 60, 70 and 90.
New problem: Hexaruthenium
terpyridyl supramolecular structures
Newkome et al.
Angew.Chem.Int.Ed.
1999, 38(24) 3717-21
5
2 is the
key monomer for
the supramolecule.
5 aids in
Proof of structure.
Molecular snowflake by two methods
5
Data on supposed snowflake supports several
scenarios, but self assembly surely occurs
5
Same Data, Different Analysis
0.006% (low!)
0.5% (NMR conc.)
M = 2600
80% @ M=1340
M=3250
20% @ M=5600
+ non-sedimenting stuff
Write the terpyridyl aggregate in
shorthand form.

5
We see evidence of aggregation
by SAXS, confirmed by DLS.
n
Note that this alphabet
retains symmetry similar to
the atomic alphabet
5
Stacked disks?
?
Continue
In this way
to make
aggregates of
aggregates of
aggregates
etc.
Conclusions
The power of DLS, FPR and AUC has been
demonstrated.
It was my purpose to familiarize you with these
tools….but maybe I accidentally showed you
some good problems to study as well.
Maybe you can see a new vector cross product
somewhere.
The terpyridyl ruthenium business is an example
of a supramolecule; however, the proponents
of supramolecular thinking have less influence
than the nano people. So…it must be nano!