dynamics of nanoparticles (borrowing, as nano often does, from macromolecular)
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Dynamics of Nanoparticles (borrowing, as Nano often does, from
Macromolecular)
Techniques
Problems
Your career = Techniques X Problems
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.
This talk concerns
Why do we need dynamics for nanoparticle characterization?
1. Dynamics give us sizeMicroscopy 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 informationStability of structures: scaffolds to slow the kT
problemInternal 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
T
TT
dtttEtET
tEEtg ')'()'(2
1)()0()( lim
Where E(t) is the instantaneous electric field of the scattered light
E(t)
t’
t = 0
t =
<E 2>
0
Thus, correlationFunctions DECAYwith time!
Quick decay = fast mover = small particle
t
g (t )
Slow, big
Fast, small
= decay rate (Hz)
An exponential becomes a sigmoidal curve if you change the x-axis to
logarithmic.
Log( t )
g (t )
Slow, bigFast, small
comes from inflection point.
Dynamic Light ScatteringDynamic Light Scattering
Hv = q2Dtrans + 6Drot
LASER
VV HH
PMT
Hv Geometry Hv Geometry (Depolarized)(Depolarized)
Uv Geometry Uv Geometry (Polarized)(Polarized)
VV
Uv = q2Dtrans
o
nq
2/sin4
PMT
LASER
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.
Fluorescence & Photobleaching
Blue input light
FluorescentSample
Green Detected
Light
Recovery of Fluorescence
Blue input light
FluorescentSample
With FluorescenceHole in Middle
Green Detected
LightSlowly Recovers
Modulation FPR Device Lanni & Ware, Rev. Sci. Instrum. 1982
*
*
*
*
AOM
M
M
D
RR
DM
OBJ
S
PMT
PA
SCOPE
TA/PVD
ARGON ION LASER
* = computer link
IF
X
c
5-10% bleach depth
Cue The Movie
The FPR contrast decay resembles DLS.
t
Contrast (t )
Slow, big
Fast, small
= decay rate (Hz)
AUC = Analytical Ultracentrifugation—a Good Way to Characterize Self-
assembled Species
Rotor (side perspective)Spins at up to 60,000 rpm
Sealed dual beam UV-Vis cell
Sedimentation: simple gravity + thermo
Fb
Fd
Fc
r
r = a; meniscus
r = b; bottom
40 45 50
0
1
2
Igor-Bricker sample
T=20.0oC24,000 RPM v
2=0.73 mL/g
Abs
orba
nce
r2/cm
2
)2
))(~1(exp()()(
222
2
RT
arvMacrc
SvedbergNobel PrizeChemistry, 1926
OK, so let’s look at 5 applications
1. Can we measure the viscosity in a nanoreactor? (DLS)
2. Can we watch a bio/nano particle change? (DLS & LS)
3. Nanotech needs scaffolds: will they stand still? (FPR)
4. Controlling self assembly. (DLS)5. 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 DLSPTFE latex microrheology of
polyacrylamide gel
1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10
1.0
1.2
1.4
1.6
1.8
2.0
2470 s
1630 s
1340 s
1130 s
470 sg(
2)()
/sCamins & Russo, Langmuir, 4053, 1994See also: Piazza, Tong, Weitz
1
PTFE Particles
~ 250 nm
More ZADS
0 1000 2000 30000.0
0.2
0.4
0.6
0.8
1.0
Time/s
Fra
ctio
n F
roze
n b
y G
ela
tion
1
Seedlings
Sick Plants And close-up of mosaic pattern.
http://www.uct.ac.za/depts/mmi/stannard/linda.html
1
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 ~ -1 & Dtranslation ~ -1
Bottom line: TMV or nanoparticles can report the viscosity more or less accurately in a
small system.
100 1000 10000 100000 1000000 1E71
10
100
T
R
/
cP
Dextran MW
0.76 ± 0.01
(C)
1
“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
0 2 4 6 8
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
5.2
5.4
= 45o
= 90o
From910921 ph 7.4 900 ± 30 Å From924935 ph 5 xxx min 1330 ± 30 Å From938949 ph 5 xxx min 1710 ± 50 Å
ln(I
/arb
itrar
y)
q2/1010cm2
Guinier plots. ILS vs. q2
pH 7.4 900 ÅpH 5 1330 ÅpH 5 later 1710 Å
2
Dynamics of Flu “opening up”: Addition of citric acid for pH change is shown by the line
at time 0.
-400 -200 0 200 400 600 800 1000 1200 14000
200
400
600
800
1000
1200
Rh
Rh /
Å
t /s
0
20
40
60
80
100
120
140
160
180
200
Intensity
Intensity/kcps
2
Sproing!!!
pH
2
Forms a reversible gel scaffold.
O
O
PSLG: poly(stearyl-L-glutamate)
3
Temperature-ramped modulation FPR
0 1000 2000 30000
1
2
3
4
Schmidtke et al.
Figure 6
scan1062
Melt at 30.9oC
2040 s
start ramp @ 0.3oC/min
Con
tras
t (A
C/D
C)
t (seconds)20 30 40 500
100
200
300
400
500
600
700
Schmidtke et al.Figure 7
combinehigh
DDSC
TRFPR: 30.7oC
DSC
DS
C (W
) or
DD
SC
+60
0 ( W
/ o C
)
T/ oC
20 30 40 50
1
2
AC
/DC
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
hydrophilichydrophilic
hydrophobic
4
OH
OH
OH
NH
OH
OH
OHNH
OO
O
OH
OH
OH
NH OH
OH
OH
NH
OH
OH
OHNH
OO
O
OH
OH
OH
NH
Arborol example: [9]-10-[9]
9 watery hydroxyl groups
10 oily methylene groups
4
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 systemReversibleEasy to vary headgroup and core sizePossible 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!
• How would we know? Analysis!• What if we did? New Physics &
Materials!
Terminator
4
Self-assembly of [9]-12-[9] by DLS
Self-assembly of Dilute Arborols—Rh
0 1 2 3 4400
500
600
700
800
900
1000
1100
1200
1300
Rh/
(Å)
Number of Days
[9]-10-[9]only [9]-10-[9] plus [9]-6
Rh got from linear fit of gamma vs q2 of DLS data at five angles: 40, 50, 60, 70 and 90.
4
New problem: Hexaruthenium terpyridyl supramolecular structures
2 is the key monomer for
the supramolecule.
5 aids in Proof of structure.
Newkome et al.Angew.Chem.Int.Ed.1999, 38(24) 3717-21
5
Molecular snowflake by two methods
5
Data on supposed snowflake supports several scenarios, but self assembly
surely occurs
Same Data, Different Analysis0.5% (NMR conc.)
80% @ M=1340 M=325020% @ M=5600 + non-sedimenting stuff
0.006% (low!) M = 2600
5
Write the terpyridyl aggregate in shorthand form.
5
We see evidence of aggregation by SAXS, confirmed by DLS.
nStacked disks?
ContinueIn this wayto make aggregates of aggregates of aggregates etc.
Note that this alphabetretains symmetry similar tothe atomic alphabet
?
5
ConclusionsThe 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!
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